Microscopic description and IHC:

The tissue sections demonstrate a non-infiltrative glial neoplasm showing predominantly fascicular architecture. Unequivocal perivascular rosettes and true rosettes are absent. No necrosis and no microvascular proliferation are present.

The tumor cells are positive for S100 (not shown) and GFAP. EMA shows perinuclear dot like immunoreactivity in tumor cells. Olig2 (not shown) is positive in less than 5% of the cell (a common finding in ependymomas. The Ki67 labeling index is estimated at 4% by manual assessment.

Ultrastructure evaluation demonstrates the tumor cells with abundant intermediate filaments, numerous cell-cell junctions (zonula adherens), and intracellular lumina with abundant microvilli.

The IHC and ultrastructure features unequivocally demonstrate ependymal differentiation of this neoplasm. The fascicular architecture is consistent with the so-call “tanycytic” variant of ependymoma.

Discussion:

Tanycytic ependymona, WHO grade II, is a very rare lesion that shares the same IHC and ultrastructural findings as the conventional ependymoma. It can be easily confused with schwannomas, meningiomas, and fibrillary or pilocytic astrocytomas due to the fasicular/spindled architecture. Studies are limited to case reports and most are seen arising in the intramedullary spine. The word “tanycytic” came from Greek “tanyos”, meaning to stretch.

Electron mircroscope image possibly detecting cancerous areas in human tissue

References:

Rosai, J., & Ackerman, L. V. (2011). Surgical Pathology. Elsevier - Health Sciences Division.

Krisht, Khaled M., and Meic H. Schmidt. "Tanycytic ependymoma: A challenging histological diagnosis." Case reports in neurological medicine2013 (2013).

CASE IMAGES