Melanocytic Tumors: Malignant Melanoma
The most common primary intraocular malignancy in adults is uveal malignant melanoma. The tumor can arise from the choroid, ciliary body or iris(1). The tumor may consist of spindle A cells, spindle B cells or epithelioid cells. Mixed cell tumors consist of spindle cells with at least 5-10% epithelioid cells. The cells type helps predict the metastatic potential. Spindle cell tumors have a much lower incidence of spread in comparison to epithelioid cell tumors. Mixed cells tumors behave in between the spindle and epithelioid cell tumors. Other factors associated with predicting metastasis are location(iris tumors have a lower incidence of metastasis than choroidal or ciliary body tumors), size of the tumor in contact with the sclera, and if evidence of scleral invasion.
The tumor may be pigmented or amelanotic. Usually the tumor grows into a discrete lesion, however it can grow in a diffuse fashion which is difficult to detect early on. As a choroidal melanoma tumor grows, it exerts pressure on Bruch's membrane, eventually rupturing it. The tumor then demonstrates a mushroom-shaped configuration. Usually a serous retinal detachment is associated with the tumor at this time. Tumors can gain access to the orbit through emissary veins. However the most common spread is through the blood to the liver. Melanomas of the uvea have a high incidence of liver metastasis. When melanoma is suspected, a complete work-up for metastatic disease is indicated. Liver function tests and periodic physical examinations are recommended after a diagnosis of melanoma is made.
On ultrasonography (1), melanoma of the uveal tract have a distinct signal of low reflectivity due to the sheets of fairly uniform cells. Transillumination can detail the extent of ciliary body tumors showing a transilluminatiion defect in the area of the tumor. Back to Main