color atlas of small animal necropsy 1

. Inasor

, -- - ~ - - - -

First Edition

by

Color Atlas of Small Animal Necropsy

Richard E. Moreland, BS, DVM Necropsy Coordinator

Antech Diagnostics

Irvine, CA

REMSOFT PUBLISHING www.remsoftpublishing.com

2009 1

Statement of Copyright

Copyright 2009 by Remsoft Publishing. All rights reserved.

No part of this publication may be reproduced, stored in a retrieval system, or transmitted in any form or by any means electronic, mechanical, photocopying, recording or otherwise without the prior permission of the publisher.

ISBN: 978-0-557-07597-3

102509V15

2

Table of Contents

CHAPTER 1: BASIC PATHOLOGY DEFINITIONS Importance of Necropsy.. .... ......... ...... ................................... ............ .................. 7 Basic Pathology Definitions.. ........... . .. ................ ...... ..... .................. .................... 7 Basic Pathological Changes........... ....... ............................................................... 8

CHAPTER 2: Pre-Necropsy and General Considerations When and Where To Do A Necropsy ........................................ ... .......................... 10 Basic Equipment ................................................................................................ 11 Protective Clothing ..................................... . ......... ............................. .. ............... 12 The Submission Form ...................................................................... . .. . ... ............ 13 Ancillary Specimen Submissions ..... ... .............. ..... ................................. ......... .... 14 Common Postmortem Changes ............................................................................ 15 Describing Gross Lesions ......................................... .. ......................................... 17 History ............ .................... . .... ......... ............ ................................... ..... ............. 18 Routine vs. Cosmetic Necropsy ..................... ....... ... ............................. ................ 19

CHAPTER 3: THE NECROPV PROCEDURE Overview ................... .. ................ . ............................................ ........ ....... .......... 21

External Exam .... .. ............................................................................................. 21 Limb and Skin Reflection .......................................................... . ......................... 23

Icterus .. ..... .......... .. .......... .. ............. . ... ..... ...... .. ................ ..... .... .................... 24 Removal of the Tongue and Trachea .................................................. ................ .. 25 Opening and Examining the Abdominal Cavity .................................................... 27

Feline Infectious Peritonitis ... '" ...... .......... ... ........ ..... .............. ..... ...... ....... ....... 29 Malpositions ........... .. ............................. .. ... .......... ...... ...... ........... ...... ......... .. 31

Opening and Examining the Thoracic Cavity .......................... ............................. 32 Removing the Heart and Lungs ........... ....... ............. ............................................ 34

Pneumonia ......................... ..... ....... ....... ................................. ........ .......... .... 37 Opening and Examining the Heart .......... .. .......................................................... 38

Thrombosis and Postmortem Clotting ...... ......................... ..... ............ ...... ... ...... 42 Removal and Examination of the Liver ............................ .... ... .. ............. ... .......... .. 44

Necrosis ................................... .. ................................................. ... ............... 46 Opening and Examining the Intestine .................................................................. 50 Examination of the Pancreas ........... .................................................................... 54 Removal and Examination of the Spleen .............................................................. 55

Hemangiosarcoma .......................................... ............................................... 57 Removal and Examination of the Adrenals ........................................................... 59 Removal and Examination of the Kidneys .................................................. .... ..... . 60

Amyloidosis ........................... ..... ........... ....... ................................................ 62 Removal and Examination of the Bladder ............................................................ 65 Removal and Examination of the Brain ................................................................ 66

CHAPTER 4: THE NECROPSY REPORT Writing the Necropsy Report ........................ .......................... .......... ................... 70 Writing the Necropsy Conclusion ....................... .... ... ............................... ........... 70

CHAPTER 5: COMPLETE NECROPSY REPORT EXAMPLE .......................................... 71

Preface

Necropsy is the purest form of pathology. It involves the direct visualization of diseased organs and (

tissues and can provide invaluable infortQation, not only about the animal being necropsied, but about the cause, progression, and possible outcome of diseases in other patients. Necropsy results can provide feedback on implemented therapies and confirm or deny clinical assumptions and diagnoses.

Most people consider necropsy as just the gross dissection of a carcass. A complete necropsy, however can be considered to be a 4 stage process.

The first stage is the pre-dissection preparation. Proper preparation includes consideration of where and when the necropsy will be done, as well as the gathering of all necessary equipment and supplies. Proper preparation significantly increases the efficiency of the dissection and the prosector's ability to recognize and interpret lesions. Part of the pre-dissection stage is the gathering and consideration of the history. History is of paramount importance, impacting-not only the course of the dissection itself, but the final conclusions as well .

The second stage is the gross necropsy dissection itself. As with all diagnostic procedures, the usefulness of a necropsy for drawing proper conclusions is only as good as the data (in the case of necropsy, lesions) from which those conclusions are drawn. The primary goal of the dissection stage of a necropsy is to dissect the carcass in a systematic manner to assure that all important organs and tissues are visualized with maximal exposure to avoid overlooking important lesions. Specimen collection for ancillary tests are also carried out during the dissection stage. .

The third stage is the handling of collected specimens taken during dissection for ancillary testing. These specimens are submitted to the proper laboratories for processing, and the results compiled on completion. The premier ancillary test associated with necropsy is histopathology, however other tests such as microbiology, virology, and toxicoJogy may be very important, even pivotal, in reaching proper conclusions.

The fourth stage is the writing of the necropsy report and the conclusions. The necropsy report is the compilation of all of the data collected from the other three stages. The conclusion is the comprehensive interpretation of all of the data, including the history, the gross lesions, and the results of ancillary tests. The stronger the data from all stages, the more accurate the conclusions.

The main goal of this book is to outline the proper standardized necropsy dissection procedure for small companion animals . It is an attempt to increase the usefulness of necropsies in the clinical setting by 1) insuring all gross lesions are visualized for interpretation, 2) familiarizing the prosector with examples of common gross lesions, and 3) refreshing the understanding of basic pathology concepts and pathogeneses important in the proper interpretation of necropsy findings.

4

Acknowledgements

First and foremost I would like to thank my family (Cynthia, Miles, Amber, and Kristen) for their patience and understanding throughout this long and time consuming process. Special thanks to my daughter Kristen for her help with some of the book's graphics and cover art. I am very grateful to Dr. Earmie Edwards of Lancaster Pet Clinic in Lancaster, CA for her invaluable help in

editing the manuscript. Lastly, I extend my appreciation to the professionals and staff at Antech Diagnostic in Irvine, CA for their assistance, both direct and

indirect, on this project.

5

' )

6

Chapter 1 Basic Pathology Definitions

THE IMPORTANCE OF NECROPSY

Necropsy is the animal analogy to human autopsy. At its core, it is the systematic dissection and examination of an animal carcass to search for abnormal anatomical changes (lesions) in the tissues. It is generally used to determine the cause of death, but is also used to chronicle disease progression. Necropsy is the purest form of pathology. It involves the direct visualization of diseased organs and tissues (grossly and/ or microscopically) and can provide a wealth of information, not only about the animal being necropsied, but about the cause, progression, and possible outcome of diseases in other patients. Necropsy results can provide feedback on implemented therapies, and confirm or deny clinical assumptions and diagnoses.

?bviously, a knowledge of the normal anatomy IS necessary to make a distinction between normal tissues and lesions. The proper, standardized necropsy procedures are designed to allow the prosector (the person doing the necropsy) maximal exposure of organs for maximum visualization of possible lesions.

Obtaining the maximum benefit and information from a necropsy requires not only knowledge of the proper necropsy dissection procedure, but knowledge of basic disease processes. In particular an understandil).g of basic pathology processes is paramount, starting with standard basic pathological definitions.

BASIC PATHOLOGY DEFINITIONS Pathology is the study of disease .

Disease is any variation from the normal morphology or physiology of a living organism. Disease results from various causes, such as infection, genetic defect, or environmental stress, and is characterized by an identifiable group of lesions, clinical signs, and/ or symptoms. Diagnosis of disease is important for proper treatment.

Anatomical pathology strives to diagnose disease by concentrating on those anatomical (morphological) changes in living tissue at the gross and microscopic levels.

Clinical pathology strives to diagnose disease by the use of tests on various body fluids and body waste products. These include blood plasma, urine, cerebrospinal fluid, sputum', saliva, peritoneal fluid, thoracic fluid, and feces.

Lesions are recognizable morphologic (anatomic) changes in tissues, either grossly or microscopically.

Clinical signs are changes in behavior or function that are observable by a third party which indicates disease. Limping is an example of a clinical sign which would suggest a broken leg (a lesion). The terms "clinical signs" and "symptoms" are often used interchangeably, although technically symptoms are changes in behavior or_function which cannot be observed objectively by a third party. Symptoms can only be detected by the individual (such as the pain of a headache), however it may cause the animal to behave in a way that is detectible as a clinical sign (such as head pressing).

Morphologic diagnosis is a short phrase in which the most important aspects of tissue changes (either gross or microscopic) are summed up and communicated.

The most important part of the morphologic diagnosis is the naming of the lesion, with other components giving specific information about the lesion .

