SIGNS AND SYMPTOMS
The benign choroidal melanoma, referred to clinically as a choroidal nevus, appears as a flat or slightly elevated slate gray lesion of the posterior fundus. The margins are typically indistinct, and often there are overlying areas of drusen noted within the nevus. In most instances, choroidal nevi remain under two disc diameters (DD) in size, although they may attain sizes of up to 5 DD in some cases.
The malignant choroidal melanoma, in contrast, appears as a mottled, often significantly elevated lesion, ranging in coloration from white to greenish-gray. As it grows, it may break through Bruch's membrane, taking on a mushroom-like appearance. Serous retinal detachments are commonly associated with this presentation. You may also observe overlying orange pigmentation known as lipofuscin. Most malignant melanomas are over 10 DD in size at the time of diagnosis. Most patients with choroidal melanomas are asymptomatic. However, should a significantly large lesion occur in proximity to the macula, the patient may present with metamorphopsia, acuity loss, visual field deficit and/or a hyperopic refractive shift.
A choroidal melanoma represents a focal accumulation of melanocytes at the level of the uvea. In a choroidal nevus, these melanocytes are normal in both form and function. In malignant melanoma, the cells undergo neoplasia, reproducing at a faster rate than usual and resulting in a dysfunctional tumor mass. This tumor is capable of not only local extension but also of distant metastasis. While choroidal nevi do not typically lead to this type of damage, it is believed that they can convert to malignancy; the rate of malignant transformation over a 10-year period is estimated at 21 in 100,000.
Nevi of 2 DD or less are harmless. Document the presentation with photography and, when possible, perform a B-scan and follow-up annually. Nevi between 2 and 5 DD are more suspicious. Either perform or refer for angiography to help differentiate the mass, and follow-up regularly at six-month intervals.
When the lesion is greater than 5 DD, consider it a malignant melanoma until proven otherwise. It may not require immediate treatment if relatively small and demonstrates no growth. But if the presentation suddenly changes dramatically or if sight is threatened, refer to a retinal specialist for treatment.
While a nevus is of little concern, malignant melanoma presents a potentially life-threatening situation because of its propensity toward metastasis. These tumors have been known to spread to the liver, lungs, skin and gastrointestinal tract.
Refer patients with newly detected malignant melanomas to a primary care physician for testing, which may include liver enzymes, carcinoembryonic antigen (CEA), neuroimaging, and chest CT.