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Orbital Melanoma

Juan E Small, MD - Case Coordinator
Teddy Jinnteh Su, MD - Radiology Discussion
Ron Firestein, MD, PhD - Pathology Discussion
Russell Alan Blinder, MD - Attending Radiologist
Pablo R Ros, MD, MPH - Attending Radiologist

November 24, 2003

Presentation

A 60-year-old woman presented with right eye pain six weeks prior to admission, then developed a rapidly expanding right orbital mass.

Imaging Findings

Computed tomography
Right orbital exenteration specimen
Microscopy

Computed tomography images show a large mass in the medial aspect of the right orbit, causing severe proptosis of the eyeball. The mass enhances avidly following contrast administration. It is not clear whether the mass is displacing or replacing the medial rectus muscle. The tumor appears to extend medially into the nasal cavity.

Differential Diagnosis

The differential diagnosis in this case would focus on neoplastic processes. The most likely possibilities are those arising from bone or muscle of the orbit; it does not appear to arise from the sinus or nasal cavity. Likely diagnoses include pseudotumor, lymphoma, metastasis, and squamous cell carcinoma (although this is less likely). In a patient of this age, a primary sarcoma arising form the muscle is unlikely. The optic nerve appears to be separate and uninvolved. It may also be reasonable to include cutaneous tissue as a possible point of origin.

Diagnosis

Sino-nasal melanoma

Discussion

Pathology Discussion:

The gross specimen is a right orbital exenteration. On the anterior view, the eyelid is swollen and discolored. On the bisected view, the mass is shown to abut the sclera but does not appear to involve the eye itself. It is firm and homogeneously yellow-white. A closer view of the posterior section strengthens the impression that the sclera is not involved.

Microscopy shows sheets of large, pleomorphic cells. There is some involvement of the respiratory epithelium of the sinus, but no involvement of the eye. The densely packed cells are seen to have prominent nucleoli at higher magnification. The cells stained positively for HMB45, MART1, and S100, confirming the diagnosis.

Radiology Discussion:

Destructive orbital lesions can be caused by a number of processes. Infection is the most common, accounting for 60% of primary orbital disease processes; bacterial infections are more common than mycotic infections. Neoplastic processes, however, must also be considered. Possible entities include metastases (in women, breast cancer; in men, lung renal and prostate cancer are the most common), lymphoma, and Wegener’s. In cases of lymphoma, 75% of patients will have systemic lymphoma. This usually affects the anterior portion of the orbit (retrobulbar) and tends to mold around orbital structures, but the malignant lymphomas can destroy bone. Wegener’s mimics inflammatory processes, metastases, and infection, and has a similar CT/MR appearance to pseudotumor and lymphoma. Other, rarer lesions, such as malignant fibrous histiocytoma (erodes bone) and amyloid (may affect paranasal sinuses, bone destruction has been reported) should also be considered.

Orbital melanoma is much less common than uveal melanoma (the uvea consists of the choroid, ciliary body, and iris). In fact, uveal melanoma is actually the most common intraocular tumor of adults (6 per million per year); the incidence of orbital melanoma is not known. There are four types of orbital melanoma: primary, secondary, metastatic, and radiation-induced. Primary orbital melanoma can arise from congenital ocular melanocytosis, congenital blue nevus, and de novo; it is extremely rare. Primary optic nerve melanoma, which can occur due to malignant transformation of an optic disc melanocytoma, is extremely rare but should be considered in the presence of clinical symptoms; the two may be indistinguishable on ophthalmic exam. Secondary orbital melanoma is orbital extension from uveal melanoma, eyelid melanoma, or conjunctival melanoma; this is the most common type. Metastatic orbital melanoma arises from the cutaneous, uveal, or other (unknown) tissues; it is rare and is usually spread hematogenously (there are no lymphatics in the orbit except at the lacrimal gland regions). Radiation-induced orbital melanoma has been known to develop in the ipsilateral eye after radiation for rhabdomyosarcoma, but is so rare that the relationship is not completely clear. Regardless of the type, orbital melanoma typically presents with proptosis (with or without pain). CT and MRI usually show a well circumscribed, enhancing orbital mass. In some cases, however, the lesion may be diffuse and poorly circumscribed. Treatment is variable depending on the lesion: observation, local resection, radiotherapy, or orbital exenteration may be recommended.

References

Curtin HD, Som PM, editors. Head and Neck Imaging, 4th ed. 2003. Chapter 8, 9

Mafee MF. Uveal Melanoma, Choroidal Hemangioma, and Simulating Lesions, Radiologic Clinics of North America 1998. 36(6); 1083-1099

Shields JA, Shields CL. Orbital Malignant Melanoma: The 2002 Sean B. Murphy Lecture. Ophthalmic Plastic and Reconstructive Surgery 2003. 19(4); 262-269

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