The elements of the morphologic diagnosis are:

Severity

Duration

Distribution

Anatomic site

Miscellaneous adjectives/modifiers

Lesion

Examples of a complete morphologic diagnosis:

Severe, acute, multifocal, renal tubular coagulation necrosis"

Marked, chronic, focally extensive, lymphoplasmacytic, cholangiohepatitis"

7

Chapter 1 Basic Pathology Definitions

An etiology is the cause of a disease or lesion. Etiologies are numerous and diverse and include infectious agents such as bacteria, fungi, or parasites, and physical damage such as blunt force trauma or thermal burns (to name a very few). An etiologic diagnosis names the etiology (ex. Histoplasmosis) . Determining the etiology when possible is very important as it often dictates proper treatment.

Disease Names: When a condition features a unique combination of lesions, clinical signs, and/ or symptoms, that condition may be given a name. For example, a disease of young puppies caused by a morbillivirus that results in pneumonia, encephalitis, and the formation of eosinophilic inclusion bodies in epithelial tissues has been named Canine Distemper.

BASIC PATHOLOGICAL TISSUE CHANGES (LESIC}NS) Broadly speaking, the primary lesions detectib1e grossly and/ or microscopically in body tissues include degeneration, necrosis, inflammation, and neoplasia.

Degeneration represents the gradual deterioration of cells or tissue due to the loss of specific cellular functions and manifested in specific morphologic abnormalities. Degeneration is usually reversible if the cause is reversed. Examples include cloudy swelling and hydropic change of hepatocytes, resulting from the failure of plasma membranes sodium-potassium pump to keep out water.

Necrosis is the morphologically recognizable death of cells and/ or tissue. Necrosis is not reversible. In general, changes in the nucleus of cells are the primary indicators of necrosis. These changes include pyknosis, karyorrhexis, and karyolysis. A pyknotic nucleus is one which has shrunken and become very dense and dark, with little if any recognizable chromatin. A karyorrhectic nucleus is one which has fragmented into several pieces. A karyolytic nucleus features a slow loss of nuclear chromatin, resulting in a very faded appearance.

Inflammation is the vascular and cellular response of the body to injury. Grossly, inflammation is characterized by a swelling and reddening of the affected tissue. Microscopically, inflamed tissues feature the presence of vascular congestion, edema, and the presence of one or more types of inflammatory cells. The types of inflammatory cells present usually give some indication of the cause of the inflammation.

Neoplasia (tumor, cancer) is the abnormal and uncontrolled proliferation of body cells. All tumors originate from some existing tissue/body cell. Neoplastic cells usually try to mimic their tissue of origin, which is an important feature in helping to identify them. Broadly, all body cells can be classified as either epithelial or non-epithelial.

In naming tumors, those that arise from epithelial cells and are determined to be benign are designated with the suffIx -oma appended to their tissue / cell type (hepatoma, mammary adenoma). Those that arise from epithelial tissue and determined to be malignant are designated with the suffIx -carcinoma (hepatocellular carcinoma, mammary adenocarcinoma). Tumors of non-epithelial origin and determined to be benign also use the suffIx -oma (fibroma, osteoma). Tumors of non-epithelial origin and determined to be malignant use the suffix -sarcoma (fibrosarcoma, osteosarcoma). There are numerous exceptions to these rules, with lymphoma and melanoma being two glaring examples.

8

Chapter 2 Pre-Necropsy and General Considerations

WHEN AND WHERE TO DO A NECROPSY

The best time to do a necropsy is immediately after the death of an animal to minimize postmortem autolysis. When a necropsy has to be delayed, the carcass should be refrigerated. Refrigeration slows, but does not stop, autolysis by slowing down enzymatic reactions. If

possible, avoid freezing the carcass. For one thing, it is impossible to necropsy a frozen carcass and thawing can take 24 hours or more depending on the size of the carcass. More importantly, however, ice crystals which form during freezing damages the tissues at the microscopic level making histopathology more

difficult~. However, if the necropsy is to be delayed for a week or more, freezing is preferable to the prolonged but continuing slow autolysis of refrigeration,.

The necropsy location should have adequate

light, water, ventilation, drainage, and

provisions for cadaver storage and disposal. In

clinical settings, necropsies are often done on

an exam table, however these tables do not

provide for drainage of blood and fluids (except

over the side on to your shoes). Ideally, a

bathtub with a slatted grate or a wet prep table

should be used to allow drainage. Larger,

dedicated necropsy rooms may have a

customized stainless steel necropsy table.

Some feature downdraft ventilation in the table

to minimize odor. Wherever the necropsy is

done, the pro sectors should have easy access to

their basic necropsy equipment, a lined

biohazard garbage can for excised tissue,

formalin containers, and toxicology and

microbiology collection materials.

Pre- and post storage of the cadaver and

necropsy remains requires some form of

refrigeration. This can be problematic for large

animals. In larger dedicated necropsy rooms,

large walk-in coolers are often used. In smaller

necropsy rooms, an open top refrigerator may

suffice .

Figure 1: Wet prep table.

Figure 2 : Dedicated necropsy room and necropsy table.

Figure 3: Specialized necropsy table with downdraft ventilation and built-in disposal.

10


BASIC NECROPSY EQUIPMENT

The choice of equipment for necropsy depends in part on the size and type animal, the type of examination requested, and the individual preferences of the examiner. Most small animal necropsies will require:

One or more sharp boning knives

Scalpel

One or more pairs of specialized scissors

One or more pairs of specialized forceps

A ruler (plastic or metal) and a tape measure

An ink pen/marking pen and note paper

A plastic cutting board

Large syringes for collecting and measuring fluids

Some means of cutting bone; either manual hacksaw, bone shears, and/or a Stryker saw.

Plastic or metal containers for temporary viscera holding

G A scale of some type for weighing organs

Formalin-filled container for collection of tissues for histopath

Multiple, variably-sized Whirl-Pak or Ziploc bags for fresh tissue collection

Digital camera (optional)

Supplies and containers for collecting specimens (formalin jars and whirl-pak bags)

Figure 1: Basic necropsy equipment

Figure 2: The Stryker saw is a special motorized saw used for cutting bone. Essentially the same as a cast cutter, it is used primarily for cutting the flat bones of the skull to remove the brain. The blade oscillates, so it only cuts bone and not soft tissue.

Figure 3: 10% neutral buffered formalin

Figure 4: Whirl-pak bag

Figure 5: Digital camera

11


:PROTECTIVE CL9THI~G

The wearing of protective clothing is meant to protect the examiner from contamination with blood, tissues and body fluids from the cadaver that are potential carriers of infectious particles. The best protective clothing should provide comfort to the examiner while not compromising protection against possible contamination. The primary clothing should be either surgical scrubs or cotton utility coveralls.

Ideally, a second outer covering such as a surgical gown or a plastic apron should be worn to give added protection. Unless they are disposable, these articles must be washed clean and disinfected after each use.

Disposable paper booties are good for providing protection for your footwear from contamination, however, many formal necropsy rooms are often wet environments. If the necropsy is done in such a wet environment, rubber boots should be worn.

Proper gloves are paramount when performing a necropsy. Although latex surgery or examination gloves are often used, they generally are not hardy enough for a full necropsy on animals larger than small rodents, young kittens, or puppies. A pair of ordinary garden or kitchen latex gloves of appropriate size are best for performing a necropsy on most dogs, cats, and large animals. Compared with the latex glove, the latter are less expensive, more durable and provide greater protection. The gloves should fit the hands and fingers of the examiner without interfering with manual dexterity and causing numbness.

Facemasks, face shields, or goggles are generally not used doing a routine necropsy unless a contagious zoonotic disease is suspected and additional protection is deemed necessary. Disposable paper facemasks cleared by the FDA for use as medical devices have been determined to have specific levels of protection from penetration of blood and body fluids, keeping unlikely splashes or sprays from reaching the mouth and nose. They are not designed to protect against breathing in very small particle aerosols that may contain viruses.

Contrary to popular belief, face masks do not mute odors. Odors from a recently deceased or quickly refrigerated carcass should be minimal. Obviously the more autolytic the carcass, the worst the odor will be. Most prosectors generally get use to even strong odors within the first few minutes of the necropsy. In particularly autolytic and rank carcasses, practical techniques such as placing Vicks VapoRub ointment underneath the nostrils to mask the odor can be employed.

Figure 1: Scrubs Figure 2: Plastic apron

Figure 3: Paper booties Figure 4: Rubber boots

Figure 5: Gloves

, 1

Figure 6: Disposable paper facemask 12


THE SUBMISSION FORM The style and type of necropsy submission forms vary from laboratory to laboratory, depending on the mode of document storage and retrieval system in use,

At a minimum, submission forms should include the following information:

Clinic Identification - Clinic name, ID#, address, phone number, doctor's name

Case Identification - Assigned necropsy case number, clinical case number, and the date of submission and examination

Owner's Identification - Owner's name, address (optional), and phone number (optional)

Specimen Identification - Animal's name, species, breed, age, weight, and sex

Clinical History! - Includes the details of clinical findings, signs and symptoms observed (especially perimortem signs), and the clinical diagnosis, Use the back or additional sheets of paper if necessary,

..".",:;a..:rzc::~ @ 0 I G " 0 ~ T , (: , RlJROEll RlRM . ' r LAB USE Q.~Y

OATE -Icutln I I I ~E

OOCTOR I I CHARTt I I ~ 0 CAN'NE 0 F.Ql)JlJE 8 REED ~o;l A.G&, ~ 0 FEliNe 0 "\~AN I O M ~ OlhCf OF OSF

,

CHOOSE Ii you wool

- -----_.-----------------------------------------

Chapter 2 pre-~opsy and General Considerations ANCILLAl{Y SPECIMEN SUBMISSIONS Obtaining a definitive diagnosis from gross lesions alone is often not possible and may require the use of other ancillary laboratory diagnostic procedures. Specimens for those diagnostic procedures may be collected during the necropsy as deemed necessary. Specimens are often collected for:

e Histopathology: Specimens should be routinely collected from every major organs in all necropsies

Microbiology: Specimens are only collected when the history, clinical diagnosis, or necropsy lesions suggest a causative infectious agent

Toxicology: Specimens are only collected when the history, clinical diagnosis, or necropsy lesions suggest a toxic agent (poison).

