We report a case of an extremely rare neoplasm, malignant granular cell tumor (MGCT). The tumor occurred in the infratemporal fossa of a 30-year-old man, extended to the left orbital base, into the foramen ovale, and invaded the mandible. A granular cell tumor (GCT) was diagnosed by fine-needle aspiration and core needle biopsy of the mass. The patient underwent a radical subtotal debulking procedure followed by radiotherapy. He is alive with recurrent disease 12 months after presentation. Cytologically, the aspirated material was abundantly cellular showing large polygonal cells with ample granular eosinophilic cytoplasm, eccentric nuclei, and often prominent nucleoli. Histologically, the tumor consisted of solid sheets of similar cells that stained strongly with S-100 protein, neuron-specific enolase (NSE), and vimentin. There was moderate nuclear pleomorphism and broad zones of necrosis. Four mitotic figures per 100 high-power field (HPF) were counted. By electron microscopy, the cytoplasm of the tumor cells was filled with lysosomes. Although, some observers advocate that the diagnosis of a MGCT should be reserved for cases in which lymph node and/or distant organ metastasis is evident, we believe malignancy ought to be considered in any GCT with aggressive clinical course defined by persistent local recurrence and destruction of neighboring structures. Nuclear pleomorphism, necrosis, and presence of any mitotic activity should indicate malignancy.
