Pigmented Iris Lesion: JAMA Ophthalmology Clinical Challenge

The patient's ocular history included cataract extraction with intraocular lens placement and retinal tear of the right eye and cataract of the left eye. Review of systems was negative for any recent changes in health, weight loss, fever, or night sweats.

Visual acuity without correction was 20/20 OD and 20/25+ OS. Intraocular pressures were normal. Slitlamp examination of the right eye was unremarkable, and the left eye had a raised pigmented iris lesion without prominent internal vasculature and with mammillations on the surface (multiple small smooth dome-shaped protuberances on the surface of the tumor). There were large pigment granules on the surface of the tumor and on the adjacent iris surrounding the mass.

There was no ectropion uvea or iris neovascularization. There were mild nuclear sclerotic changes across the lens in the left eye. Ultrasound biomicroscopy showed a homogeneous intrinsic iris solid tumor with a height of 1.4 mm and basal diameter of 4.1 mm, without angle or ciliary body involvement

Patient was diagnosed having Iris melanocytoma and was kept under observation.

Melanocytoma is an intensely pigmented variant of melanocytic nevus, typically juxtapapillary, but rarely in the iris, ciliary body, choroid, or conjunctiva. Iris melanocytomas are darkly pigmented nodular stromal tumors with sharp margins. Typical features include mammillations and stuck-on pigment granules forming seeds on the surface of the tumor, iris, or angle. Generally absent are ectropion uvea, intrinsic vasculature, and sectoral cataract.

Ultrasound biomicroscopy shows an echogenically solid, homogeneous lesion with high internal reflectivity. Diagnostic biopsy is rarely needed for typical-appearing melanocytomas but may be indicated if there is rapid growth or atypical appearance (eg, vasculature, ectropion, cataract). Because of the stability and classic appearance of this patient's melanocytoma, no biopsy was needed. The differential diagnosis includes melanoma, nevus, melanocytoma, and cyst. The solid appearance on ultrasound biomicroscopy excludes cysts. Both melanocytoma and melanoma may demonstrate tumor growth, hyphema, and secondary glaucoma. However, they can be distinguished clinically.

This patient's iris lesion with sharply delineated borders without distortion of adjacent structures is atypical for melanoma. Whereas the absence of growth over many years in this case makes melanoma unlikely, in general, the presence of (slow, gradual) growth does not itself exclude melanocytoma. Treatment of melanomas involves radiotherapy or occasionally iridectomy/iridocyclectomy.

The 2 remaining considerations were a large typical iris nevus (a common diagnosis) or a melanocytoma (a rarer subtype of magnocellular nevus). The large lesion size is atypical for a benign nevus. In contrast, even benign melanocytomas can be quite large and can demonstrate slow growth over time without indicating malignant transformation. On average, 5% of iris melanocytomas will demonstrate growth per year of observation (23% at 5 years and 74% at 15 years). In contrast, only 4.6% of iris nevi grow by 5 years (usually associated with malignant transformation). The presence of mammillations and pigment granule seeds also helps to distinguish the two. For both iris nevus and melanocytoma, the correct management would be observation. Monitoring is required because complications of melanocytoma may include spontaneous necrosis with resultant pigment dispersion causing melanocytomalytic glaucoma and anterior chamber angle invasion, even in the absence of malignant transformation.

The lesion was monitored twice yearly without change. Six years later, the patient was scheduled for routine cataract extraction and requested a concurrent biopsy to confirm the presumptive diagnosis. Biopsy was obtained using a 27-gauge vitrector, which yields a cytology sample and tissue fragments for cell block preparation, which provides a tissue reservoir for immunostaining, if needed. Cytopathology demonstrated mostly round to oval cells filled with large pigment granules and uniformly small nuclei without atypia, consistent with the original presumptive clinical diagnosis of iris melanocytoma. This case demonstrates both the natural history of this entity with appropriate observation management, with fortuitous histologic confirmation after the fact.

Source: Daniel A. Valenzuela, MD; Charles V. Biscotti, MD; Anthony B. Daniels, MD, MSc;JAMA Ophthalmology Clinical Challenge

doi:10.1001/jamaophthalmol.2022.4484