Histopathology Histopathology is the primary ancillary test associated with necropsy and is often the test which provides the definitive answers in many cases. Collection of histopathology samples should be a part of all gross necropsies.

What Specimens To Collect: Ideally, samples for histopathology should be collected from all of the major organs. These include the heart, lung, liver, spleen, kidneys, bladder, pancreas, stomach, small intestine, large intestine, thyroids, mesenteric lymph nodes, adrenals, and brain. When obvious lesions are present in these tissues they should of course be sampled, however, when no lesions are present, 1 or 2 random samples should be taken from each tissue. When it is not feasible to take samples of all major organs, and there are no obvious lesions, priority should be given to those organs and tissues which correlate most with the primary clinical signs observed (i.e. GI for vomiting, lung for dyspnea, etc.). All specimens should be immediately fixed in 10% neutral buffered formalin. Formalin stops all autolysis and hardens the tissue in preparation for being cut thinly for microscopic slides. The specimens should be collected as soon as possible and should not be more than 1.5 cm thick. Collected tissue should be placed in a volume of formalin that is 10 times the tissue volume to ensure proper fixation .

Microbiology Specimens intended for microbiological examination should be collected aseptically as possible. One technique is to sear the surface of the organ or tissue With a hot spatula, then

incise and collect the required material from the deeper portion of solid organs" abscess, or coagulated masses. From this incision, sterile swabs, tissue fragments, and aspirates may then be taken. Place sterile swabs and aspirates in a special transport media, especially if the suspect organism is a fastidious one. The choice of transport media depends largely on the microorganism suspected to be present in the specimen. If cultures are required, sterile swabs should be used immediately before fully exposing body cavities or openings. Hollow organs such as segments of the gastrointestinal tract are best handled by obtaining a loop of intestine tied at both ends and placing them in a sterile petri dish.

Toxicology Materials for toxicological examination should be collected without contamination by chemicals being used during necropsy. Chemicals that may contaminate the specimen include fixatives, detergents and disinfectants routinely used during necropsy. Although different toxicants require specific samples for chemical analyses, in general certain tissue samples are best. These include whole blood and sera, tissue blocks (about 100 grams) of both liver and kidneys, urine, and stomach and intestinal contents. -

Contact the toxicology laboratory where the samples will be sent to ensure that the right specimens and amount ar~ collected and that adequate precautions for handling and preservation are observed.

It is important to note that most laboratories do not have the capabilities to do "toxicology screening", i.e. checking a single sample for a wide range of possible toxins (like they do on CSI). In general, specific tests can be run for specific toxins, each test having it's own associated cost. Obviously, random testing is impractical, so it is important to have some idea of what toxin to test for. The problem is that most toxins cause death without producing significant (or any) gross or microscopic lesions which might give clues to the cause. Generally, the most important information on which toxin to check for comes from the clinical history and/ or antemortem clinical signs. While toxicology screening is not widely available, toxicology panels, in which a group of individual tests are run together, are common. A common toxicology panel would include those compounds commonly used in malicious and/ or accidental animal poisoning such as strychnine, arsenic, metaldehyde, and warfarin.

14


COMMON POSTMORTEM CHANGES

When an abnormality is found during necropsy, it must be judged whether it is an

' antemortem lesion or a postmortem change. Antemortem lesions occurred before death and therefore may have contributed to the death or disease of the animal; postmortem changes occur only after death and therefore cannot have contributed to the death of the animal. Judging which is which is very important so that a proper interpretation can be made.

Postmortem autolysis result from the ,,\r~ degradation of tissues associated with the release of proteolytic lysosomal enzymes from tissue cells when they die, as well as from the action of postmortem bacterial enzymes (putrefaction). Bacteria that form part of the normal microbial flora in the intestine proliferate soon after death. Invasion of organs and tissue occurs primarily through the vessels and lymphatics.

Postmortem autolysis can be slowed by decreasing the animal's temperature via refrigeration soon after death. Since most lysosomal enzymes and bacterial enzymes are temperature dependent, lower temperatures slow (but does 'not completely stop) the degradation of the tissues. Lower temperature also inhibits bacterial growth. Freezing is not, however, recommended because the ice crystals which form damage cells and can make this histopath difficult to interpret.' Still, if the necropsy must be delayed a week or more, freezing is recommended since the continued degradation of tissue refrigerated longer than would have even more harmful consequences.

Figure 1: Hemoglobin imbibition of the small intestine

There are several tissue changes which can occur after death however the more common postmortem changes seen at necropsy include hemoglobin imbibition, pseudomelanosis, and livor mortis.

Hemoglobin imbibition is the pinkish to reddish coloration imparted to tissues due to the lysis of red blood cells. It is most evident on the outer surfaces of light-colored organs like the intestine or brain, or on the inner surfaces of large arteries or in the heart.

Bile imbibition is the greenish-yellow coloration imparted to tissues in contact with the gallbladder after death. This is usually seen on the surrounding liver tissue, as well as on loops of gut.

Pseudomelanosis is a blue-green to blackish discoloration imparted to tissues due to the action of bacteria on hemoglobin, resulting in the formation hydrogen sulfide and iron sulfide. This discoloration is often black within the anaerobic environment of the abdominal cavity, but is often more greenish in the more aerobic environment of the skin.

Livor mortis (hypostatic congestion) is caused by the settling of blood to the down side of the animal's body due to gravity. This gravitational settling of blood and body fluids results in a darker reddish coloration of the orgahS and tissues on the down side of the cadaver.

Figure 2: Hemoglobin imbibition of the brain 15


Figure 3: Pseudomelanosis of the kidneys . In the anaerobic abdomen, pseudomelanosis has a black to dark blue-green hue

Figure 5: Pseudomelanosis in the ventral abdominal skin. In the more aerobic environment of the skin, pseudomelanosis has a lighter green hue.

Figure 7: Pale pox-marking of the liver and small gas bubbles due to bacterial putrefacation.

Figure 4: Pseudomelanosis of the pancreas

Figure 6: Livor mortis in the lungs. Blood has settled in the left lung lobes due to gravity, making them much darker than the right lobes

Figure 8: Though this looks like a myocardial infarct, it is only an area of postmortem autolysis 16


DESCRIBING GROSS LESIONS

The general rule in recording necropsy findings is to be descriptive rather than interpretive. Interpretation of lesions should be described in the diagqosis and/ or conclusion section.

When applicable tissues/lesions should be described by:

Shape/margins (irregular, circular, ovoid, oblong, polypoid, botryoid, wedge-shaped, papillary, pedunculated, indistinct, well-demarcated, infiltrative, etc.)

.:IConsistency (hard, firm, gritty, soft, rubbery, spongy, viscous, friable, etc.) ~ Color (black, brown, mahogany, grey-green, red, tan, white, off-white, yellow) lJSize (measured in centimeters) ::JDistribution and location (bilateral, unilateral, diffuse, focal, multiple, multifocal, patchy, etc.) u Surface appearance (bulging, ulcerated, eroded, rough, reticulated, smooth, pitted, umbilicated,

verrucous, etc.)

Figure 1: "Lung and liver lobes are characterized by multifocal, coalescing dark circular lesions in the parenchyma. These lesions vary in size from .2 to . Scm, and have a firm consistency on palpation." (Metastatic melanosarcoma)

Figure 3: "Both kidneys feature similar pathological changes. Both kidneys are enlarged with slightly distorted conformation. There are multifocal, variably sized, pale, firm masses present throughout the renal parenchyma. Many blood vessels contain large occlusive thrombi and scattered areas of the parenchyma are reddened. Gross Diagnosis: Bilaterql, multifocal irregular renal masses with vp.scular thrombosis and hemorrhage (Fungal infection - Phycomycosis).

FigUre 2: "The kidney features multifocal, roughly triangular, pale areas in the cortex. Each is bordered by a thin zone of reddening and are approximately 1 x 2 em in size. " (renal cortical infarcts)

17


HISTORY The importance of a good history cannot be overemphasized. Arriving at a proper diagnosis and/or cause of death often depends strongly on the information gathered from the clinical history. The history gives the prosector clues about which organ systems might be more important in the disease process, warranting greater scrutiny. The history may suggest the examination of tissues not normally evaluated during the course of a routine necropsy (spinal cord, inner ear, sinus cavities, etc.). The history may suggest the collection of certain tissues for ancillary tests (toxicology, microbiology, etc.) which are not normally collected during a routine necropsy. While the history does not affect what is seen at necropsy, it will affect the interpretation of what is seen. Consider the following examples.

