A case of retroperitoneal malignant mesenchymoma.

A rare case is reported of malignant mesenchymoma of a retroperitoneal lesion involving the kidney and composed of leiomyosarcoma and liposarcoma. The tumor, measuring 13 x 12 x 11 cm and weighing 1910 g, arising from the soft tissue of the retroperitoneum or renal capsule, was completely removed surgically. Thirteen months after surgical operation, multiple metastasis was observed. Immunohistochemical and electron microscopical examination showed two different mesenchymal elements. Magnetic resonance imaging findings were compatible with the pathological findings. This case appears to be the second in the world literature.