Retroperitoneal nerve sheath tumors: an unusual cause of pelvic mass.

Solitary nerve sheath tumors can arise in peripheral, cranial, or sympathetic nerves at virtually any anatomic site. Although origin along the nerves of the retroperitoneal space is not uncommon, these tumors rarely present as pelvic masses. We describe two patients found to have benign nerve sheath tumors of the sacral plexus. Neurilemomas (schwannomas) and neurofibromas are thought to result from a proliferation of perineural cells. These tumors are characteristically firm, smooth, and asymptomatic. They range in size from 1-2 mm to over 20 cm. Surgical excision can usually be accomplished by enucleation of the tumor without damage to the adjacent nerve. Resection of sacral plexus tumors requires knowledge of pelvic retroperitoneal anatomy to avoid injuries to the nearby vascular and urinary structures.