Figure 1: Edema fluid in tissues appears as a clear translucent, almost gelatinous material. It can be seen here in the subcutaneous tissues of a dog's forearm. This is a good example of subcutaneous edema.

Figure 2: A similar clear translucent fluid layer is present here in the skin taken from the dorsal back of a dog. Subcutaneous edema would be the most likely interpretation. Subcutaneous edema suggests many possible pathogenic scenarios including heart failure and/ or hypoproteinemia. However, the history indicated the animal was being given therapeutic subcutaneous fluids in this area. This fluid is, in fact, the result of that therapy and not from pathological edema. Without that history, many erroneous interpretations of this lesion could have been made.

)

18


ROUTINE VS. COSMETIC NECROPSY A routine necropsy is the standardized, systemic gross dissection of the carcass whose goal is to assure that all important organs and tissues are visualized with maximal exposure to avoid overlooking important lesions . Since the aim of the technique is thoroughness, there is considerable mutilation of the carcass.

A cosmetic necropsy is one where the dissection is not as extensive (or as mutilating) as in a routine necropsy. It is commonly requested by owners who have a strong aversion to the mutilation of their pet, and/or wish some post-necropsy viewing of the body. Such necropsies are not nearly complete and may result in missed lesions, and, as such, are not recommended.

The cosmetic necropsy involves the bulk removal of the internal organs through a single ventral midline incision. Visualization of organs and lesions can be difficult, and many of the cuts needed to remove the organ have to be made blindly.

Cosmetic Necropsy Procedure w Make a single incision through the skin, muscles, and peritoneum in the ventral abdomen,

extending from the xiphoid process approximately the mid abdomen

.J Visualize the abdominal cavity through the incision and make note of any fluid accumulations. Assess the orientation of the organs for possible malpositions .

.J Incise the diaphragm, making note of the presence or absence of negative pressure in the thorax. Cut the diaphragm as completely as possible from its attachments .

..J Reaching as far as possible into the cranial mediastinum, cut the esophagus, trachea, and cranial mediastinal vessels at the thoracic inlet

..J Remove the heart and lungs by pulling the esophageal-tracheal stump through the abdominal incision, tearing or cutting them free from their dorsal attachments

.J Cutting the root of the mesentery will allow the liver, stomach, spleen, and small intestines to be partially extracted through the skin incision. Cutting the colon as far caudally as possible will allow full removal of the viscera .

.J Identify the kidneys and remove them. If visible, identify and remove the adrenal glands .

...l Identify and remove the bladder .

.J Drain any fluids remaining in the cavities. It is a good idea to place old newspapers in the abdominal cavity so that it does not have a sunken appearance when closed .

...l Suture the abdominal incision to close the abdomen .

...l The brain is removed only if the history suggests a neurological problem.

o Make a midline incision between the eyes towards the level of the first cervical vertebra. Dissect the skin and reflect all muscles covering the calvarium, cutting them towards the sides.

u Using whichever bone cutting implement you have available, cut the calvarium to expose the brain.

o Sever the spinal cord and lift the brain carefully. Cut all of the nerves at the base of the brain. Tilt the head upward and backward to simplify removal of the brain from the cranial cavity.

Q Replace the calvarium, reposition the muscles and skin, and suture the skin closed.

Examine the removed organs per the usual routine as normal and take whichever specimens deemed necessary

~e carcass should De returned to as near a pristine state as possible . Clean any blood and fluids ::-om the hair coat. Sutures should be continuous and as neat as possible.

19

Chapter 3 The Necropsy Procedure

OVERVIEW The goal of the gross dissection phase of the necropsy is the removal and close examination of the major organs for lesions, and for the collection of tissue samples for further ancillary testing. In most animals this involves the reflection of the front and hind limbs on one side to get greater access to the thoracic and abdominal cavities. Once the body cavities are exposed, cursory examination of the organs is performed prior to the complete removal of the organs, with the more detailed organ examinations performed outside of the body.

In a routine necropsy, there is not generally a detailed dissection of the musculoskeletal system, joints, spine or spinal cord, the eyes, s inus cavities, or the inner ears unless the history, clinical signs, or obvious necropsy changes warrant detailed attention.

Figure 1: Traditionally, animals are positioned . ~ left lateral recumbency. This animal is severely emaciated (cruelty starvation case).

Figure 3: Sublingual oral fibrosarcoma

STEP 1: EXTERNAL EXAM Position the carcass on the table in left lateral recumbency. Carefully examine the animal's exterior. Measure the carcass length from tail base to nose-tip . Observe the eyes, ears, and other body openings for the presence of secretions or excretions, prolapse, and abnormal coloring of mucus membranes. Examine the hair coat, and note for the presence of ectoparasites, areas of alopecia, thickening of the skin, tumor masses, and possible wounds. Palpate the continuity of bony structures and look for evidences of fractures, enlarged joints, and abnormal masses. Open the mouth and examine the oral cavity (if rigor permits). Many types of abnormalities are evident from the external exam.

Figure 2: Alopecia and hyperpigmentation (demodecosis)

Figure 4: Blood in the anterior chamber of the eye (hyphema) 21


Figure 5: Glossal and gingival fungal lesions (Cryptococcosis)

Figure 7: Corneal ulceration and inflammation (ulcerative keratitis)

Figure 9: A large sublingual cystic mass full of collected saliva resulting from a ruptured salivary duct (a sublingual mucocele or ranula)

Figure 6: Glossal and gingival fungal lesions (Cryptococcosis)

Figure 8: Marked oral, ocular, and nasal planum icterus

Figure 10: Prior to the necropsy, x-rays of the carcass can be very useful in helping to localized broken bones and finding small metal projectiles

)

22


STEP 2: LIMB AND SKIN REFLECTION

Grasp and lift the right forelimb upward and cut all muscles between the subscapular area and the rib cage to free the limb. Reflect the leg dorsally. Hold the right hind limb up and cut down to the hip joint. Cut the joint capsule and the round ligament to free the head of the femur. Continue cutting through the soft tissue and reflect the freed hind limb to the dorsum of the specimen. Inspect the hip joint for signs of Degenerative Joint Disease or other changes.

Figure 1: Cut through the axillary region to reflect the front limb, and through the inguinal area to the coxofemoral joint to reflect the hindlimb

Figure 3: Both left limbs have been reflected along with the thoracic and flank skin to reveal severe subcutaneous hemorrhage. This i emorrhage resulted from the improper use of a . eating pad.

Connect the skin opening made when reflecting the front leg to the skin opening made when reflecting the hind leg by cutting beneath the skin along the right lateral thorax and abdomen.

Reflect the skin both dorsally and ventrally, exposing the subcutaneous tissues of the thorax and abdomen. The subcutaneous tissues should be inspected for hemorrhage, edema, icterus, and other lesions.

Figure 2: Connect the exposed areas from the two limb reflections and reflect the skin off of the trunk and thorax dorsally and ventrally.

Figure 4: Exposed coxofemoral joint. This joint features a thickened capsule and eroded femoral head cartilage with polishing of the underlying bone (ebernation). These are all signs of Degenerative Joint Disease .

23


ICTERUS A distinctive yellowing can occasionally be noted in the oral, ocular, subcutaneous, or abdominal tissues on necropsy. This yellowing is called icterus or jaundice and is caused by the deposition of the compound bilirubin. Bilirubin is a normal breakdown product of heme and icterus only occurs when it present in high amounts in the blood stream. Normal heme metabolism starts with the phagocytosis of old or damaged RBCs in the spleen by splenic macrophages. Hemoglobin is removed and separated into its heme, globin, and iron components. The iron is converted to ferritin and hemosiderin for storage and recycling. The globin is broken down into amino acids for recycling. The heme cannot be recycled and therefore must be excreted. It is first converted to unconjugated bilirubin wtthin the splenic macrophage, then transferred via the blood-stream to the liver while attached to albumin. Within the liver cell it is conjugated with glucoronic acid to become conjugated bilirubin. It is then put into the bile via the bile caniculi, the small tracts between the hepatic cords. Bilirubin is not a bile salt and does not aid in the breakdown of fat; it is only in the biliary system as a means of disposal.

The three primary mechanisms of icterus are intravascular or extravascular hemolysis, liver disease, and bile duct obstruction.

With hemolysis, the spleen is forced to deal with an excessive amount of heme, either from increased phagocytosis (extravascular hemolysis) or hemoglobin released into the bloodstream from lysed RBCs (intravascular hemolysis). With intravascular hemolysis some of the heme in the bloodstream (hemoglobinemia) will pass through the kidneys and into the urine (hemoglobinuria). Regardless of the type of hemolysis, the spleen produces excessive amounts of unconjugated bilirubin for processing by the liver. The liver is unable to process all of this extra bilirubin which

Figure 1: Oral, ocular, and nasal planum icterus

consequently remains in the blood-stream and Figure 2: Icterus of the subcutaneous and eventually stains the tissues yellow. In liver omental adipose tissue disease, the liver is unable to process even the normal amounts of bilirubin resulting from normal heme metabolism. The excess unconjugated bilirubin remains in the bloodstream and stains the tissues yellow. In addition, the swelling of hepatocytes causes some obstruction of the bile caniculi, resulting in a portion of the conjugated bilirubin gaining access to the blood-stream.

