Developmentally heterotopic urogenital tissues in a retroperitoneal lipoma with hematopoiesis.

This report concerns an unusual retroperitoneal lipoma with hematopoiesis in a 49-year-old male. A unique feature is the presence of well differentiated male urogenital tissues, such as the prostatic gland, urethra and urinary bladder in part of the tumor. The process of the differentiation of these tissues is also illustrated. Although this lipoma attained a large size weighing 1,500 g, it is apparently a kind of malformation derived from the sequestered retroperitoneal Wolffian vestige. No similar cases have so far been reported in the world literature.