Heterotopic brain tissue in the orbit.
A 3-month-old female infant with Turner's syndrome was noted to have progressive swelling of the left upper lid at the age of 1 month. A computed tomogram demonstrated a well-circumscribed, low-density, homogeneous orbital mass. Initially, the main clinical differential diagnosis included dermoid cyst, hemangioma, and encephalocele. Medial orbitotomy followed by histopathologic examination disclosed a cystic choristomatous malformation containing brain tissue. No choroid plexuses within the mass were demonstrated on microscopic examination. Aspiration of fluid from the cystic mass and subsequent biochemical studies unequivocally demonstrated that the mass was filled with cerebrospinal fluid. Despite five surgical procedures, including two frontal craniotomies, and specialized roentgenographic studies, no communication could be demonstrated between the orbital mass and the central nervous system. We postulate that the cerebrospinal fluid was produced within the orbital mass, which represented ectopic brain tissue. Problems in diagnosis and management of this unusual orbital malformation are discussed.