Sinonasal rhabdomyosarcoma in children and young adults.

Rhabdomyosarcoma is an aggressive malignant tumor often developing in the head and neck in children. In the sinonasal region, rhabdomyosarcoma constitutes a clinically important group because of the difficulty of surgical resection and its generally poor prognosis. We reviewed the archival pathology materials of 39 cases of rhabdomyosarcoma of the head and neck in children and young adults. The diagnosis was made through light microscopy, immunohistochemistry, electron microscopy, and/or reverse-transcriptase polymerase chain reaction (RT-PCR) molecular testing. We identified 14 tumors in the nose and paranasal sinuses. Patients' ages ranged from 9 to 40 years. Thirteen of the tumors were of the alveolar subtype. In 11 cases, the tumor cells were poorly differentiated, forming a solid alveolar pattern. In 2 cases, there was evidence of rhabdomyoblastic differentiation. Only one case was classified as embryonal rhabdomyosarcoma. A significant number of tumor cells in these cases had clear or vacuolated cytoplasm. Four alveolar rhabdomyosarcoma tumors were tested by RT-PCR; all showed PAX3/FKHR chromosomal translocation. We conclude that sinonasal rhabdomyosarcoma is predominantly of the alveolar subtype and frequently shows clear cells. A review of the literature shows that these tumors carry a poor prognosis, partly because of their parameningeal location and partly because of their "undifferentiated" alveolar histology.