Orbital leiomyoma: report of a case and review of the literature.

A 10-year-old female presented with slowly progressive proptosis of 1 year's duration. Orbital MRI revealed an extraconal oval mass occupying the lateral half of the mid and posterior orbit. The tumor was isointense to the extraocular muscle and cerebral gray matter on T1-weighted images and hyperintense on T2-weighted images. The patient underwent superolateral orbitotomy, and it was felt that the tumor was totally excised in a piecemeal fashion. Histopathologic examination showed that the tumor was composed of spindle cells arranged in a fibrous stroma rich in dilated sinusoidal capillaries. The nuclei of tumor cells were oval with blunted ends. There were no mitotic figures. Immunohistochemically, the tumor stained positive with smooth muscle actin, desmin, and vimentin. Based on the histopathologic and immunohistochemical staining results, a diagnosis of orbital leiomyoma was made. At 34 months follow-up, the patient continues to have 20/20 vision and is free of tumor recurrence clinically. Orbital leiomyoma is an uncommon tumor. Search of the English literature showed only 15 previous cases of orbital leiomyoma that have been published since 1963.