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Basic Essentials of
CNS Histopathology
(In Less Than 1 Megabyte)
Marie Beckner, MD
UPMC Neuropathology
March 1, 2002
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Cell Lineage in the CNS
Peripheral blood
Ependymal cells
Microglia
Astrocytes
Oligodendrocytes
O2 A
cells
Neuroepithelial cell in
germinal zone
Neurons
Mesenchymal cells
form blood vessels
& meninges
Overview
Neurons:
Morphology
Stains
Cellular responses
Inclusions
Glia:
Astrocytes
Oligodendrocytes
Ependymal cells
Microglia and macrophages
Meninges
Morphology of neurons, H&E
Projection neurons
Granular cell neurons
Motor neurons
Example of “local
large cell body
circuit” neurons
nucleus with single large
Naked nuclei seen
nucleolus
Lack Nissl substance
prominent basophilic
Nissl substance (RER
& polyribosomes)
axons & dendrites embedded
in surrounding neuropil
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-specific
Others: Chromogranin, PGP9.5, -synuclein,
NeuN, others (growing list)
Neurons: Cellular Responses
Cell body
Chromatolysis
Acute necrosis
Atrophy
Ballooning change
Neuron loss
Neurons: Chromatolytic Changes
Central 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, mesencephalic nucleus of cranial nerve V)
Lipofuscin displacement of nucleus and Nissl
substance
Neurons 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 not
rule 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 (neuronsglia)
- 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 Loss
Final 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 body
ex. Nerve transection, metabolic injury,
and ischemia
CNS - no reinnervation
(2) Retrograde degeneration (distal to proximal)
-“Dying back” process
- Metabolic derangement of entire neuron
- Distal axon most vulnerable
- Usually slow progressive clinical course
ex. “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 catecholamine (dopamine & norepinephrine)
synthesis
- Substantia nigra, locus ceruleus, & dorsal
motor 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), cytomegalovirus (CMV), measles virus (subacute
sclerosing panencephalitis)
“owl’s eye”
large, solitary, clear halo
peripheral 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, noninfectious diseases cont.
(1) Neurofibrillary tangles (NFTs)
- many in Alzheimer’s disease but also
seen in other degenerative conditions, a
few in some older patients, and rarely in a
few other conditions
NFTs assume shape of cell
classically “flame” shape
but may be round, “globoid”
H&E - faint basophilic wisps
Bielschowsky - dark brown,
more prominent
Immunoreactive 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 occasional
rule out Alzheimer’s
disease
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 Tumors
Nissl substance (RER) - Cresyl violet stain
ImP stains (synaptophysin, neurofilament, etc.)
EM (dense - core vesicles, etc.)
Neuronal tumor cell rosettes:
“True” rosette with
central lumen
“Pseudorosette - no
central lumen
Flexner-Wintersteiner rosette
Homer-Wright rosette
(retinoblastomas and PNETs) (Neuroblastoma, Medulloblastoma,
PNETs)
Glia
GFAP S100
Astrocytes (“star” cells)
+
+
Oligodendrocytes
(“few branch glia”)
-
+
Ependymal cells
Tanycytes
Choroid plexus epithelium
+
-
+
+
+
Microglia
-
-
Astrocytes
H & 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)
- bizarre nuclei with atypia that suggests a
malignant astrocytoma
Inclusions
Gliosis continued
Typical - 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 Responses
Inclusions - Age related
Lipofuscin pigment accumulation
Corpora 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 Responses
Inclusions continued...
Rosenthal Fibers
H&E: Brightly eosinophilic (magenta), hyalinized,
elongated, carrot-like, corkscrew, or sausagelike, lumpy-bumpy profiles in astrocytes.
Not as orange-red as stacks of erythrocytes.
Masson trichrome: Bright red
- crystallin
3 etiologies: Reactive (chronic conditions)
Neoplastic (low-grade, slow growth)
Alexander’s disease (mutated GFAP)
Astrocytes - Cellular Responses
Inclusions 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 Responses
Inclusions cont...
Eosinophilic Granular Bodies, EGBs
Round, finely granular, pink
Also indicative of slow-growing, welldifferentiated neoplasms (pilocytic
astrocytomas, pleomorphic xanthoastrocytomas, and gangliogliomas
PAS +
Variant: protein droplets clustered intracellularly,
eosinophilic hyaline globules
Herring bodies in neurohypophysis look similar but
represent stored hormones
Oligodendrocytes (“few branch glia”)
Produce and maintain CNS myelin
“Satellite” around neurons in gray matter
Columns 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 proliferation of oligodendrocytes during development 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 Cells
Lining of ventricular system
Cuboidal, columnar, ciliated epithelium
No basement membrane, sits on neuropil
Tanycytes - long processes contact blood
vessels
Ependymal 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, CMV
Ependymal cell clusters (developmental rests)
Ependymal Cells
Neoplasms - 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 Plexus
Specialized ependymal cells
Layer of plump, cuboidal/columnar epithelial
cells surrounding fibrovascular cores
Frond-like projections into ventricles
Secretes CSF (500 ml per day)
S100 +, GFAP -, transthyretin (prealbumin) +
Meningothelial whorls and nests - can see
calcifications, psammoma bodies
Xanthomatous change - foamy cells can
form xanthogranulomas
Neoplasms: Choroid plexus papillomas
Choroid plexus carcinomas
Microglia
Primary immune cells of the CNS
Derived from monocytes (CD68+)
Antigen presentation, phagocytosis, cytokine
secretion, etc.
Resting- oval to elongated nuclei, inconspicuous
Activated- very elongated nuclei, “rod cells”
Response to CNS injury - diffuse microgliosis
or microglial nodules (ex. viral infection)
Activated
Resting
Tissue Macrophages of the CNS
Closely 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
Meninges
Dura (pachymeninx) - dense connective tissue
Leptomeninges (pia mater and arachnoid)
Arachnoid:
- spindled cells under dura
- loosely arranged meningothelial cells (EMA+),
collagen, fibroblasts, and blood vessels
Pia: thin, membrane overlying the brain
“Subdural space” - does not really exist, a
potential space or path of least resistance for
pathologic processes disrupting meninges
Arachnoid villi - whorled groups of meningothelial cells that absorb CSF
May see pigmented melanocytes
Fibrosis 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.
Neuropathology, Ellison D, Love, S, et al., Mosby, Philadelphia, 1998.
Vinters HV, et al., Diagnositc Neuropathology, Marcel Dekker, New
York, 1998.