Basic Essentials of CNS Histopathology

(In Less Than 1 Megabyte)

Marie Beckner, MDUPMC Neuropathology

March 1, 2002

Please e-mail suggestions to:becknerme@msx.upmc.edu

Cell Lineage in the CNS

Neuroepithelial cell ingerminal zone

Ependymal cells

Astrocytes

Oligodendrocytes

Neurons

Peripheral blood

O2 Acells

Microglia

Mesenchymal cellsform blood vessels& meninges

Overview

Neurons: Morphology Stains Cellular responses InclusionsGlia: Astrocytes Oligodendrocytes Ependymal cells Microglia and macrophagesMeninges

Morphology of neurons, H&E

Projection neurons Granular cell neurons

Motor neurons large cell body nucleus with single large nucleolus prominent basophilic Nissl substance (RER & polyribosomes) axons & dendrites embedded in surrounding neuropil

Example of “local circuit” neuronsNaked nuclei seenLack Nissl substance

Neurons: Conventional Stains

Hematoxylin and Eosin (H&E) for general cytoarchitecture

Cresyl violet for staining Nissl substance

Silver stains (Bielschowsky & others) for staining axons and some inclusions

Many others but technically difficult and used less now that immunohistochemical stains are widely available

Neurons: Immunohistochemical Stains

Immunoperoxidase (ImP) or “brown” stains (can also be red, blue, black)

Neurofilament proteins: perikaryal (cell body) and axonal cytoplasm

Synaptophysin: vesicles at synapses so that punctate granular staining is seen diffusely in the neuropil and at the edges of neuronal bodies. Most useful and widely used.

Neuron specific enolase (NSE): non-specificOthers: Chromogranin, PGP9.5, -synuclein, NeuN, others (growing list)

Neurons: Cellular Responses

Cell body Chromatolysis Acute necrosis Atrophy Ballooning change Neuron loss

Neurons: Chromatolytic ChangesCentral chromatolysis (usual response to axonal damage that disrupts basic cell functions)

- loss of basophilic Nissl substance from central part of cell body, only at edges- enlargement of cell body with rounding

- nucleus displaced to periphery

- can also see in pellagra and Wernicke’s encephalopathy

Peripheral chromatolysis (loss of Nissl substance from the periphery (less common)

Neurons: Mimics of Central Chromatolysis

Large, normal neurons (Betz cells, mesen- cephalic nucleus of cranial nerve V)

Lipofuscin displacement of nucleus and Nissl substanceNeurons with eccentric nuclei (Clarke’s nucleus, paraventricular & supraoptic nuclei)

Diseases where neurons have displaced nuclei and Nissl substance (storage diseases and ganglion cell tumors)

Neurons: Acute Necrosis

Ischemic/hypoxic damage (6-8 hrs) leads to “red neurons” (not just bright pink)- Pronounced, eosinophilic cytoplasm- Shrunken cell body- Shrunken, darkly pyknotic nucleus that no longer contains a prominent, large nucleolus- Seen more easily in large neurons (vs. small)

Nonspecific finding that does notrule out malignancy in a biopsy.

Confused with “handling” artifact(cells have dark purple cytoplasm)

Neurons: Selective Vulnerabilities

Mature > immature neurons

Neurons > endothelial cells > glial cells

Regions of neurons: Hippocampal sclerosis (neuronsglia) - pyramidal neurons of hippocampal CA1 sector (susceptible) > CA2 sector Laminar necrosis - middle & deep cortical > superficial layer Sulcal depths Watershed areas

Neurons: Atrophy

Decrease in size of cell body and then loss (minimal & variable in aging)

Degenerative diseases (many)

Degeneration in response to injury 1. Retrograde (distal proximal) ex. Infarct in occipital visual cortex ipsilateral LGN neurons die

2. Transynaptic (neuron neuron) ex. Loss of retinal ganglion cells loss of neurons in LGNs

Neurons: Ballooning Change

Metabolic derangement undigestable product engorgement of cell body cell death

Lysosomal storage disorders Ex. Tay-Sachs disease Sandhoff Disease Nieman - Pick Disease

Neuron LossFinal common pathway for many conditions

Time course - acute or slow

Apoptosis - rapid nuclear fragmentation

Mineralization (Fe, Ca, etc.) may occur - very dark purple encrustation of dead neuron and/or axon - “ferrugination” - damaged axons with mineralization can resemble fungal hyphae - may see mineralized neurons adjacent to cystic cavities of remote infarcts

