11/20/2006 Case 2: Anaplastic glioneuronal tumor

Clinical History:

A 15 year old boy was found to have 4.8 x 3.8 x 4.9 cm cystic, "cortically based", heterogeneously enhancing left temporoparietal lobe mass . A gross total excision was performed.

Diagnostic Notes:

The slides showed a cellular neoplasm which was mostly sharply demarcated from adjacent brain but had some infiltration at a few edges. The tumor had a prominent population of medium size cells with round pale nuclei located at the edge of a brightly eosinophilic cell body, somewhat resembling gemistocytic astrocytes. However the cytoplasm of many of these cells had a distinctly rhabdoid appearance with a round inclusion-like eosinophilic making up most of the cell body. In much of the tumor the cells were rather cohesively packed, almost like oligodendroglioma, but in places they were more discohesive and separate from each other.

The differential diagnosis, both when this was originally worked up and during the discussion of the case, included Atypical Teratoid/Rhabdoid Tumor, Gemistocytic Astrocytoma, and then other less likely possibilities including metastatic carcinoma and melanoma .

Immunostains showed that all of the cells had nuclear immunopositivity for INI-1, thus ruling out an AT/RT. The tumor cells were immunopositive for Vimentin, GFAP, S100, and Neurofilament Protein (RMD020), but not for EMA, Muscle Actin, Desmin, CAM5.2 cytokeratin, synaptophysin, or Neu-N. A MIB1 labeling index was estimated at up to 50%. The diagnosis was thus one of Anaplastic Glioneuronal Tumor.

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