DIFFERENTIAL DIAGNOSIS OF UVEAL MELANOMA

Peter Reed Pavan (Tampa)

No one feature of uveal melanoma is diagnostic. However, by integrating information from the history, physical examination, fluorescein angiography, and ultrasonography, a greater than 99.7 % accuracy was achieved in the Collaborative Ocular Melanoma Study. Uveal melanomas are typically dome shaped, solitary, and darkly pigmented, sometimes with orange pigment on the surface. They are hyper-fluorescent on fluorescein angiography. Ultrasonograpy shows a solid lesion with low internal reflectivity and, in some instances, vascular pulsations. Malignant melanoma is typically slow growing until it breaks through Bruch's membrane. Then it assumes a characteristic mushroom shape and can expand fairly rapidly. Non-pigmented melanomas are not uncommon.

Malignant melanomas must be differentiated from a variety of lesions including nevus, retinal pigment epithelial hypertrophy, choroidal hemangioma, choroidal osteoma, and choroidal hemorrhage. Differentiating features of these lesions from uveal melanoma are as follows: Nevi are hypofluorescent and have high internal reflectivity. Retinal pigment epithelial hypertrophy has a sharper edge, is minimally elevated, and may have sharply bordered nonpigmented areas within it called lacunae. Choroidal hemangioma has an orange-red color and high internal reflectivity. Choroidal osteoma is highly reflective with dense shadowing posterior to it on ultrasonography. Choroidal hemorrhage is hypofluorescent and will totally or partially resorb over a few weeks.

Disciform lesions and retinal pigment epithelial detachments must be differentiated from non-pigmented melanomas. A small pigmented nevus on the edge of an elevated non-pigmented lesion is highly suggestive of a malignant melanoma. Disciform lesions may have a history of arising from a choroidal neovascular membrane. Disciform lesions and retinal pigment epithelial detachments are often associated with other signs of age-related macular degeneration such as drusen in the same or fellow eye.

Choroidal metastases are often multilobular, multifocal, and sometimes bilateral. They tend to be broader and lower than malignant melanomas and commonly appear yellow with pigmented "leopard" spots on their surface. Reflectivity is moderate to high. Growth can be moderately rapid. A history of a primary cancer elsewhere or the finding of cancer elsewhere supports the diagnosis of choroidal metastases.

In summary, the vast majority of lesions can be differentiated from uveal melanoma. However, 100 % diagnostic accuracy is not achievable. It is wise to document that the patient was informed he may have a benign lesion before enucleation.


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