Abstract

Clear cell sarcoma of tendons and aponeuroses is the term coined by Enzinger in 1965 to describe a rare but unique type of soft tisse neoplasm whose cells characteristically have the capacity to produce melanin. The authors experienced a case of 64-year old female who presented with a 6x5x4 cm sized mass deeply seated in the left popliteal fossa. The mass was firm and multinodular, and on cut section revealed patches of brown black pigmentation. Histologically the tumor was composed of round to fusiform cells with clear or pale eosinophilic cytoplasm that contained small amounts of glycogen, separated into compact nests or short fascicles by delicate septa of fibrous tissue. The brown black pigment seen in tumor cells and stroma was proven to be melanin by special stain, and ultrastructural examination showed melanosomes in varying stages of development dispersed freely in the cytoplasm or in the lysosomes. These findings strongly support the view that clear cell sarcoma is a tumor of neural crest origin rather than of tenosynovial mesenchyme origin, and is a soft tissue variant of malignant melanoma.