[A Case of Venous Malformation that Occurred in the Retroperitoneum].

A 70-year-old man complaining of pain in his right leg presented to the Department of Orthopedics in our hospital. X-ray findings revealed calcifications around the left kidney. He was referred to our department for further examination. Computed tomography revealed a tumor 3 cm in diameter with calcifications and an obscure border that was located on the caudal side of the pancreas, anterior to the left iliopsoas muscle and at the left side of the aorta. Magnetic resonance imaging showed that the tumor had comparatively low intensity in diffusion-weighted images and the cell density was not high. The contrast of the tumor by enhanced computed tomography was weak, and we had difficulty judging whether the tumor was benign or malignant. Each tumor marker, immunity factor, and hormone-like catecholamine were within the normal range. We considered the retroperitoneal tumor with calcifications as Castleman disease or tumor of nerve origin. It is believed that most retroperitoneal tumors are malignant. We performed laparoscopic surgery to resect the retroperitoneal tumor. Histopathological diagnosis was a primary retroperitoneal venous malformation. Vascular malformation derived from the retroperitoneum is rare. Furthermore, very few cases of venous malformation in the retroperitoneum have been reported.