In biliary obstruction, the processed conjugated bilirubin from normal heme metabolism cannot gain access to the biliary system, spills over into the bloodstream and stains the tissues yellow .

Figure 1: Normal Heme Metabolism

... . Ihto

8U""

..

;

24


STEP 3: REMOVAL OF THE TONGUE, TRACHEA, AND ESOPHAGUS

Make a skin incision from the mandibular symphysis along the mid-ventral neck, to the thoracic inlet. Reflect the skin as before to expose the underlying structures.

The tongue must be removed to thoroughly examine the buccal cavity. Cut the muscular and tissue attachments of the tongue along the inner surfaces of both sides of the mandible. After cutting, the tongue can be pulled out through the floor of mandible . Reflect the tongue back to the pharyngeal hyoid bones, continuing to cut all muscular attachments. Cut through the hyoid bones by severing their cartilaginous articulations (the cornu).

Figure 1: Make a submandibular skin incision then reflect the skin

Once the tongue is reflected back, examine the palate, pharyngeal mucosa, and tonsillar tissues. Continue dragging the tongue backward and dissect free the trachea and esophagus, cutting all attachments back to the thoracic inlet. Identify and remove the thyroid glands and parathyroid glands.

Figure 2: Cut the muscles along each side of the mandible

Figure 4: Expose the oretropharyngeal hyoid bones

Figure 3: Pull the tongue out through the bottom of the mandible

Figure 4 : Cut the hyoid bones at their cartilaginous articulation (the "cornu")

25


Figure 5: Dissect the tissues covering the ventral neck to expose the ventral trachea

Figure 7: Identify and remove the thyroids and the parathyroid glands on the sides the trachea.

Figure 9: Marked tracheal hypoplasia (part of Brachycephalic Syndrome)

Figure 6: Reflect the tongue, trachea, and esophagus back to the thoracic inlet

Figure 8: Bilateral parathyroid hyperplasia due to renal failure (renal secondary hyperparathyroidism)

Figure 10: Tracheal collapse (part of . Brachycephalic Syndrome)

!

26


STEP 4: OPENING AND EXAMINING THE ABDOMINAL CA VITY

The abdominal cavity is opened by removing the abdominal (flank) wall along the ventral midline, the curve of the last rib, and dorsally at the level of the kidneys. Usually the abdominal viscera is initially obscured by fatty omentum which can be removed.

The viscera should be regarded in situ for obvious lesions, fluid accumulations, relative s izes, and malpositions, however, no detailed examination is done until all organs are completely removed. Inflammation of the peritoneal cavity (peritonitis) is generally :1oted by the presence of reddening and :-oughening of the serosal surfaces of the n sceral organs, along with the presence of ~brinous tags.

_illy abdominal fluids should be collected and ~antified. Broadly, abdominal fluids can be exudates, transudates, or btood. Blood in the abdominal cavity is referred to as a hemoabdomen. When large amounts of blood are present, it is important to try and :::etermine the source of the bleed before :-emoving the abdominal viscera as this ~enerally makes it more difficult to determine ::"1e origin. The presence of transudates and ::"'rudates in the abdominal cavity is calleq ascites. When transudates are -..mcontaminated with blood they generally :::'ave a clear yellowish (straw-colored) 2.flpearance. When blood is present it tints the :::'uid red and is referred to as serosanguinous. :are must be taken to avoid confusing actual ::-ank) blood with serosanguinous fluid. 3 ood's higher opacity and viscosity are ~enerally the best features to distinguish it =:-om serosanguineous fluid.

~e liver should be assessed in situ. Extension - ell beyond the last rib is considered ~epatomegaly.

-=-- e thoracic cavity should be assessed for ::egative pressure by inspection of the .:.:aphragm. Normally it should be pulled taut :.:ward the thoracic cavity. Puncturing it "-""ould produce an in-rush of air and a :=:axation of the musGle. If the muscle is =--eady relaxed prior to puncturing it, it is .=.dicative of pneumothorax..

Figure 1: Normal abdominal viscera

Figure 2: Enlarged liver (hepatomegaly), extending well beyond the last rib

Figure 3: Serosanguinous ascitic fluid. Though it looks like blood, its low viscosity as judged during the necropsy suggested it was in fact blood-tinged fluid. 27


Figure 4: Straw-colored ascitic fluid

Figure 6: Partially clotted straw-colored abdominal fluid with white nodular lesions on the serosal surfaces of the small intestine and mesentery (Feline Infectious Peritonitis - FIP).

Figure 8: The diaphragm is pulled taut against the thoracic cavity, confirming negative pressure within the thorax.

Figure 5: Marked abdominal hemorrhage (hemoabdomen)

Figure 7: An unknown intra-abdominal mass turned out to be a granuloma formed around gauze left from a previous surgery. This "gauze granuloma" is called a gossypiboma.

Figure 9: Here, the diaphragm is relaxed, indicative of air in the thorax (pneumothorax) and a lack of negative pressure. 28


FELINE INFECTIOUS PERITONITIS lFIP)

FIP is a serious, fatal, infectious but non-contagious viral infection of cats. It is caused by a mutation of the feline enteric coronavirus. FIP causes widespread pyogranulomatous inflammatory lesions throughout the abdominal visceral and/ or thoracic organs, and often a thick viscous yellow ascitic or pleural fluid . The widespread infection causes weight loss, anorexia, non-responsive fever, and eventually organ failure and death.

The disease pathogenesis involves complement fIxation and the release of vasoactive amines that causes increased vascular permeability and endothelial cell retraction. In addition, antigen-antibody complexes result in systemic vasculitis. These changes lead to the exudation of fluid and plasma proteins typical of the effusive "wet" form, as well as organ damage due to impaired blood flow. The wet form generally causes death within a few weeks. The "dry" form is more insidious, leading to death over a much longer period (often years) .

Testing for the disease clinically can be problematic. Exposure to the virus with the production of an antibody titer does not mean the virus has mutated and will cause FIP. Higher titers could be more suggestive, however some cats with fulminant FIP may have no titer. Most tests involve "statistical probabilities" that the infection is present. The albumin to globulin ratio (A/G ratio) is one such statistical method. If the ratio is less than 0.8, there is a 92% statistical chance the cat has FIP. If the ratio is greater than 0.8 there is a 61 % statistical chance the cat does not have FIP. Another statistical method is Rivalta's Test. This test is performed by taking a test tube that is fIlled with distilled water and adding a single drop of 98% acetic acid. Then, one drop of abdominal or pleural effusion is added. If the drop dissipates, the test is negative. If the drop retains its shape, the test is positive. A negative Rivalta's test is 97% accurate in ruling out FIP. A positive test is 86% accurate in ruling in FIP. Lastly, the pleural or ascitic fluid can be checked for protein, with FIP infectious fluid generally having a value of 3.5 mg/ dl or higher.

At necropsy, the wet form of FIP is characterized by a viscous yellowish fluid which generally clots soon after the abdomen is opened. The serosal surfaces of the intestine, kidneys, liver, and pancreas are often covered to varying degrees with small white nodules. These nodules represent pyogranulomas, accumulations of macrophages and neutrophils. This reaction is more common to fungal infections than to viral ones. In fact, fungal infections such as histoplamosis, cryptococcosis, blastomycosis, and coccidiomycosis must be considered as part of the differential. To defInitively diagnosis FIP, immunohistochemistry staining (IHC) of affected organs is necessary. In IHC staining, antibodies specifIc for the feline coronavirus are attached to a stain and exposed to the affected tissue. If coronavirus is present in the lesion, the antibody will stick and so will the stain, confIrming FIP infection.

Figure 1: The abdomen is fIlled with copious amounts of a clear but viscous yellowish fluid

.... ~ with tags of fIbrin throughout.

Figure 2: Soon after opening the cavity, the fluid has clotted.

29


FELINE INFECTIOUS PERITONITIS (continued)

Figure 3: Small white nodular lesions on the serosal surfaces of the small intestine. Microscopically these nodules feature accumulations of macrophages and neutrophils.

Figure 5: Small nodules and tags of clotted fluid cling to the surface of the spleen.

Figure 4: Small nodules and tags of clotted fluid cling to the surface of the liver.

Figure 6: Small white raised nodular lesions (pyogranulomas) are evident in the parenchyma of both kidneys.

, ;

30


MALPOSITIONS Volvulus/torsion involves a twisting of the mesenteric attachments of the stomach and/ or intestines. This twisting action cuts off the outflow of blood from the intestine and stomach, causing the tissues to suffer from a buildup of carbon dioxide and, eventually, a lack of oxygen. A common consequence seen is bloating (gaseous dilation) of the stomach. The twisting also pulls the spleen from the left side of the body to the right side and causes it to be engorged with blood.

Sometimes the intestine will telescope in on itself. This is called an intussusception. The blood supply draining the telescoped portion is cut off so the cells die from lack of oxygen. Occasionally in strong trauma cases (such a hit by car) the diaphragm will rupture allowing the intestines to move up into the chest cavity (diaphragmatic hernia). These abdominal organs interfere with the normal functioning of the heart and lungs.

Figure 1: Large congested spleen evident on the right side of the body caused by rotation of the stomach. .

