A granular cell tumor of the floor of the mouth

Immunohistochemical and electron microscopical observations

Abstract

The granular cell tumor is a rare lesion with a predilection for the subcutaneous region and the tongue, it's histogenesis is still controversial. A 59 year-old female presented with a granular cell tumor in the left floor of the mouth.
The tumor was excised together with a part of the sublingual gland, but invasion of the Wharton's duct was not observed. In the excised specimen, there was no encapsulation and the tumor had partially invaded the sublingual gland. Beneath the overlying stratified squamous epithelium associated with pseudo-epitheliomatous hyperplasia, the tumor cells had proliferated diffusely and/or were arranged in small nests especially around the peripheral nerve bundles. Scattered axon like dark brown fibrils were seen in the tumor nests after Bodian silver staining. The intracytoplasmic granules of the tumor cell showed either a weak or sometimes a strong PAS positive reaction which was diastase resistant. The tumor cells and Schwann cells were positive when tested by the immunohistochemical method using anti S-100 protein antiserum. Electron microscopical observation revealed granules of various sizes and shapes bounded by a membrane in the cytoplasm of the tumor cell. The tumor nest, which was bounded by a basement membrane, consisted of tightly packed spindle shaped cells with long pseudopodial-like processes. Isolated tumor cells were also found within the basement membrane of peripheral unmyelinated nerve fibers adjacent to Schwann cells and axons.
These findings suggest that histogenesis in this case is from Schwann cells of the peripheral unmyelinated nerve fibers.