Neurons: Axonal Changes to Injury(1) Wallerian degeneration (proximal to distal) with or without degeneration of cell body

- beaded appearance of axon- injury of axon or cell bodyex. Nerve transection, metabolic injury, and ischemiaCNS - no reinnervation

(2) Retrograde degeneration (distal to proximal)-“Dying back” process- Metabolic derangement of entire neuron- Distal axon most vulnerable- Usually slow progressive clinical courseex. “Stocking glove” neuropathy in diabetes mellitus

Neurons: Axonal Changes to Injury(3) Focal axonal swelling (axonal spheroids, axonal retraction balls, axon torpedos for Purkinje cells)

- distended axons filled with neurofilaments & organelles- nonspecific response (disturbed metabolism)- etiologies include severe axonal injury (ischemia, trama, degenerative, normal aging)- rarely inherited (neuroaxonal dystrophy)- “Herring bodies” - storage of hormones in infundibulum and neurohypophysis

- normally seen in fasciculus gracilis in medulla with aging, may be mineralized

Neuronal Inclusions - Normal(1) Neuromelanin (starts around 5 yrs of age)

- By-product of tyrosine needed in cate-cholamine (dopamine & norepinephrine)synthesis- Substantia nigra, locus ceruleus, & dorsalmotor nucleus of vagus

- Abundant brown, cytoplasmic pigment(much darker than lipofuscin) on H&E- Lost in substantia nigra in Parkinson’s dz

Neuronal Inclusions - Normal

(2) Lipofuscin, “aging pigment”, common - golden brown on H&E in neurons & glia

- displaces cytoplasmic organelles and may mimic central chromatolysis- lipids, proteins, carbohydrates (PAS+)- grossly a mahogany hue (LGBs)

- lateral geniculate bodies (LGBs), inferior olives, dentate nuclei of cerebellum, and anterior horn cells of spinal cord

- rare inherited, fatal disease - Ceroid lipofuscinosis

Neuronal Inclusions - Normal

(3) Marinesco bodies- intranuclear, increase with age- small, multiple, no halos, no effacement of the nucleus, size of nucleolus- Cowdry type B (not viral !!)- immunoreactive for ubiquitin

- substantia nigra and locus ceruleus

Neuronal Inclusions - Normal

(4) Hyaline colloid inclusions - cytoplasmic, homogenous - hypoglossal nucleus (common) - anterior horn cells (rare) - dilated endoplasmic reticulum with amorphous material

(5) Eosinophilic inclusions of inferior olives - immunoreactive for ubiquitin

(6) Others - describe with diseases where they are increased

Neurons- Inclusions in Infection

Nuclear(1) Cowdry type A - Herpes simplex (HSV), herpes simiae Varicella zoster (VZV), cyto-megalovirus (CMV), measles virus (subacutesclerosing panencephalitis)

“owl’s eye”large, solitary, clear haloperipheral margination of nuclear chromatin

(2) Cowdry type B - anterior horn cells in poliomyelitis

(3) Ground glass - Herpes

Neurons - Inclusions in Infection cont.

Cytoplasmic Rabies - Negri bodies (Round, eosinophilic, hyaline, well-defined) - Lyssa bodies (Irregular, eosinophilic) - Most easily seen in hippocampal pyramidal cells or Purkinje cells

Viral antigen demonstrated also with immunostaining

Neurons - Pathologic inclusions, non- infectious diseases cont.(1) Neurofibrillary tangles (NFTs)

- many in Alzheimer’s disease but alsoseen in other degenerative conditions, a few in some older patients, and rarely in afew other conditions

NFTs assume shape of cell classically “flame” shape but may be round, “globoid”

H&E - faint basophilic wispsBielschowsky - dark brown, more prominentImmunoreactive for P-tau

Neurons - Pathologic inclusions cont.

(2) Granulovacuolar degeneration of Simchowicz - cytoplasmic, basophilic, dot-like granules in small clear vacuoles (resemble marbles)

- single or multiple (few to many)

- hippocampal pyramidal neurons

- few in older non-demented patients but may be extensive in Alzheimer’s disease

If more than occasionalrule out Alzheimer’sdisease

Neurons - Pathologic inclusions cont.

