Ellipsoid Smooth Muscle Tumor of the Lower Eyelid: An Exploration of Its Possible Origin.

Ocular adnexal smooth muscle masses/neoplasms are extremely rare. Such lesions are comparatively more common in the conjunctiva than in the orbit and are most unusual in the eyelid. A 58-year-old woman slowly developed over 4 months a firm, movable sausage-shaped lesion in the deep lateral half of the right lower eyelid. The lesion ran parallel to and above the orbital rim. At surgery, the lesion was located between the orbicularis muscle and the inferior orbital septum. The term ellipsoid is used descriptively and does not imply any particular biologic behavior. Immunohistochemical evaluation revealed smooth muscle actin and desmin positivity. Due to the ubiquity of small blood vessels and the absence of smooth muscle bundles in the potential space between the orbicularis striated muscle and the inferior orbital septum, venular smooth muscle emerges as a highly likely source for the lesion.