This is a very common, benign choroidal tumor composed of melanocytes. Choroidal nevi are typically incidentally discovered, asymptomatic, pigmented lesions. Up to 15 per cent appear nonpigmented or amelanotic. They are usually composed of spindle-shaped cells with small nuclei, inconspicuous nucleoli and no mitotic figures.
Although the principal challenge for the clinician is to differentiate a choroidal nevus from a malignant melanoma, nonmalignant complications are also possible. When subretinal fluid accumulates at the macular area in the vicinity of a nevus, serous macular detachment can affect vision. Choroidal neovascularization and vitreous hemorrhage are other, rare complications.
This is asymptomatic in the vast majority of cases. Serous macular detachment may present with monocular blurred vision. Photopsias (flashing lights) in the presence of a pigmented choroidal tumor increase the likelihood of malignancy.
Choroidal nevi are variably pigmented lesions. Most are minimally elevated and oval shaped (Fig. 30.1). Small drusen and retinal pigment epithelium (RPE) clumps are often present on the surface (Fig. 30.2). Uncommon complications include serous retinal or macular detachment, choroidal neovascularization and vitreous hemorrhage. Several clinical features have been associated with an increased likelihood of malignancy:
- Continued growth during adulthood
- Tumors larger than three disc diameters wide or more than 2 mm thick (raised)
- The presence of orange (lipofuscin) pigment on the surface of the lesion
- Location of the edge of a lesion within 2 mm of the optic disc
- Serous retinal or macular detachment
- Symptoms (as above).
Most lesions with at least two risk factors probably represent small melanomas; treatment as choroidal melanoma is generally indicated.
Very common (up to 1 in 10 individuals).
The differential diagnosis of choroidal melanoma is potentially life threatening, and must be excluded with caution. Conversely, mistaking a choroidal nevus for a melanoma can result in unnecessary surgery. The yearly rate of transformation from choroidal nevus into malignant melanoma has been estimated at 1 per 10,000.
Melanoma of choroid; melanocytoma of optic nerve; congenital hypertrophy of RPE; combined hamartoma of the retina and RPE.
Choroidal neovascularization; Drusen; Central serous chorioretinopathy; Vitreous hemorrhage.
Ocular tests Ophthalmoscopy is usually sufficient to diagnose a typical choroidal nevus. With fluorescein angiography, small lesions may be undetectable; however, larger lesions are typically hypofluorescent, with small hyperfluorescent areas corresponding to surface drusen. Areas of choroidal neovascularization also stain intensely. Melanomas often contain permeable blood vessels, resulting in a patchy late.
Small slate-grey nevus: these lesions are often slightly paler and less well defined than congenital hypertophy of the retinal pigment epithelium (CHRPE)
Larger nevus with changes to the overlying retinal pigment epithelium and overlying drusen.
phase hyperfluorescence. Unfortunately, however, no known non-invasive investigation can reliably differentiate a choroidal nevus from a small melanoma.
Laser Laser photocoagulation is applied to promote resolution of the subretinal fluid when serous retinal detachment threatens vision.
Review As choroidal nevi are so common, and the probability of malignant change so low, serial examination of all choroidal nevi would be prohibitively expensive. Only lesions with suspicious clinical features require review – initiatly every 3- 6 months, and yearly thereafter. Fundus photography and ultrasonography are often used to monitor growth.
Once growth or other features suggestive of malignancy are detected in an adult, the lesion is treated as a choroidal melanoma.