(3) Hirano bodies - Oval to elongated rod-shaped, eosinophilic - Cytoplasmic but may appear to be in neuropil

- Hippocampal pyramidal neurons, CA1 sector- Cytoskeletal elements including -actinin

- Few in normal elderly patients, increased in Alzheimer’s disease

Neurons - Pathologic Inclusions

(4) Lewy bodies: - Large, homogenous, eosinophilic, - Halos +/-, cytoplasmic

- Immunoreactive for -synuclein, ubiquitin, neurofilament, & crystallin- Parkinson’s disease - substantia nigra, locus ceruleus locations- Lewy body dementia - Cortical (more difficult to see without special stains

Neurons - Pathologic Inclusions cont.

(5) Pick bodies: - Cytoplasmic, round to oval, slightly basophilic and difficult to see on H&E

- In swollen neurons in Pick’s disease- Easily demonstrated with silver stains- Immunoreactive for P-tau, ubiquitin, neurofilament

H & E Bielschowsky

Neuronal Differentiation in TumorsNissl substance (RER) - Cresyl violet stainImP stains (synaptophysin, neurofilament, etc.)EM (dense - core vesicles, etc.)Neuronal tumor cell rosettes:

“True” rosette withcentral lumen

Flexner-Wintersteiner rosette(retinoblastomas and PNETs)

“Pseudorosette - nocentral lumen

Homer-Wright rosette(Neuroblastoma, Medulloblastoma,

PNETs)

Glia

Astrocytes (“star” cells)

Oligodendrocytes (“few branch glia”)

Ependymal cells Tanycytes Choroid plexus epithelium

Microglia

GFAP S100

+ +

- +

- ++ +- +

- -

AstrocytesH & E: Oval nuclei floating in a fibrillar matrix

GFAP or S100: Radiating cytoplasmic processes

Two main types: Fibrillary (white matter) - majority with numerous and extensive branches Protoplasmic (gray matter) - fewer branches

Subtypes - Bergman glia (cerebellar cortex)

- Pilocytic (periventricular, cerebellar, & spinal cord white matter)

GFAP + reactive astrocyte

Astrocytes - Cellular Responses

Gliosis - rapid primary reaction to CNS injury - can be chronic leading to dense fibrillary gliosis (CNS version of scar) - typical and special types - diffuse swelling of cortical astrocytes can contribute to the risk of edema (normally 1/3 volume of cerebral cortex)

Astrocytic reaction in progressive multifocal leukoencephalopathy (PML)

Inclusions

- bizarre nuclei with atypia that suggests a malignant astrocytoma

Gliosis continuedTypical - well-defined cytoplasm on H&E that is slightly to markedly increased. The distribution of reactive astrocytes is best seen with GFAP (brown, stellate) and is uniform. Gemistocytes are “stuffed cells” as shown.

Special types: - Bergman gliosis (seen around cerebellar infarcts) - Chaslin gliosis - subpial - Alzheimer type II (“empty” irregularly shaped nuclei, liver disease)

Astrocytes - Cellular ResponsesInclusions - Age related

Lipofuscin pigment accumulationCorpora amylacea (polyglucosan bodies)

- concentrically laminated basophilic spheres- glucose polymers in astrocytes (PAS +)- prominent accumulations subpial & perivascular- may resemble fungi (+ stains) but no budding- no harm except in rare Polyglucosan Body Disease

Subpial corpora amylacea

Astrocytes - Cellular ResponsesInclusions continued...

Rosenthal FibersH&E: Brightly eosinophilic (magenta), hyalinized, elongated, carrot-like, corkscrew, or sausage- like, lumpy-bumpy profiles in astrocytes. Not as orange-red as stacks of erythrocytes.Masson trichrome: Bright red- crystallin3 etiologies: Reactive (chronic conditions) Neoplastic (low-grade, slow growth) Alexander’s disease (mutated GFAP)

Astrocytes - Cellular ResponsesInclusions cont...

Rosenthal fibers cont...

Reactive - typically around cystic lesions (ex. Pineal cyst, craniopharyngioma, vascular malformation)

Neoplastic - characteristic of pilocytic astrocytomas and helpful diagnostically, especially when nuclear pleomorphism is suggestive of a higher grade tumor. Helps greatly in correctly identifying tumors with slow growth. Worthy of big searches.

