FINAL DIAGNOSIS: RHABDOMYOMA, ADULT TYPE
Rhabdomyomas of the head and neck present as a solitary, slowly growing soft tissue or mucosal mass with symptoms of nasal obstruction, airway obstruction, dysphagia, hoarseness and foreign body sensation. In most cases these tumors are adequately treated by local excision. Recurrences occur in approximately 16% of cases, mainly due to incomplete excision. Due to the slow growth of these tumors, recurrences may occur decades after the initial diagnosis and excision.
Rhabdomyomas are classified by location into cardiac and extracardiac types. The cardiac type is the predominant form of this tumor and is reported to occur in 50% of patients with tuberous sclerosis. This type is thought to be hamartomatous rather than neoplastic. Adult extracardiac rhabdomyomas are extremely rare benign tumors that exhibit mature skeletal muscle differentiation with no known association with tuberous sclerosis. Extracardiac rhabdomyomas demonstrate a predilection for the head and neck region and predominantly affect adult males greater than forty years of age. Both types are histologically similar.
Extracardiac rhabdomyomas are subclassified into adult, fetal and genital histologic variants. The first two show a predilection for the head and neck, but with widely varying age ranges. The adult type generally affects those greater than 40 years of age with a marked male predominance while the fetal type generally affects those under the age of three years. The genital type occurs in the vulvar and vaginal regions of the female genital tract.
Histologically, adult type rhabdomyomas consist of well-demarcated, unencapsulated nodules with densely packed, uniform, polygonal cells containing granular, eosinophilic cytoplasm. The cytoplasm contains occassional large, peripherally located vacuolizations and tends to be rich in glycogen granules with occasional well-oriented cross-striations. The nuclei tend to be small and round, and located both peripherally and centrally. Nuclear pleomorphism, hyperchromatism and mitotic figures are generally absent.
Immunohistochemical stains confirm the skeletal muscle differentiation. Most tumors of this type stain positively for myoglobin, desmin and muscle-specific actin. These tumors may have rare or focal immunoreactivity for vimentin, alpha-smooth muscle actin, Leu-7 (CD57) and S-100 protein stains. Reactivity for cytokeratin, epithelial membrane antigen, glial fibrillary acidic protein and CD68 are generally not found. Immunohistochemical staining helps to distinguish adult type rhabdomyoma from granular cell tumors, hibernomas, oncocytomas and paragangliomas with which they are frequently confused.
Debate as to whether these extracardiac rhabdomyomas are hamartomas, true neoplasms or lesions of disorderly skeletal muscle degeneration and regeneration continues. Recent studies demonstrating clonal cytogenetic abnormalities involving reciprocal translocations of chromosomes 15 and 17, and various abnormalities in chromosome 10 suggest a true neoplastic origin.
Contributed by Gregory P. Fusco, MD, MPH, Mia C. N. Perez, MD and E. Leon Barnes, MD