Objectives Castleman´s disease is an extremely rare benign lymphoproliferative disorder usually presenting in the mediastinum, abdomen or neck and less common located at axilla, pelvis and pancreas. Commonly asymptomatic, patients are presented with a large mass noted on physical examination or imaging studies and are often misdiagnosed as an adnexal mass. There are only few cases of pelvic Castleman´s disease reported in the literature. We present a case of Castleman´s disease located in the pelvic cavity specifically in the retropubic space.

Methods A 56 year-old asymptomatic woman was referred to our service with a 5cm-sized pelvic mass detected during a Computed Tomography Scan. Pelvic ultrasound reported an anechoic rounded 5x4x4cm-sized mass with increased flow around the lesion and significant posterior acoustic enhancement.

Results Exploration of the pelvic cavity revealed a circumscribed and well-delineated 8cm-sized mass located in the space of Retzius with dense fibrous adhesions and rich periphery vascularity. Microscopic examination demonstrated large follicles dispersed in a mass of lymphoid tissue. Follicles show marked vascular proliferation and hyalinization of their abnormal germinal centers with a concentric layer of lymphocytes on the periphery of the follicles, which gives an appearance of onion skin. Patient recovered without complications. Five months after surgery no signs of recurrence are reported.

Conclusions Castleman´s disease is a very rare lymphoproliferative condition.Complete surgical resection has good prognosis and a low rate of relapse. Despite the low incidence of this disease must be consider as a differential diagnosis of pelvic mass so we can offer our patient a correct treatment and surveillance.