Leiomyoma exhibiting a marked granular change: granular cell leiomyoma versus granular cell schwannoma.

Granular change of leiomyoma or granular cell leiomyoma is rare and not well recognized. It may be confused with the common variety of granular cell tumor, which is currently regarded as being of schwannian origin. A case of granular cell leiomyoma in the periurethral region of a 40-year-old woman is reported. Microscopy indicated that the tumor consisted of polygonal or fusiform cells with coarse, granular eosinophilic cytoplasm. Immunohistochemically, the tumor cells were positive for desmin and actin, but negative for neuron-specific enolase and S-100 protein. Electron microscopy revealed myofilaments in the tumor cells, thus documenting the myogenic origin of the granular cells. The granules were ultrastructurally similar to those of granular cell schwannoma as described in the literature. It is likely that granular cell tumor arises from different tissues.