Posterior fossa ependymoma

Discussion:

The patient went on to have a resection confirming the diagnosis of an ependymoma. 

Histology

Paraffin sections show a moderately hypercellular tumor. Tumor cells have uniform round and oval nuclei with an open finely granular chromatin pattern and a variable amount of clear and finely granular eosinophilic cytoplasm. These are arranged predominantly in diffuse sheets. Moderately well-formed perivascular pseudo-rosettes are noted and there are cystic and tubular spaces lined by ciliated cells with similar nuclear features to cells within the solid areas. No mitotic figures, vascular or endothelial cell hyperplasia or necrosis are seen. Areas of hyalinisation are noted. Eosinophilic, PAS+ secretory like bodies are seen in the cytoplasm of many tumor cells.

IMMUNOHISTOCHEMISTRY:

  • GFAP positive
  • EMA positive peri-nuclear dot pattern in small number of tumor cells
  • PgR negative
  • CEA negative
  • Topoisomerase labeling index: Approximately 1%

​FINAL DIAGNOSIS: posterior fossa ependymoma (WHO Grade 2).

Note: as molecular profiling was not carried out in this case, it would have the diagnosis of posterior fossa ependymoma not otherwise specified (NOS). 

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