Background: To our knowledge, giant lymph node hyperplasia (Castleman
disease) may present as a pelvic mass on magnetic resonance imaging (M
RI). Case: A postmenopausal woman with rapidly enlarging leiomyoma ute
ri was found to have a suspicious left adnexal mass mimicking an ovari
an neoplasm on preoperative MRI. At laparotomy, the suspected uterus a
nd normal ovaries were extirpated. In addition, a firm, 4 x 8-cm solid
mass within the sigmoid colon mesentery was found and resected. The f
inal 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 di
fficult, despite sophisticated diagnostic imaging studies such as MRI.