Orbital leiomyoma: histopathologic and immunohistochemical findings of a rare tumor.

A 51-year-old man was referred for evaluation of a right orbital hemangioma. Ophthalmologic examination was unremarkable except for 1 mm of proptosis OD. CT revealed a 10-mm lesion with evidence of growth from 6 to 10 mm within a year. The tumor did not compromise other orbital structures. An excisional biopsy was performed. On the basis of the histopathologic and immunohistochemical findings, the diagnosis of orbital leiomyoma was established. Orbital leiomyoma is a slow-growing tumor that can be located anywhere in the orbit. Posterior tumors are believed to originate from smooth muscle cells of vessel walls; anterior lesions may arise from the capsulopalpebral or Müller muscle. Although there are no unique features that help the radiologist to exclude other benign lesions of the orbit, the histopathologic diagnosis using immunohistochemical markers is usually straightforward. Attention to the cytologic features that exclude the malignant variant is of utmost relevance for proper diagnosis and patient counseling.