Posterior fossa ependymoma

There is a solid frond-like mass occupying and expanding the inferior aspect of the fourth ventricle, with the tumor extending through the right foramen of Luschka and inferiorly through the foramen of Magendie and causing mild hydrocephalus. The caudal extent of the tumor reaches the level of C1-C2. This tumor has low T1 signal and increased T2/FLAIR signal, with heterogeneous though not intense contrast enhancement, and multiple small susceptibility foci consistent with microhemorrhages. It does not cause restricted diffusion compared to the brain parenchyma. There is a mass effect with anterior displacement of the medulla oblongata on the right. Associated cerebellar descent below the foramen magnum. The remainder of the brain appears normal, there is no transependymal edema surrounding the hydrocephalus. No evidence of leptomeningeal/CSF seeding within the brain or imaged upper cervical spine.

Sections show a moderately cellular tumor with a fibrillary background forming prominent perivascular pseudorosettes and focal ependymal canals. No true ependymal rosettes are seen. Tumor cells demonstrate mildly enlarged elongated nuclei and small nucleoli. No mitoses, necrosis or microvascular proliferation are seen. Immunohistochemically tumor cells stain:

• GFAP positive
• ATRX positive
• IDH1 negative
• p53 negative
• EMA negative
• Ki67 proliferation index is approximately 5%.

FINAL DIAGNOSIS: posterior fossa ependymoma (WHO Grade 2)

Slide images courtesy of the RMH Pathology Department.