Osseous choristoma of the choroid simulating a choroidal melanoma. Association with a positive 32P test.

We report the clinical and histopathologic features of an osseous choristoma of the choroid that appeared in a 26-year-old woman. Her diagnostic evaluation included a radioactive phosphorus (32P) uptake test, which was 270% positive and led us to believe that the lesion was an atypical malignant melanoma. The extent of true ossification within this tumor, seen microscopically, explains the false-positive uptake of radioactive phosphorus by this benign tumor; it is well known that bone avidly accumulates radioactive phosphorus. We recommend that all "atypical choroidal melanomas" be studied for the presence of bone, with bone-free roentgenograms, ultrasonography, and possibly, computerized tomographic scans before 32P testing or enucleation. This, to our knowledge, is the second histopathologically proved case of an osseous choristoma of the choroid to be reported in the literature.