Retroperitoneal ancient schwannoma: two cases and review of literature.

Ancient Schwannomas are rare variants of tumors which arise from the peri-neural Schwann cells. These tumors are termed "ancient" because of the degenerative features acquired with increasing age in these tumors. They are benign, slow growing and usually detected only incidentally or due to local symptoms. Some tumors may demonstrate nuclear atypia, and may be mistakenly termed malignant. Malignant change is usually associated with von Recklinghausen's syndrome in 5% to 18% of cases. Retroperitoneal schwannomas account for only 0.5% to 5% of all cases and are extremely uncommon. They are well encapsulated and recurrences following complete surgical excision are uncommon.