Astrocytes - Cellular ResponsesInclusions cont...

Eosinophilic Granular Bodies, EGBs

Round, finely granular, pink Also indicative of slow-growing, well- differentiated neoplasms (pilocytic astrocytomas, pleomorphic xanthoastro- cytomas, and gangliogliomasPAS +Variant: protein droplets clustered intracellularly, eosinophilic hyaline globules

Herring bodies in neuro-hypophysis look similar butrepresent stored hormones

Oligodendrocytes (“few branch glia”)

Produce and maintain CNS myelin“Satellite” around neurons in gray matterColumns between bundles of myelinated axons in white matter

H&E: naked, small, dark, uniformly rounded, nuclei - frozen section - no halos - formalin fixed - perinuclear halos (“fried egg” appearance)

ImmunoP: GFAP - S100 +

Oligodendrocytes - Cellular Responses

Loss: leads to demyelination- Multiple sclerosis (MS) plaques

Proliferation: - Edges of active MS plaque - “Myelination gliosis”, normal prolifer- ation of oligodendrocytes during develop- ment in preparation for myelination

Inclusions: - JC virus in PML (enlarged, glassy nuclei due to viral inclusions) - intracytoplasmic inclusion bodies in some degenerative diseases seen with special stains

Astrocytes and Oligodendrocytes

Secondary structures of Scherer - dependent upon interaction of infiltrating tumor cells with normal host tissue elements

Ex. Perineural (perineuronal) satellitosis Surface growth (subpial accumulation) Perivascular satellitosis Others

Ependymal CellsLining of ventricular systemCuboidal, columnar, ciliated epitheliumNo basement membrane, sits on neuropilTanycytes - long processes contact blood vesselsEpendymal granulations are nodular proliferations of astrocytes with focal loss of ependymal lining. Non-specific reaction to injury.Atrophy - flattened, decreased cilia, can be seen in hydrocephaly

Inclusions - herpes, CMVEpendymal cell clusters (developmental rests)

Ependymal CellsNeoplasms - can see 2 types of rosettes

Perivascular, pseudorosette - hallmark - neoplastic ependymal cells surround a blood vessel but leave a nuclear free zone around the vessel filled with cytoplasmic processes (shown below)

“True” ependymal rosette, less common - central well-defined lumen rather than a blood vessel

Blood Vessel

Choroid PlexusSpecialized ependymal cellsLayer of plump, cuboidal/columnar epithelial cells surrounding fibrovascular coresFrond-like projections into ventricles

Secretes CSF (500 ml per day)

S100 +, GFAP -, transthyretin (prealbumin) +Meningothelial whorls and nests - can see calcifications, psammoma bodiesXanthomatous change - foamy cells can form xanthogranulomas

Neoplasms: Choroid plexus papillomas Choroid plexus carcinomas

MicrogliaPrimary immune cells of the CNSDerived from monocytes (CD68+)Antigen presentation, phagocytosis, cytokine secretion, etc.

Resting- oval to elongated nuclei, inconspicuousActivated- very elongated nuclei, “rod cells”Response to CNS injury - diffuse microgliosis or microglial nodules (ex. viral infection)

Resting Activated

Tissue Macrophages of the CNSClosely related to microglia, CD68 +

Gitter cells (“lattice cells”)

Derived from circulating monocytes and indigenous microglia

Spherical cells with well-defined cell borders

Large clusters (easily identified) in destructive processes or scattered cells (can mimic the hypercellularity of gliomas)

Increased mitotic activity &proliferation

MeningesDura (pachymeninx) - dense connective tissueLeptomeninges (pia mater and arachnoid)Arachnoid: - spindled cells under dura - loosely arranged meningothelial cells (EMA+), collagen, fibroblasts, and blood vesselsPia: thin, membrane overlying the brain“Subdural space” - does not really exist, a potential space or path of least resistance for pathologic processes disrupting meningesArachnoid villi - whorled groups of meningo- thelial cells that absorb CSFMay see pigmented melanocytesFibrosis with age

Meninges - Neoplasms

Meningiomas most common Cellular whorls Psammoma bodies Difficult to distinguish cell borders EMA + Desmosomes on electron microscopy

Whorl Psamomma body

Practical Review of Neuropathology, Fuller GN & Goodman, JC, Lippincott, Williams, & Wilkins, Philadelphia, 2001.

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York, 1998.