Ancient Schwannoma of the Female Pelvis Simulating Ovarian Neoplasm: MR Imaging Characteristics and Points of Differential Diagnosis

[Introduction and Purpose] Schwannoma, also referred to as neurilemoma and neurinoma, is a benign nerve sheath tumor which usually occur in the soft tissues of the head and neck and extremities. When the tumors are located in deep structures such as the mediastinum and the retroperitoneum, those tend to be larger masses with degenerative changes as ancient (degenerated) schwannoma. Because schwannomas are usually asymptomatic neurologically, deeply situated tumors are hardly diagnosed in early stage and often become considerably larger with long duration. Ancient schwannomas are encapsulated masses and manifest secondary degenerative changes including cyst formation, calcification and hemorrhage on cut sections. The majority of female pelvic masses arise from reproductive tract, but gastrointestinal, mesenteric, urinary and primary extraperitoneal origin tumors also occur and may mimic gynecologic diseases. Especially masses with cystic nature may closely resemble ovarian neoplasm. Primary extraperitoneal neoplasms are rare and comprise various histologic origins. In the tumors, ancient schwannomas may tend to be mistaken for ovarian disease clinically, because the patients are usually asymptomatic and ultrasonography reveals as cystic masses. Diagnosis before surgical treatment is important for postoperative neurological difficulties often develop. The purpose of this study is to establish the MRI diagnosis of this rare neoplasm.