Gastrointestinal stromal tumor metastatic to the orbit

A 53-year-old woman was referred to the authors with a history of left eyelid swelling and retro-orbital pain. She had a history of a prior stomach gastrointestinal stromal tumor (GIST) with metastasis to the liver and intrahepatic bile duct. Examination showed global motility restriction with no relative afferent pupillary defect, and exophthalmometry confirmed 4 mm of left-sided proptosis. Computed tomography imaging showed a heterogeneous mass involving the left inferior rectus muscle with extension to the optic nerve measuring 32.5 mm anterior to posterior and abnormal thickening of the right inferior rectus muscle. An incisional biopsy was performed through a left inferior orbitotomy. Histopathological examination revealed an orbital mass with epithelioid morphology consistent with a metastatic GIST. Immunohistochemical analysis revealed positivity for CD-117 and Dog-1, and negativity for Myogenin. This represents the fifth biopsy-proven GIST metastatic to the orbit in the literature, only the second case with predominantly epithelioid morphology, and only the second case with bilateral orbital metastasis. The authors detail the relevant clinical history, imaging, and pathology.