Metastatic Melanoma Presenting as an Orbital Mass

A 29-year-old male with no past medical history presented with 3 weeks of ptosis and proptosis of the OS. He endorsed OS tearing and strain with eye movements and no diplopia. Visual acuity was 20/20 OD and 20/30 OS. On examination, there was left hyperglobus, reduced OS motility in infraduction, and 3 mm of proptosis (Panel A). MRI of the orbits revealed a heterogeneously enhancing left orbital mass (3.3 × 2.8 × 2.2 cm) extending from the extraconal into the intraconal space with invasion of the inferior rectus muscle and periorbital soft tissues, causing proptosis and globe deformation (Panel B), and a smaller mass in the right lateral orbit above the lateral rectus muscle. Subsequent imaging of the chest, abdomen, and pelvis demonstrated innumerable subcutaneous and pulmonary nodules, bilateral adrenal masses, mediastinal and axillary lymphadenopathy, and osseous lesions, highly suspicious for metastatic disease. The patient underwent orbitotomy with transconjunctival biopsy of the left orbital mass, during which a brown-purple vascular lesion adherent to the inferior rectus muscle was excised (Panel C). Pathology revealed epithelioid and spindle-shaped neoplastic cells with hyperchromatic nuclei, high mitotic activity, a B rapidly accelerated fibrosarcoma proto-oncogene mutation, and positive immunostaining for SOX10, S100, and Melan A, consistent with melanoma (Panel D, hematoxylin and eosin ×20 magnification). He was diagnosed with metastatic melanoma, with bilateral disease in the orbit. Following the orbital biopsy, the primary was discovered on subsequent skin biopsy as malignant melanoma arising in a dysplastic compound nevus on the chest (Panel E). The patient is currently undergoing encorafinib/binimetinib immunotherapy with a good response.