Formerly referred to as granular cell myoblastoma and then as granular cell Schwannoma, this lesion is now referred to as granular cell tumor because of the certainty that it is not myoblastic and the continuing uncertainty of a Schwann cell parentage. It has been described in many viscera, soft tissues, and skin but in most series, the tongue is the most common site. It is found mostly in adults and ordinarily is solitary, but 10% are multiple. Multiple granular cell tumors have been linked to neurofibromatosis. Oral lesions appear as an intramucosal nodule that is painless, pale, and firm. Microscopic examination reveals sheets of tumor cells with abundant, eosinophilic granular cytoplasm and nuclei that show minimal pleomorphism. There is no capsule, and tumor cells extend into surrounding tissues including skeletal muscle where tumor cells may even appear within the sarcolemma. Similarly, nerve trunks may have a halo of tumor cells and they may appear within the nerve sheath. Ultrastructure images show the cytoplasm to be rich in lysosomes that account for the eosinophilic granules and the uptake of the McMannus' Periodic Acid Schiffs stain. Anti S-100 immunoperoxidase stain is positive, lending support to the Schwann cell lineage. Where tumor cells lie near squamous epithelium, it is not unusual to find florid pseudocarcinomatous hyperplasia. It may dominate the field and can easily be mistaken for superficially invasive squamous cell carcinoma. This lesion is treated by surgical excision; recurrences are infrequent. Congenital epulis of the newborn may resemble granular cell tumors histologically but the clinical presentation, negative response to S-100 stain, and the absence of pseudocarcinomatous hyperplasia are distinguishing features.
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