A patient in their mid-60s was referred for evaluation of a
left iris pigmented lesion. The mass had been present for decades and multiple
prior office visits with referring ophthalmologists, most recently 4 years
prior, showed the mass remained stable in size.
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