BACKGROUND: To our knowledge, giant lymph node hyperplasia (Castleman disease) may present as a pelvic mass on magnetic resonance imaging (MRI). CASE: A postmenopausal woman with rapidly enlarging leiomyoma uteri was found to have a suspicious left adnexal mass mimicking an ovarian neoplasm on preoperative MRI. At laparotomy, the suspected uterus and normal ovaries were extirpated. In addition, a firm, 4 x 8-cm solid mass within the sigmoid colon mesentery was found and resected. The final histologic diagnosis was Castleman disease. CONCLUSION: Entities such as Castleman disease should be considered when assessing a pelvic mass. Characterization of the origin of pelvic masses can often be difficult, despite sophisticated diagnostic imaging studies such as MRI.
