necropsy techniques in reptiles part 1: general introduction and lizards and crocodilians

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  • waiting for the post-mortem examination. Freezingshould be always be avoided in order to preventartefacts resulting from the freezing procedure.Freezing should only be used if there is no othermeans of refrigeration or if ancillary procedures(virus isolation, PCR, etc.) will be hampered by aprolonged post-mortem interval. Small carcasses willcool down faster than larger ones and adequatehistological preparations can be obtained even afterseveral days of refrigeration.

    Carcasses in advanced stages of decomposition can bestill examined and prominent macroscopic lesionscan be still detected. Tissues from decomposedanimals can be collected for toxicologicalexamination, although histological evaluation ofmost tissues may be compromised and in some casesnon diagnostic.

    If the body needs to be sent to a pathologylaboratory for examination ensure that the body iskept cold during shipping and is well insulated toslow down autolysis. If the necropsy is done by theclinician and only selected formalin fixed tissuesamples are to be sent out for examination, ensurethat the container is water tight and sealed to preventformalin spillage. In addition, all informationregarding the submitted case should be shipped withthe carcass or formalin fixed tissues in a separate,sealed, waterproof bag. Packaging must conform topostal regulations and remaining tissues/carcass mustbe disposed of appropriately.

    EQUIPMENT

    For reptiles it is important to have specificknowledge about the anatomy and physiology of theanimal that will be necropsied post-mortem. Anecropsy usually requires a small set of easilyobtainable equipment: scissors (different sizes), scalpelblades, forceps (different sizes), a ruler, a bone cutter,a cast cutting saw (i.e. Stryker) and/or a rotary tool(i.e. Dremel), microbial culturettes, sterilecontainers, labelling tags and or plastic embeddingcassettes, latex gloves, face masks, microscope glassslides (for smears and impression smears) andformalin containers (Fig. 1).

    INTRODUCTION

    Historically, reptiles have been viewed as unusual andunpleasant animals. Despite these mistaken beliefs,the last four decades have shown that both thescientific community including herpetologists,veterinarians, and biologists, and the people adoptingreptiles as pets or objects of collections have steadilygrown. Along with the increased interest in theseanimals as pets, the number of specialisedveterinarians working predominantly or exclusivelywith reptiles has also flourished. Although greatstrides have been taken in the understanding ofreptile husbandry, physiology, medicine and surgery,many diseases are still not well understood, easilytreated, or easily diagnosed. In some cases the onlyway to obtain a definitive diagnosis is with athorough necropsy, particularly when animals arefound dead with no previous clinical signs.

    A necropsy is the examination of a cadaver todetermine or confirm the cause of death and is alsocalled a post-mortem examination. A necropsy is anunfortunate event, but is an extremely valuablesource of information and opportunity for learning.There are several reasons for performing a necropsy,other than just as a diagnostic procedure. In aveterinary teaching hospital necropsies can also beused for teaching normal reptile anatomy,comparative anatomy, and even reptile physiology.Practitioners, students, herpetologists and pathologistcan also learn about disease processes from a reptilenecropsy. By observing the final result of a disease,more can be learned about ante-mortem diagnosisand potential treatment for the next clinical case.Because so much valuable information can be lostfrom a poorly performed reptile necropsy, it isimportant to understand how to preserve and be ableto systematically examine a reptile cadaver.

    PRESERVATION OF THE CARCASS

    The ideal necropsy should be performed on a freshcarcass soon after the death of the animal, in order toavoid post-mortem artefacts related to the decayprocess (autolysis). More often, however, many hoursto days will pass before the body can be examined. Inthese cases the animal should be refrigerated while

    SMALL ANIMAL EXOTICS UK Vet - Vol 15 No 5 June 2010 1

    Raffaele Melidone DVM, Christopher J. Gibson VMDTUFTS CUMMINGS SCHOOL OF VETERINARY MEDICINE, 200 WESTBORO ROAD,NORTH GRAFTON, MASSACHUSETTS.

    Necropsy techniques in reptiles Part 1: General introduction and Lizards and Crocodilians

  • WHAT MAKES A GOOD NECROPSY?

    A complete, accurate necropsy starts with thecollation of all available information for the animalto be examined, including radiographs, blood work,surgical reports, an accurate medical history,biological and environmental information (especiallyfor reptiles with specific environmentalrequirements), medical treatments if any, and aclinical diagnosis or suspected cause of illness ifpossible.

