Progressive enlargement of cavity within melanoma masquerading as iris cyst.

Purpose: To describe progressive enlargement of intralesional cavities within a mass that masqueraded clinically as an iris pigment epithelial cyst for 2 years but later proved to be a melanoma.

Methods: An 81-year-old woman developed asymptomatic focal elevation of the iris, and ultrasound biomicroscopy showed a fluid-filled mass that was interpreted as an iris pigment epithelial cyst. Over a 2-year period of observation, the cavity enlarged from 0.7 to 10 mm, and the solid component enlarged from approximately 6 to 16 mm basal dimension.

Results: On referral, visual acuity was 20/400 in the right eye and 20/25 in the left eye. The affected right eye displayed a pigmented mushroom-shaped ciliary body mass with anterior chamber invasion, distorting the pupil and occupying 40% of the anterior chamber. Ultrasound biomicroscopy and B-scan ultrasonography revealed many cavities within the 14-mm-thick mass, suggestive of ciliary body melanoma. After enucleation, histopathology disclosed multiple cavities, some with granular eosinophilic material, within a mushroom-shaped mixed-cell melanoma.

Conclusion: Cavitation can occur in ciliary body melanoma and can lead to misinterpretation as a cyst. Cavitary melanoma should be considered in the differential diagnosis of cystic lesions of the anterior segment.