Description
The melanocytoma is a darkly pigmented benign tumor that usually lies over or adjacent to the optic disc, affecting the choroid and superficial nerve fibre layer. Histologically, it is a variant of a choroidal nevus, composed of polyhedral nevus cells filled with large amounts of densely pigmented cytoplasm. Melanocytoma can also arise in other parts of the uvea, i.e. the iris or ciliary body. Lesions infrequently increase in size, and malignant transformation is rare.
Symptoms
Melanocytoma is usually asymptomatic.
Signs
This is a dark grey- or black-colored benign tumor that usually lies over or adjacent to the optic disc. The appearance on fundoscopy is a densely pigmented, elevated lesion. There are feathery borders related to the infiltration of the nerve fibre layer, in a similar fashion to myelinated nerve fibers. Visual acuity is usually normal. Occasional associated signs include optic disc edema, sheathing of retinal vessels and blind spot enlargement.
Prevalence
Choroidal melanocytoma is rare.
Significance
Choroidal melanocytoma is one of the differential diagnoses of malignant melanoma, a potentially life-threatening condition.
Differential Diagnosis
Melanoma, Choroidal Nevus, Choroidal Haemangioma, Congenital Hypertrophy of the Retinal Pigment Epithelium (CHRPE), Combined Hamartoma of the retina and RPE
Management
Additional investigations
Serial photography will be useful in monitoring for growth or change. Visual field assessment may reveal enlargement of the blind spot or any nerve fibre bundle defect.
If there is doubt about the diagnosis, then ultrasonography may help to confirm the diagnosis and the extent of the tumor. Fluorescein angiography of choroidal melanocytoma will show hypofluorescence due to blockage of the choroidal fluorescence by the pigment cells, whereas a melanoma will typically hyperfluoresce due to the vascularity of the lesion.
Prognosis
Lesions infrequently increase in size, and malignant transformation is considered rare. There are reports of spontaneous necrosis of the lesion, or an association with venous occlusion, with the associated risk of neovascular glaucoma.
Review
In general, treatment is not required. Initial review at 3 month intervals is recommended to detect growth. Yearly review thereafter is sufficient.
Figure 1.
Choroidal melanocytoma overlying the optic disc