Rhabdomyoma

Adult rhabdomyoma, the benign neoplasm of striated muscle, is more common in the head and neck region than in any other anatomic site, but it is still a rare neoplasm of the maxillofacial region.  The fetal rhabdomyoma, was first reported on the tongue in 1897 and is considered to be a developmental lesion, not a neoplasm.  It has been reported in persons affected by the basal cell nevus (Gorlin) syndrome.  The term rhabdomyoma is also used to describe a hamartomatous cardiac mass associated with tuberous sclerosis.

The adult form of rhabdomyoma occurs primarily in middle-aged and older individuals, usually (70% of cases) in males.  The most frequent head and neck sites of involvement are the pharynx and the oral cavity, although laryngeal lesions have also been reported.  Within the mouth the oral floor is most often affected, pharyngeal lesions occur most frequently in the base of the tongue and the soft palate.

Fetal rhabdomyoma usually occurs in newborns and young children, but the lesion has been reported in patients as old as 50 years of age.  This type also has a strong male predilection, but cases are usually found within the muscles of the face and the preauricular region, not in the mouth.

Both tumor types present as a nodule or submucosal mass which can become several centimeters in size. Multinodular tumors have been described, with two or more discrete nodules closely adjacent to one another.  Rarely, separate tumors may be found at different anatomic sites.

The adult rhabdomyoma is comprised of an encapsulated mass of large, uniform, polygonal cells with granular eosinophilic cytoplasm. Vacuoles beneath the cell membrane often give the cytoplasm a stellate or "spider web" appearance. With careful observation, cells with cross-striations can be found in almost all cases. A fibrous stroma is present and mitotic activity is extremely low. Many cases demonstrate occasional degeneration vacuoles or clear spaces between the tumor cells.

The fetal rhabdomyoma is comprised of less mature, somewhat pleomorphic, polygonal muscle cells admixed with spindle-shaped cells. This type is typically more cellular than the adult type and often has a myxoid stroma. Mitotic activity is minimal but the more pleomorphic examples can be mistaken for rhabdomyosarcoma.

Cross-striations and crystalline structures are more readily identified with the phospho-tungstic acid-hematoxylin (PTAH) stain, and oil red O staining will often reveal intracellular lipid. Lesional cells are immunoreactive with myoglobin, desmin and alpha-smooth muscle actin.

Both variants of rhabdomyoma are treated by conservative surgical excision.  Recurrence has been reported but is uncommon. Malignant transformation has not been reported.

Corio RL, Lewis DM. Intraoral rhabdomyomas. Oral Surg Oral Med Oral Pathol 1979; 48:525-531.

Kapadia SB, et al. Adult rhabdomyoma of the head and neck: a clinicopathologic and immunophenotypic study. Hum Pathol 1993; 24:608-617.

Box JC, Newman CL, Anastasiades KD, et al. Adult rhabdomyoma -presentation as a cervicomediastinal mass (case-report and review of the literature. Amer Surg 1995; 61:271-276.

Kapadia SB, Meis JM, Frisman DM, Ellis GL, et al. Fetal rhabdomyoma of the head and neck: a clinicopathologic and immunophenotypic study. Hum Pathol 1993; 24:754-765.

Neville BW, McConnel FMS. Multifocal adult rhabdomyoma: report of a case and review of the literature. Arch Otolaryngol 1981. 107:175-178.

Helmberger RC, Stringer SP, Mancuso AA. Rhabdomyoma of the pharyngeal musculature extending into the prestyloid parapharyngeal space. Am J Neuroradiol 1996; 17:1115-1118.

Hardisson D, Jimenezheffernan JA, Nistal M, et al. Neural variant of fetal rhabdomyoma and nevoid basal cell carcinoma syndrome. Histopathol 1996; 29:247-252.