Figure 3: Section of gut telescoped on itself :ntussusception) . The telescoping cuts off

- enous drainage from the affected area and ~e effect on the tissue is identical to a :;)[sion.

Figure 2 : Gas-filled and hemorrhagic stomach subsequent to gastric torsion/volvulus .

Figure 4: Localized intestinal torsion.

31


STEP 5: OPENING AND EXAMINING THE THORACIC CAVITY

The thoracic cavity or the abdominal cavity can be opened next. When opening the thoracic cavity, first cut the right ribs dorsally a few inches below their vertebral attachments using bone shears. Next, cut along the costo-chondral junction. The rib cage can then be removed by cutting any remaining muscle or soft tissues. Removal of the rib cage exposes the thoracic organs in situ.

Upon opening the thoracic cavity, make note of any fluid in the chest or in the pericardial sac. Blood in the thoracic cavity is called hemothorax. If there is fluid in the chest cavity that is not blood, the term is hydrothorax or pleural effusion. If the fluid is not blood, but is red because it is "blood-tinged", it is described as serosanguinous.

Rib .cage

Figure 1: The ribs are cut along the costochondral junction and near their dorsal spinal attachments

When air is present in the thorax it is called a pneumothorax and the lungs will usually be partially collapsed. If air builds to positive pressure inside the thorax, it is called a tension pneumothorax, and the lungs are usually fully collapsed (atelectic).

Figure 2: Normal heart and lungs exposed after removing the rib cage

Figure 3: Blood accumulation in the thoracic cavity (hemothorax)

r

r ;

32


Figure 4: Serosanguinous fluid in the thorax (hydrothorax/pleural effusion). Though the fluid is red, it is evident that it is translucent and not thick enough to be actual blood.

Figure 6: Here the chest cavity is filled with a -;-ery thick red exudate (often called a "tomato soup" exudate) consistent with blood-tinged .!Jus (pyothorax) caused by Nocardia.

Figure 5: Milky white fluid in the thoracic cavity (chylothorax). This condition is usually seen in association with cardiomyopathy, and rarely, (although it is a common misconception) due to thoracic duct rupture.

Figure 7: Much of the intestines have migrated into the thoracic cavity via a hole in the diaphragm (diaphragmatic hernia). The negative pressure in the thorax facilitates the movement of intestines into the thorax even through very small openings.

33

-


STEP 6: REMOVING THE HEART AND LUNGS

The esophagus should be separated from the trachea and is reflected to the point where it goes through the diaphragm into the stomach. The aorta and vena cava are cut and the trachea, heart, and lungs ("the pluck") are removed en masse. The trachea should be opened and followed as far irito the bronchi as possible. Foamy fluid in the bronchi or trachea indicates pulmonary edema.

Figure 1: The esophagus is separated from the trachea back to the diaphragm

Figure 3: Normal, uncongested lungs

The external color of the lungs should be assessed and all lobes palpated for firmness and/or nodular lesions. At necropsy, the appearance of "normal" lungs can vary from an uncongested pale light pink, to an irregular splotchy reddened congestion. Other grossly evident findings include hemorrhage, edema, neoplasia, and pneumonia.

Figure 2: The heart and lungs (the "pluck") removed

'. "

/ ', .. 'l""

Figure 4: Normal uncongested lungs (microscopic)

I /

""..... 4 .. ..l.. ....

, " ~;.; :,~ -:: ~!

, .

; '. ~;.... ~/ ' .~ .. f "

jjO

34

.hapter 3 The Necropsy Procedure

Figure 5: Normal, irregularly congested lungs

Figure 7: Foamy tracheobronchial fluid = dicative of pulmonary edema

Figure 9: Pulmonary atelectasis

Figure 6: Normal congested lungs (microscopic). The vasculature is distended with blood but the alveoli are clear

Figure 8: Pulmonary edema (microscopic). Many alveoli contain eosinophilic staining fluid.

Figure 10: Pulmonary atelectasis (microscopic). The alveoli are devoid of air and 35 collapsed.

Figure 11: Pulmonary emphysema

Figure 13: Pulmonary hemorrhage

Figure 12 : Pulmonary emphysema (microscopic) . The alveoli are dilated, ruptured, and coalescing. .

Figure 14: Pulmonary hemorrhage (microscopic). The alveoli are filled with blood with no significant inflammation. Non-inflammatory pUlmonary hemorrhage may result from pulmonary thromboembolism, lung lobe torsion, or coagulopathy.

Figure 15: "The Float Test" is used to help determine the presence of common lung conditions at necropsy. When placed in fluid (fixative or water), normal aerated lungs (congested or non-congested) will float on the surface. Lungs with pneumonia or that are atelectic will sink to the bottom. Fluid-filled lungs (pulmonary edema) will "float heavy", suspended somewhere between the surface and the bottom. This picture illustrates all three examples .

36


PNEUMONIA Pneumonia is inflammation of the lungs. It is characterized by the accumulation of inflammatory cells and fluid within alveoli. Grossly, it can be difficult to distinguish ':Jetween inflammation from physiological or passive congestion of the lungs since both ::eature a reddening of the lung parenchyma.

hree gross characteristics of pneumonia can ~elp in distinguishing the two. First, since pneumonia is usually caused by bacteria which enter the lungs via the trachea (bronchopneumonia), the inflammation starts ';1;'here the bacteria initially settle in the lungs.

Figure 1: Gross bronchopneumonia. Note :he pattern of reddening in the anterior and 7entral regions of the lung lobes

Figure 3: Pneumonia (microscopic). Note :..'-1e presence of inflammatory cells filling the " veoli. Palpation of this tissue would result in ?. firm feel, and there is no air to allow it to ::'oat when placed in liquid.

This is usually the anterior and ventral regions of the lungs, giving the reddening an "antero-ventral" distribution. Non-inflammatory congestion is irregular and/ or diffuse. Second, because of the accumulation of inflammatory cells in the alveoli, there is little or no air in the alveoli, reSUlting in a firm feel to the parenchyma (consolidation). Third, the lack of air in the lungs in pneumonia causes the lungs to sink when placed in water or fixative, whereas congested lungs will still float.

Figure 2: Gross bronchopneumonia. Note the pattern of reddening in the anterior and ventral regions of the lung lobes

Figure 4: Close-up of pneumonia lung. The alveoli are filled with inflammatory cells and devoid of air.

1

37

--- .. --------------------------------------------------------------------------------------------------~ . .--Chapter 3 The Necropsy Procedure

STEP 7: OPENING AND EXAMINING THE HEART

The outer surface of the heart should be examined before opening. Assess the sharpness of the apex; rounding may suggest hypertrophy or dilation. If a scale is available, the heart should be weighed. The normal heart weight (g) to body weight (kg) ratio is 7.4 0.2 however, care must be taken when interpreting this number as certain factors can affect the formula. In a fat or obese animal, the ratio will be skewed low, where as in a thin or emaciated animal it will be skewed high.

One of the most widely accepted methods of opening the heart is by following the normal path of blood flow. Beginning in the caudal vena cava and/or entrance to the right atrium, a V-shaped incision is made by cutting down through the right atrio-ventricular valve, following the inter-ventricular septum to the bottom of the ventricle, then back to the base of the heart and out through the pulmonary valve. This cut produces a V -shaped flap which can be lifted to expose the right ventricle, right atrium, and tricuspid valve.

The left side of the heart is opened in a similar way. A single incision is made through the left atrial free wall, down through the lateral border of mitral valve and the left ventricular free wall all the way down to the apex. A cut is then made through the medial leaves of the mitral valve into and out of the aorta.

Sometimes a better in situ visualization of the valves, as well as an opportunity to compare the relative thickness of the right and left ventricular myocardium, can be determined by doing a single longitudinal cut. The cut starts through the middle of the right ventricle and proceeds through the RV lumen, the interventricular septum, the LV lumen, and finally through the LV free wall.

Figure 3: To open the right side of the heart, cut into the right atrium via the vena cava, then down through the tricuspid valve to the bottom of the right ventricle.

Figure 1: Grossly normal heart. Note the sharp apex.

Figure 2: Very rounded apex indicating either hypertrophy or dilation

Figure 4: Cut along the septum and exit the right ventricle through the pulmonary artery.

r ;

38

hapter 3 The Necropsy Procedure

Figure 5: The flap produced allows visualization of the right atrium, ventricle, and rricuspid valve.

Figure 7: Cut through the mitral valve to exit :...'-1e left ventricle through the aorta.

Figure 6 : To open the left heart, cut into the left atrium via the pulmonary veins and continue the cut through the mitral valve and along the free wall to the bottom of the left ventricle .

Figure 8: Alternatively, by lining up on the middle of the right ventricle, a single cut through the right ventricle, interventricular septum, and the left ventricle will allow a better comparative visualization of the chambers. In this normal heart, note the 3: 1 ratio of left ventricular thickness to right ventricular thickness. Also note the relatively tubular shape of the left ventricular lumen, not a round or bowl shape as is the popular miscoriception.

