Rhabdomyoma of the orbit.

To our knowledge, this is the first fully documented case of an adult-type orbital rhabdomyoma in an 8-year-old white boy, which originated in the belly of the medial rectus muscle and grew into the anterior orbit to incorporate the trochlea. Incomplete excision resulted in recurrence; the lesion was misinterpreted as a rhabdomyosarcoma and exenteration was performed. The patient was free of disease 25 years later. Reexamination of original pathologic material showed the typical histology of an adult-type rhabdomyoma. Adult-type rhabdomyoma, the most differentiated tumor in a spectrum of benign and malignant striated muscle neoplasms, should be distinguished from fetal rhabdomyoma (also benign) and pleomorphic rhabdomyosarcoma, the malignant striated muscle tumor most likely to be confused with rhabdomyoma. An awareness of the benign nature of rhabdomyoma (rhabdomyoma never evolves into a sarcoma) should prevent unnecessary radical surgery. The tumor can be adequately managed by a local excision that includes all the lobulations of tumor within a margin of normal tissue.