    In addition, the clinician submitting the animalshould have in mind and ask a few specific questionsthat he/she would like addressed during the postmortem examination.

    Every complete necropsy starts with a thoroughexternal examination including examination of theskin, shell, oral cavity, cloacal opening, ears, eyes andpalpation of bones (Figs. 2a and 2b). All biologicalmeasurements should be accurately taken andrecorded including body weight, organ weights, fluidvolumes, and the sizes and locations of all lesions.Careful dissection and gentle tissue handling isextremely important for smaller animals. Accuratedescription of the macroscopic findings, withpictures, will help recall the post-mortem findingslater and facilitate easy communication with othersthat were not present at the original necropsy.Representative samples of all tissue should be placed

    SMALL ANIMAL EXOTICS UK Vet - Vol 15 No 5 June 20102

    immediately in 10% buffered formalin and/or frozenfor toxicological or other ancillary tests. Blood,urine, gastrointestinal contents, and exudates can alsobe frozen if required for further investigations.Bacterial cultures should be taken aseptically andsubmitted as soon as possible for accurate results.

    A complete, well performed necropsy can provide anenormous amount of information and lead to anaccurate diagnosis. In contrast, a poorly performednecropsy will be likely to result in frustration and amissed diagnosis.

    NECROPSY TECHNIQUES AND INTERNAL

    EXAMINATION

    With the anatomical differences between reptilespecies, the post-mortem examination of reptiles canbe divided into three different groups, each of whichwith slightly different dissection techniques andanatomical features.

    Before starting a post-mortem examination inreptiles, it is important to know that reptiles mayhave prolonged contractions of the skeletal andcardiac muscles, even a few hours after death. Thiscan sometimes be disturbing for the veterinarianperforming the necropsy and any observers. It is alsoimportant to ensure that the animal is truly deadbefore starting a necropsy. In some cases, especiallylarge reptiles, it may be difficult to assess death if rigormortis has not yet occurred or if it has completelyfinished. Some pathologists and veterinarians may liketo ensure that the animal is dead by exsanguinatingthe animal prior to starting the dissection.

    LIZARDS AND CROCODILIANS

    Lizards and crocodilians have a similar body shapeand can be examined in dorsal recumbency.However, some lizards, such as chameleons, whichare laterally compressed, are better examined inlateral recumbency by removing the skin, underlyingmuscles and rib cage of one entire side of the animal,in order to expose the coelomic cavity (Fig 3).Extreme caution should be taken when examiningvenomous lizards (Heloderma spp., refer to venomoussnakes in subsequent article). Once the animal isplaced in dorsal recumbency two different incisions

    Fig. 1: Most tools necessary to perform a necropsyare easily retrievable in every veterinary clinic. Theplastic cassettes shown in the picture are useful whensampling small organs such as adrenal glands, thyroidsand parathyroids.

    Fig. 2a: Four digits of the right front limb are missingmost likely due to low environmental humidity andmoulting difficulties.

    Fig. 2b: Ball python with severe necro-suppurativestomatitis. (Photograph courtesy of Dr. Paolo SelleriCVS Rome.)

  • SMALL ANIMAL EXOTICS UK Vet - Vol 15 No 5 June 2010 3

    can be made to approach the coelomic cavity: eithera single incision is made on the ventral midline fromthe intermandibular region to the cloacal opening,or two ventrolateral incisions are made from the oralcommissures to the cloacal region. These incisionsshould follow the lateral margins of the ventralscales, removing the skin and underlying skeletalmuscles in one block (Figs. 4a and Fig. 4b).

    Access to the cranial coelom is gained by cutting the ribsand intercostal muscles at the costochondral junctionfrom the last ribs to the thoracic inlet, bilaterally (Fig. 5).Another incision should be made over the long axisof the medial aspect of the thigh to collect the sciaticnerve, which runs immediately parallel and caudal to thefemur, and a sample of bone with bone marrow fromthe proximal femur. Skin and skeletal muscle collectionsmay be also taken at this stage.

    The next step is to approach the oral/pharyngealregion in order to examine the oral cavity and freethe tongue, glottis and pharynx for examination andsampling. Two incisions should be made medially tothe mandibular rami through the skin (if still inplace) and intermandibular muscles extending intothe oral cavity. The resected tissues should bereflected caudally or laterally to visualise/examinethe tongue, oral cavity, pharynx, and larynx.Particular attention should be paid to theexamination of the gular valve in crocodiles, becauseit is a common site of diseases in these animals.Crocodiles have a pronounc

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