Granular Cell Tumor of the Neurohypophysis With TFE-3 Expression: A Rare Case Report

Granular cell tumor (GCT) rarely involves the central nervous system, and fewer than 100 cases have been reported in English literatures. We herein report a case of a 36-year-old Chinese man with GCT of the neurohypophysis. Magnetic resonance imaging showed one mass located in the hypophysis with heterogeneous contrast enhancement. Pathological examination showed a neoplasm comprising densely packed polygonal cells of ample cytoplasm with abundant eosinophilic granules inside. The nuclei were small with inconspicuous nucleoli and yet without any mitoses. The tumor was positive for S-100, CD68, CD163, lysosome, and vimentin. Translocation factor E-3 (TFE-3) was diffusely nuclear positive although ASPSCR1-TFE-3 fusion was not detected by fluorescence in situ hybridization. GCT of the neurohypophysis is supposed to be considered under differential diagnosis with neoplasms or lesions of histiocytic origin and others such as pituitocytoma and spindle cell oncocytoma. A group of markers such as GFAP, EMA, CD68, S-100, and PAS staining are useful in complementary diagnosis and TFE-3 may be an alternative marker.