Multilocular cystic leiomyoma of the kidney.

A large, multilocular cystic mass from the kidney of a 26-year-old woman was examined by light microscopy and transmission electron microscopy. Ultrastructurally the cysts were shown to be lined by smooth muscle cells, giving evidence that the cysts originated in smooth muscle. Thus the tumor is considered to be a multilocular cystic leiomyoma, an apparently unique renal tumor.