JPC SYSTEMIC PATHOLOGY
Signalment (JPC # 1525763): Adult dog; age, breed, and gender unspecified
HISTORY: This dog developed progressive deterioration of the CNS with sudden aggressive behavior.
HISTOPATHOLOGIC DESCRIPTION: Cerebellum and brainstem: Infiltrating the fourth ventricle and adjacent white matter of the brainstem and compressing the adjacent cerebellum, is an unencapsulated, poorly demarcated, densely cellular neoplasm composed of polygonal cells arranged solidly cellular areas supported by a scant fibrovascular stroma. Neoplastic cells have variably distinct cell borders, a scant to moderate amount of eosinophilic, finely-granular to clear cytoplasm, and a prominent perinuclear clear zone (perinuclear halo). Neoplastic cells have one round, hyperchromatic central to paracentral nucleus. There is mild anisocytosis and anisokaryosis. The mitotic rate is less than 1 per 10 HPF. Neoplastic cells are admixed with hemorrhage, edema, fibrin, karyorrhectic and cellular debris. Multifocally at the periphery of the neoplasm, within the brainstem, there is prominent capillary proliferation with occasional formation of glomerular-like tufts.
· Derived from oligodendrocytes; these cells are located in both the white and gray matter
· Purpose of oligodendroglial cells is to myelinate axons and regulate the perineuronal microenvironment
· Occur most commonly in dogs (accounts for 5-12% of all primary nervous system tumors)
· Brachycephalic breed predilection (Boston terriers, boxers, and bulldogs)
· Occur predominantly in adults; 5-11 years of age
· No clear indices of malignancy; all should be regarded as malignant
· Increase in VEGF expression correlates strongly with a high grade tumor
TYPICAL CLINICAL FINDINGS:
· Dogs with oligodendrogliomas are three to four times more likely to have seizures than dogs with other types of primary intracranial neoplasms
· Aggressive behavior, blindness, propulsive gait
TYPICAL GROSS FINDINGS:
· Variably-sized, spherical, well-demarcated neoplasm
· Pink to gray, soft, gelatinous
· Most commonly arises in the frontal, olfactory, temporal or piriform lobes
· All areas of the cerebrum and brainstem, especially in close proximity to the lateral ventricles
o Neoplasm can extend to meningeal and ventricular surfaces
· Occasional multifocal hemorrhage; central area may be cystic in larger tumors
TYPICAL LIGHT MICROSCOPIC FINDINGS:
· Nuclei are remarkably uniform, small, round, hyperchromatic, and centrally to paracentrally located
· Cells have pale or non-staining cytoplasm (perinuclear halo) which imparts a classic fried-egg or honeycomb appearance
· Capillary proliferation that resembles a chicken-wire pattern or glomeruloid vascular tufts at the neoplasm margins
· Densely cellular with little to no stroma, patternless sheets, infrequent mitotic figures, mucinous cystic degeneration, mineralization (+/-), cells often arranged in rows and semi-circles at the periphery of the neoplasm
· Gray matter infiltration with perivascular cuffing and perineuronal neoplastic cell satellitosis
· Anaplastic (malignant) oligodendrogliomas: Large areas of hemorrhage and necrosis, prominent glomeruloid vascular tufts (vasoproliferation), high mitotic rate, nuclear pleomorphism and CSF dissemination of neoplastic cells
· No distinctive features
· Round nucleus, prominent nucleolus, small amount of round and smooth endoplasmic reticulum, abundant free ribosomes, few small mitochondria, vesicles, microtubules, and many short desmosome-like junctions
ADDITIONAL DIAGNOSTIC TESTS:
· MRI, plain radiographs
· CNPase and Olig1/Olig2 positive
· GFAP negative (intermingling astrocytes would be positive)
· Cryptococcosis: Gelatinous appearance (especially in cats)
· Other brain tumors: Primary or metastatic
· Mixed gliomas: Oligoastrocytoma (must contain 25% or more astrocytes); GFAP positive
· Glioblastomas: Differential diagnosis for anaplastic (malignant) oligodendroglioma; blastic astrocytes and oligodendrocytes are GFAP positive; glomeruloid vascular proliferation
· Protoplasmic astrocytoma with cystic degeneration: Small, stellate neoplastic cells separated by clear space
· Extraventricular neurocytoma: Scant eosinophilic cytoplasm with perinuclear halos (similar to the appearance of an oligodendroglioma), fine fibrillary neuropil-like areas resembling the “rosettes” of pineocytomas, ependymoma-like perivascular pseudorosettes
· Rare in cats, cattle, white-tailed deer and horses
· Uncommon in laboratory animals
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