Adult extracardiac rhabdomyoma: light and immunohistochemical studies of two cases in the parapharyngeal space.

BACKGROUND: We present two cases of adult rhabdomyoma in the parapharyngeal space. They are rare benign tumors with a characteristic histologic appearance.

METHODS: The tumors were studied by light and immunohistochemical analysis using stains characteristic of striated muscle fibers.

RESULTS: Cross-striation was demonstrated by phosphotungstic acid hematoxylin (PTAH), muscle specific actin, desmin, and myoglobin while dystrophin was expressed in the cell membranes. Clonal origin was confirmed by expression of myosin heavy chain-fast only. Expression of myosin-neonatal and myogenin proved slight proliferation with incipient differentiation in an otherwise mature tumor.

CONCLUSION: The head and neck area harbors 90% of adult rhabdomyomas and should be considered in a differential diagnosis in this region. Immunohistochemistry confirms that the tumors are almost totally mature neoplasms of clonal origin.