Melanotic peritoneal cyst. Light-microscopic and ultrastructural studies.

We describe a patient with a melanotic peritoneal cyst. The multilocular cyst was lined by heavily pigmented mesothelial cells. Scattered dendritic melanocytes were also seen underlying the mesothelium. By light and electron microscopy, the lesion appeared to imitate the pigmentation process of the skin. Special stains, to confirm the character of both mesothelial and dendritic cells (melanocytes), were also performed. The above findings constitute the first complete documentation of the relationship of melanocytes with mesothelial cells in humans. Thus, the possibility of primary melanosis peritonei, independent of melanogenic tumors of the ovary, is shown.