39


Figure 9: The nodular thickening noted in the mitral valve of this partially fIxed heart is Valvular Endocardiosis (Degenerative Mitral Valve Disease). In this condition, the heart valve (usually the mitral) is thickened by the proliferation of the valve's fIbrous and myxomatous tissue. This proliferation distorts the leaves of the valve, giving them a nodular appearance. This change is usually mild and is a common incidental fInding at necropsy of no clinical consequence. It can get worse with age, however, and can be signifIcant in older dogs. When severe, the valves do not close properly and blood regurgitates into the left atrium on systole (causing a systolic murmur). The eventual consequence of this regurgitation is chronic heart failure . King Charles Cavalier Spaniels have a very high genetic disposition to develop this condition at an early age.

Figure 11: Severe left ventricular dilation. There is thinning of the free wall and septum and smoothing of the endocardial surface. The lumen shape is more bowl-like as opposed to a more normal tubular shape.

Figure 10: Severe left ventricular hypertrophy is evident in this partially fIxed heart. The lumen is extremely narrowed by the marked thickening of the septum and free wall. Cardiomyopathy (with a big C) refers to primary cardiac disease in which some inherent (and idiopathic) defect in the heart muscle itself results in hypertrophy or dilation of the myocardium (Hypertrophic or Dilative Cardiomyopathy). Secondary dilation or hypertrophy (due to valvular defects, septal defects, hypertension, etc.) does not constitute Cardiomyopathy.

Figure 12: Heart-based tumor (chemodectoma)

40

a !UM


Figure 13: Metastatic thyroid carcinoma

Figure 15: Small metal projectile (bb) ?enetrated the heart and lungs causing marked ::::'emorrhage

Figure 14: Metastatic salivary gland carcinoma

Figure 16: Subendocardial hemorrhage on the papillary muscle

41

..


THROMBOSIS vs. POSTMORTEM CLOTTING During the necropsy examination, differentiating postmortem clotting from antemortem clotting is very important. Clots are common in the heart and larger vessels. Thrombi are always pathological and significant, while postmortem clots hold no significance.

The normal clotting mechanism in the living animal leads to the formation of fibrin to plug openings in blood vessels to prevent bleeding. When clotting occurs within the vascular system in response to endothelial injury, the resulting clot is called a thrombus and can block blood flow to tissues and cause necrosis (infarction). Blood also clots after death in response to the release of tissue factors. These are called postmortem clots. Distinguishing antemortem clots (thrombi) that are important in causing disease from postmortem clots that are of no significance is important during necropsy. Even though they are both clots, the mechanism of their formation makes them physically distinguishable from each other. Postmortem clots form as a solid net of fibrin within the vessel, entrapping large numbers of red blood cells. Consequently postmortem clots are dark red in color, they have a gelatinous consistency, and are smooth, wet and shiny. They are also usually well-molded to the shape of the vessel. Thrombi are formed by the sequential deposition of platelets and fibrin, forming a layered effect without the incorporation of significant numbers of red cells. Consequently thrombi have a friable ("crumbly like a cookie") consistency, and have a paler, drier, rougher appearance. Because of this friability, pieces easily break off the main thrombi and float down the bloodstream as a thromboembolus, and can lodge in smaller vessels, block blood flow, and cause an infarct.

Two different types of postmortem clots can occur after death. The most common type is called a "currant jelly" clot. This is the very common, red, shiny, and smooth gelatinous clot. If clotting is delayed for some reason after death, the stagnant blood will have a chance to separate (the red cells settle to the bottom), leaving a yellowish layer of plasma at the top. When clotting ultimately occurs, a currant jelly clot is formed at the bottom, and a plasma clot (called a "chickenjat clot") is formed at the top. The appearance of chicken fat clots in most animals denotes a possible clotting disorder since postmortem clotting was delayed. Horse red blood cells, however, normally settle rapidly due to rouleaux formation so chicken fat clots in horse are inconsequential.

Figure 1: Two "currant jelly" postmortem clots within the heart chambers. Note the smooth dark red, shiny, and gelatinous appearance.

Figure 2: Microscopically, currant jelly postmortem clots consists almost exclusively of red blood cells with a few entrapped white blood cells. Fibrin is usually not clearly recognizable.

Figure 3: In this heart, both a currant jelly clot and a chicken fat clot are evident. -Both are postmortem clots.

,

42

hapter 3 The Necropsy Procedure

THROMBOSIS vs. POSTMORTEM CLOTTING (continued)

Figure 4: Two thrombi attached to the mitral valve. Valvular thrombi are often caused by bacterial endocardial damage and constitutes "vegetative endocarditis".

Figure 7: Viewed here is an opened left pUlmonary artery containing one leg of a s addle thrombus (arrows) . The thrombus started at the junction of the pulmonary trunk then extended into the lungs along each branch (pulmonary thromboembolism).

Figure 5: A thrombus attached to the aortic valve. Note the pale, dull and rough appearance.

Figure 6: Microscopically, thrombi often have a layered appearance (called "Lines of Zahn"). Here, a thrombus nearly occludes a blood vessel. The dark purple blobs are bacteria (this is a "septic" thrombus)

43


STEP 8: REMOVAL AND EXAMINATION OF THE LIVER

After removal of heart, lungs, and the diaphragm, the abdominal viscera can be removed systematically, starting with the liver. Before removal of the liver, the bile duct connection to the duodenum should be checked for patency. Make a small slit in the proximal duodenum and identify the major duodenal papilla. Squeeze the gallbladder to see if bile can be easily expressed through the duct and out the papilla. If not, the bile duct should be opened and traced back up to the gallbladder. The liver can then be removed by cutting the bile duct and all diaphragmatic and body wall connections.

After removal of the liver, the size, conformation, and color should be assessed.

Figure 1: The bile duct is checked for patency. As the gallbladder is squeezed, note the stream of bile from major duodenal papilla (arrow)

Figure 3: Focal area of hepatic necrosis

Alternating pale and dark areas can produce a "reticulated" or "nutmeg" appearance. Prominent fat infiltration can produce a very yellowish liver. Obviously, any masses or nodules should be noted.

After assessing the surface, the liver should be "bread-loafed", cut into small 1-2cm slices from end to end, to expose possible lesions deep within the pencltyma that are not visible on ,the surf~c~,/fhe gallbladder should be opened to assess the character of the bile, the presence of any stones or concretions, and the possibility of hyperplasia or neoplasia of the gallbladder epithelium.

Figure 2: Grossly normal liver

Figure 4: Severe hepatic lipidosis 44


Figure 5: Hepatic nodular hyperplasia

Figure 7: Gallstone in the gallbladder

Figure 9: Metastatic hemangiosarcoma

Figure 6: Nutdleg liver (chronic passive congestion)

Figure 8: Hepatic biliary adenocarcinoma

Figure 10: Hepatocellular carcinoma 45


NECROSIS Necrosis is common in the liver and other tissues and must be properly identified and categorized when it occurs.

Necrosis is the death of cells within the body that occurs prior to somatic death (death of the animal). It can be recognized both grossly and microscopically, and varies depending on the type of necrosis. The types of necrosis are coagulative, caseous, and liquefactive.

Coagulative necrosis is defined as necrosis where cellular and/ or tissue architecture is preserved (the cells still look like cells). Grossly, coagulative necrosis is usually characterized by a distinct paleness of the tissue. Depending on the degree of hemorrhage present, the tissue may be red or might have a red border. One of the most common causes of coagulative necrosis is hypoxia/ischemia, which in turn is often due to loss of blood supply. An area of necrosis due to hypoxia is called an infarct. Microscopically, coagulative necrosis is characterized by dead cells, recognizable due to distinct nuclear changes. The nuclear changes that represent undeniable cell death 'are pyknosis, karyorrhexis, and karyolysis. Pyknotic nuclei are shrunken, dense and dark. Karyorrhectic nuclei are fragmented into several pieces. Karyolytic nuclei have lost much of their dark staining, resulting in either a pale

Figure 1: The pale regions of this muscle are necrotic. Aside from the color change, the tissue architecture is still present (the affected areas still look like muscle) so this would be coagulative necrosis.

nucleus or no nucleus at all. Caseous necrosis is necrosis where the dead tissue is still present but has degenerated into an unrecognizable matrix. Grossly, caseous necrosis has a dry, cottage cheese-like appearance and texture. Microscopically, caseous necrosis is a eosinophilic granular material with no recognizable cells. Certain types of bacteria are often the cause of caseous necrosis including

/::: b . Myc~bacterium and somf Coryne actenum speCles. ~/

Liquefactive necrosis is necrosis where the tissue cells have been completely liquefied, leaving only fluid, inflammatory cells, and possibly the causative agent. Liquefactive . . necrosis is the most common type of necrOS1S m the brain due to the high water and lipid content. In other tissues, liquefactive necrosis usually only occurs due to infections by certain bacteria with very powerful enzymes which can liquefy tissue ("pyogenic" bacteria). Because of these bacteria, neutrophils are generally present in high numbers within the liquefied tissue. Grossly, liquefactive necrosis is characterized by a cavity filled with a creamy white, viscous, and often foul-smelling fluid (pus). When this cavity is well-defined and walled off with connective tissue, it is referred to as an abscess. Microscopically, no tissue cells are present, only the neutrophils and the bacteria.

nuclear changes

pyknosis

karyorrhexis

normal

karyolysis

Figure 2: Microscopically, cell death in coagulative necrosis is identified primarily by t~e presence of particular nuclear changes (pyknOS1S, karyorrhexis, and/or karyolysis). These changes occur together but independently in the same tissue and do not represent a continuum (ie.

