Adult rhabdomyoma of the head and neck: a clinicopathologic and immunophenotypic study.

Twenty-seven cases of adult rhabdomyoma (ARM) of the head and neck are reported. The 20 male and seven female patients ranged in age from 33 to 80 years (median age, 60 years). Symptoms included airway obstruction and a mass within the mucosa or soft tissue. Median tumor size was 3.0 cm (range, 1.5 to 7.5 cm). Seven patients (26%) presented with multinodular tumors and one tumor was multicentric. Follow-up was available in 19 cases and ranged from 2 months to 18.5 years after diagnosis (median, 6.0 years). Lesions recurred locally in eight cases (42%) 2 to 11 years after diagnosis (median, 6 years). One recurrence was multicentric. Histologically, ARM was composed of closely packed, large polygonal cells having abundant, eosinophilic, granular, or vacuolated glycogen-rich cytoplasm with focal cross-striations. Immunohistochemical stains confirmed skeletal muscle differentiation; the majority of tumors stained for myoglobin (21 of 21 tumors), muscle-specific actin (21 of 21 tumors), and desmin (19 of 21 tumors). Focal or rare immunoreactivity for vimentin (six of 17 cases), alpha-smooth muscle actin (17 of 20 cases), S-100 protein (14 of 21 cases), and Leu-7 (10 of 20 cases) also was detected. Cytokeratin, epithelial membrane antigen, glial fibrillary acidic protein, and CD68 antigen (with KP1) were not found. The characteristic histology and immunophenotype distinguish ARM from other lesions with which it is frequently confused, including granular cell tumor, hibernoma, oncocytoma, and paraganglioma. The expression of alpha-smooth muscle actin has not been reported previously in ARM; its presence could reflect aberrant expression of smooth muscle actin in skeletal muscle or possibly be a recapitulation of early skeletal muscle embryogenesis.