Canine Ependymoma: Diagnostic Criteria and Common Pitfalls

Abstract

Reports of canine ependymoma are generally restricted to single case reports with tumor incidence estimated at 2% to 3% of primary central nervous system (CNS) tumors. While most commonly reported in the lateral ventricle, tumors can occur anywhere in the ventricular system and in extraventricular locations. Rosettes and pseudorosettes are a common histologic feature; however, these features can be mimicked by other CNS neoplasms. Thirty-seven potential ependymoma cases were identified in a retrospective database search of 8 institutions, and a histologic review of all cases was conducted. Of 37 cases, 22 candidate cases were further subjected to a consensus histologic and immunohistochemical review, and only 5 of 37 (13.5%) were conclusively identified as ependymoma. The neuroanatomic locations were the lateral ventricle (3/5), third ventricle (1/5), and mesencephalic aqueduct (1/5). Subtypes were papillary (4/5) and tanycytic (1/5). Histologic features included rosettes (5/5), pseudorosettes (5/5), ependymal canals (2/5), tanycytic differentiation (1/5), blepharoplasts (1/5), ciliated cells (1/5), and high nuclear to cytoplasmic ratio (5/5). Immunolabeling for GFAP (4/4) and CKAE1/3 (3/4) was found in pseudorosettes, rosettes, and scattered individual neoplastic cells. Diffuse but variably intense cytoplasmic S100 immunolabeling was detected in 3 of 4 cases. Olig2 intranuclear immunolabeling was observed in less than 1% of the neoplastic cells (3/3). Tumors that had pseudorosettes and mimicked ependymoma included oligodendroglioma, choroid plexus tumor, pituitary corticotroph adenoma, papillary meningioma, and suprasellar germ cell tumor. These findings indicate that canine ependymoma is an extremely rare neoplasm with histomorphologic features that overlap with other primary CNS neoplasms.

OLIG2 immunolabeling in feline ependymoma

“…6,9 This utility was confirmed in a case series of canine ependymomas in which sparse OLIG2 immunolabeling was recorded in ependymal neoplasms compared to oligodendroglioma, which had robust immunolabeling. 8 This immunolabeling specificity is in direct contrast to our study, in which we found a wide and diverse OLIG2 immunolabeling pattern among feline ependymomas. This immunolabeling pattern appears to be unique among species in which neoplastic ependymal OLIG2 immunolabeling has been studied.…”

“…2,10 OLIG2 immunolabeling is scant in both human and canine ependymoma, with <1% of neoplastic cell immunolabeling in a canine ependymoma study. 7,8 There are no reports of the pattern of OLIG2 immunolabeling in feline ependymoma. Here we describe the clinicopathologic findings and the GFAP and OLIG2 immunolabeling features of 19 cases of feline ependymoma.…”

Canine Primary Intracranial Cancer: A Clinicopathologic and Comparative Review of Glioma, Meningioma, and Choroid Plexus Tumors

“…Histologically, tumors typically form papillary and frond-like arborizing cords and trabeculae supported by a variably dense fibrovascular stroma (Figures 3C–E). Less commonly, areas of more sheet-like growth admixed with pseudorosettes can be found in these tumors (146). Unless invasion into the adjacent parenchyma is present, there are generally few changes in the adjacent tissue and often limited to mild gliosis and edema.…”

High‐grade astrocytoma with ventricular invasion in a dog

“…The immunopositivity for GFAP and Olig2 is highly supportive of a glioma 6 18. Morphological features of canine ependymomas, such as rosettes and pseudorosettes, were not present in the current case; further, although canine ependymomas can express GFAP immunolabelling, Olig2 immunolabelling is rare and scarce 19. Similarly, the papillary fronds typical of choroid plexus tumours were not present in our case,20 and although cytokeratin immunolabelling can occur in choroid plexus tumours, Olig2 is a glial marker that is not expressed by these tumours 9 21.…”