, ,

karyorrhexis does not follow pyknosis, etc.). 46

'f'

vhapter 3 The Necropsy Procedure

.NECROSIS (continued)

Figure 3: Coagulative necrosis. The cortex :eatures mUltiple infarcts, roughly triangular pale regions bordered by a thin zone of red ~emorrhage

Figure 5: Coagulative necrosis. Clear 3idence of cell death is apparent (pyknotic ",--'1d karyorrhectic nuclei), but the cellular :;:-chitecture is still intact

Figure 4: Microscopic coagulative necrosis of the liver. Many necrotic cells have pyknotic nuclei (white arrow) and karyolytic nuclei (green arrow). There is also an increased cytoplasmic eosinophilia and vacuolization, however cellular architecture is still maintained .

Figure 6: Coagulative necrosis can also represent preservation of,tissue detaiL In this kidney, renal tubular cells are unrecognizable however the tissue/tubular shape (architecture) is preserved.

47


NECROSIS (continued)

Figure 7: Grossly, caseous necrosis has a dry, granular, "cottage cheese-like" consistency.

Figure 9: Grossly liquefactive necrosis is often characterized by a well-circumscribed walled-off cavity containing a creamy pale foul-smelling viscous liquid (pus) forming an abscess.

Figure 8: Microscopically, caseous necrosis is generally a pink, amorphous matrix with no recognizable cells or cellular structure

Figure 10: Microscopically liquefactive necrosis features completely loss (liquefaction) of the parenchymal tissue, with only inflammatory cells (usually neutrophils) remaining.

48

hapte r 3 The Necropsy Procedure

NECROSIS (continued)

~e microscopic pattern of necrosis in an organ :;.an be helpful in determining the cause. In the iver, necrosis can occur randomly throughout ::he liver, or in one of three zones of the hepatic ~obule.

~andom necrosis of the liver is usually associated with infectious organs which gain access to the liver via the vascular system. This ~7pe of necrosis is usually associated with :""-illammation, though some viral infection may ':Je non-inflammatory.

?atterns of necrosis of the hepatic lobule are ::he result of its microanatomy and function. ~e hepatic lobule is an irregular hexagonal structure with a large vein at the center (the ~entral vein) and portal regions at the :;>eriphery. The portal regions consist of the ::epatic artery (bringing oxygenated blood to the iver), the hepatic vein (bring unoxygenated but

u trient-rich blood from the GI tract), and a bile Qu ct. Oxygenated blood which enters via the i epatic artery drains through the sinusoidal sp aces into the central vein, where it is eventually dumped into the vena cava. Because :..~e hepatocytes around the central veins are ::ne last to receive oxygenated blood, they are extremely susceptible to hypoxia and anemia,

Figure 1 1: Centrilobular hepatic necrosis

Centrilobular necrosis is most commonly associated with anemia of any cause, or with passive congestion of the liver due to righ t sided heart failure. Centrilobu lar hepatocytes a lso contain the highest concentrations of mixed function oxidases (MFOs). MFOs are enzymes responsible for the metabolism of chemical substances in the blood. Metabolism of some substances may produce toxic metabolites which may in turn cause degeneration and necrosis of the centrilobular hepatocytes. Substances which can cause this pattern of necrosis include acetaminophen and aspirin.

Mid-zonal necrosis, necrosis in region of the hepatic lobular between the centrilobular region and the periportal region, is uncommon but is seen in rare toxicities (like hexacholorophene in cats).

Periportal necrosis occurs in toxicities where the toxin does not require metabolism by MFOs, but is already toxic when it enters the liver through the hepatic artery or vein. Because the periportal hepatocytes are the first affected, they suffer more degeneration and necrosis than the mid-zonal or centrilobular regions. This pattern of necrosis can be seen in cer tain poisonous, alkaloid-containing plants.

Figure 12: Periportal hepatic necrosis and fibrosis .

49


STEP 9: OPENING AND EXAMINING OF THE INTESTINE

The esophagus, stomach, small intestine, large intestine, pancreas, and spleen are removed en masse by cutting the diaphragm and the root of the mesentery. The colon is typically cut as it passes into the pelvic canal. If pathology is suspected in the pelvic canal, it is opened by cutting the pubic and ischial bones on both sides, allowing the removal of the floor of the pelvis.

Once the viscera is removed, the spleen is cut away and set aside for later examination. The pancreas is also examined, cut away from its duodenal attachments and examined.

Figure 1: Remove the GI tract by cutting the root of the mesentery (marked by the scissors)

Figure 3: Full GI tract. These small intestines are thickened, hyperemic, and have a slightly pitted surface, all evidence of inflammation.

To facilitate opening of the gastrointestinal (GI) tract, all of the mesentery is cut away from the bowel loops, thereby allowing the entire tract to be laid out straight. Opening starts in the esophagus, proceeds along the greater curvature of the stomach, and extends throughout the length of the small and large intestiI}e. -Stomach and intestinal contents-are assess~d, along with the surface mucosa. Any foreign o,bjects and/ or parasites should be identified -and their possible impact on gastrointestinal function assessed. The entire t r:act should be assessed for inflammation, ulceration, thickening, and/or neoplasia.

Figure 2: When necessary, open the pelvis by cutting the pubic (white arrow) and ischial bones (green arrow) on each side to remove the floor of the pelvic canal.

Figure 4: The mesentery has been cut away to facilitate opening the intestines.

50


Figure 5: The intestine and liver are knotted together in a tight ball by fibrin (fibrinous peritonitis)

Figure 7: Roundworms (Toxocara canis) in the small intestine

Figure 9: Severely hemorrhagic intestine 'Parvoviral Enteritis)

Figure 6: Multifocal petechial hemorrhaging in the mucosa of the small intestine due to hookworms (Ancyclostoma caninum).

Figure 8: Whipworms (Tricuris vulpis) in the large intestine

Figure 10: Hemorrhagic mucosal surface of jejunum (Parvoviral Enteritis) 51

~~------------------------------------------------------------------------------------------------~- -


Figure 11: Markedly thickened cross-section of small intestine with multifocal pale yellow necrotic regions . Microscopically, there was prominent pyogranulomatous and necrotizing enteritis with large numbers of hyphal fungal organisms (Phycomycosis)

Figure 13: Thickened region of the jejunum with focal perforation and leakage of intestinal contents.

Figure 12: Neurofibrosarcoma on the colon

Figure 14: Section of intestine from Figure 13 opened up. Microscopically there was an infiltration of neoplastic lymphocytes (lymphosarcoma) which weakened the wall and led to the perforation.

52


Figure 15: Severe esophageal inflammation and ulceration from gastric reflux (Gastro-esophageal Reflux Disease or GERD)

Figure 17: Gastric foreign body

Figure 19: This stomach was filled with clearly recognizable pieces of sausage. This was :1ot deemed important until considered with :he history. The owner stated that she fed the animal a strict commercial dog food diet. This ~ade the presence of sausage suspicious. The animal had died acutely with no clinical signs. Closer inspection of the sausage revealed small :?ellets (see insert) consistent with Strychnine :?ellets . Subsequent t~xicology was positive for ""'trychnine. The history was pivotal in this ::ase as it affected the consideration of a seemingly benign finding.

Figure 16 : Multifocal gastric ulcerations and hemorrhage (injudicious NSAIDS use)

Figure 18: Gastric mucosal calcification due to renal failure.

53


STEP 10: EXAMINATION OF THE PANCREAS

Changes involving the pancreas include inflammation, hemorrhage, and neoplasia. When acute, pancreatitis is often hemorrhagic, however hemorrhage can be an agonal change so interpretation grossly is tentative unless supported by accompanying lesions. Acute pancreatitis is characterized by loss (necrosis) of pancreatic tissue, as well as varying degrees of necrosis of the surrounding tissues. The peri-pancreatitic fat is commonly involved and the result is saponification, the formation of soap due to the action of the strongly alkaline enzymes leaking from the pancreas on the fat . This generally appears as white plaques within the fat. When pancreatitis is chronic, the gland is generally very nodular in

Figure 1: Grossly normal pancreas

Figure 3 : Chronic pancreatitis

appearance due to the formation of prominent connective tissue, as well as due to regenerative nodules.

There are numerous possible causes of pancreatitis. Nutritional factors believed to contribute tOiJancreatic acinar-cell injury include obesity, h igh fat diets, and hyper1ipoprotein~mia. Drugs are also suspected of causing some cases of pancreatitis an these include su1fonamides, tetracycline, and corticosteroids. Surgical manipulation, blunt abdominal trauma, and biliary tract diseases have also been implicated.

Figure 2 : Marked pancreatic hemorrhage and edema (acute pancreatitis)

r

(j

Figure 4: Pancreatitis with fat sap'onification. Note the white plaques in the adipose tissue.

54


STEP 11: REMOVAL & EXAMINATION OF THE SPLEEN

The spleen should be examined for its size, shape and conformation. A normal spleen can be either contracted or congested at necropsy, although contracted is most common. The contracted spleen has a lightly brownish hue, often with wrinkling of the capsule. The congested spleen is very dark red, with a smooth taut outer surface and a gelatinous cut su

color atlas of small animal necropsy 1

Documents