Uncommon primary pelvic retroperitoneal masses in adults: a pattern-based imaging approach.

There is a broad spectrum of primary pelvic retroperitoneal masses in adults that demonstrate characteristic epidemiologic and histopathologic features and natural histories. These masses may be classified into five distinct subgroups using a pattern-based approach that takes anatomic distribution and certain imaging characteristics into account, allowing greater accuracy in their detection and characterization and helping to optimize patient management. The five groups are cystic (serous and mucinous epithelial neoplasms, pelvic lymphangioma, tailgut cyst, ancient schwannoma), vascular or hypervascular (solitary fibrous tumor, paraganglioma, pelvic arteriovenous malformation, Klippel-Trénaunay-Weber syndrome, extraintestinal GIST [gastrointestinal stromal tumor]), fat-containing (lipoma, liposarcoma, myelolipoma, presacral teratoma), calcified (calcified lymphocele, calcified rejected transplant kidney, rare sarcomas), and myxoid (schwannoma, plexiform neurofibroma, myxoma).Cross-sectional imaging modalities help differentiate the more common gynecologic neoplasms from more unusual masses. In particular, the tissue-specific multiplanar capability of high-resolution magnetic resonance imaging permits better tumor localization and internal characterization, thereby serving as a road map for surgery.