Melanoma, L orbital apex
Findings:
Multiple MR images without and with contrast demonstrate an intermediate signal weakly enhancing mass within the inferior medial left orbital apex. The mass displaces and is inseparable from extraocular muscles. Mild proptosis is evident. Opacification of the left maxillary sinus and ethmoid air cells is likely inflammatory and/or postoperative. A complex mucous retention cyst is incidentally noted in the right sphenoid sinus.
Differential Diagnosis:
Melanoma, metastasis, lymphoma, pseudotumor.
Discussion:
The first three entities above in this location are generally indistinguishable by imaging. While still rare, melanoma is the most common primary ocular malignancy in adults. A focus of extraocular orbital melanoma is more likely to be metastatic than primary. It is not certain in this case whether this is metastatic or primary.