Hindawi Publishing Corporation Case Reports in Medicine Volume 2010, Article ID 624825, 3 pages doi:10.1155/2010/624825 Case Report Laparoscopic Retrieval of a Peritoneal Mouse Dara O. Kavanagh, Diarmaid Moran, Robert Flynn, and Paul C. Neary Division of Colorectal Surgery, Departments of Colorectal Surgery and Urology, Adelaide and Meath Incorporating the National Children’s Hospital, Tallaght, Dublin 24, Ireland Correspondence should be addressed to Dara O. Kavanagh, dara kav@hotmail.com Received 7 June 2010; Accepted 23 July 2010 Academic Editor: Johann Pfeifer Copyright © 2010 Dara O. Kavanagh et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. A 67-year-old Caucasian male was referred by the urology service with a history of incomplete bowel emptying. He complained of tenesmus. MRI scan suggested a leiomyoma lying anterior to the rectum. He underwent examination under anaesthesia and attempted endorectal ultrasound and biopsy. However, the lesion seemed to migrate cranially and was impalpable. At laparoscopy, a mobile, unattached, 5.5×5×3.5, cream-coloured ‘ egg was retrieved from the retrovesical space. Histology conﬁrmed a hyalinised ﬁbrocollagenous lesion lined with mesothelium. A comprehensive review of the literature is presented. 1. Introduction Peritoneal loose bodies or “peritoneal mice” are asymp- tomatic incidentalomas predominantly found at abdominal surgery or autopsy [1]. They usually are from 0.5 to 2.5 cms in diameter. Giant peritoneal mice (>5 cms) can be associated with symptomatology due to a mass eﬀect. They are thought to evolve from torsion and separation of the appendices epiploicae. Others have suggested that large loose bodies can be formed by the accumulation of peritoneal serum in the appendices epiploicae [2]. Herein, we discuss a giant peritoneal mouse masquerading as a pelvic tumour causing alarming rectal symptoms. 2. Case Report A 67-year-old Caucasian male was referred from the urology service following a previous laparoscopic nephrectomy for clear-cell renal carcinoma. He complained of progressive nar- rowing of his stool with associated symptoms of tenesmus. He was intermittently distended. He denied rectal bleeding or weight loss. His past medical history was unremarkable apart from essential hypertension controlled with an ACE inhibitor. Digital rectal examination was poorly tolerated and subsequent ﬂexible endoscopy suggested an extra rectal lesion encroaching on the posterior wall. Computed tomog- raphy (CT) and magnetic resonance imaging (MRI) showed a smooth-surfaced, well-circumscribed egg-shaped lesion measuring 5.5×5.3×4.4 cms with central calciﬁcations poste- rior to the bladder but anterior and separate from the rectum (Figure 1). Examination under anaesthesia and attempted ultrasound-guided biopsy of this very symptomatic lesion were unsuccessful. The lesion became impalpable and was no longer visible on endorectal ultrasonography. Endoscopy was unremarkable. After the informed consent was obtained, a diagnostic laparoscopy was performed. This revealed a mobile cream-coloured egg anterior to the rectum which was removed via a 4-cm infraumbilical incision (Figure 2). His- tology revealed a mesothelium-lined nodule of extensively hyalinised ﬁbrocollagenous tissue with central calciﬁcation consistent with a “peritoneal loose body”. He made a favourable recovery and was discharged home the following day. He remained symptom-free. 3. Discussion It is generally agreed that peritoneal loose bodies arise from appendices epiploicae. These fat-ﬁlled visceral peri- toneal pouches exist along the antimesenteric taenia of the entire colon [3]. Their physiological signiﬁcance is unclear. When they are subjected to torsion and subsequent infarc- tion, inﬂammatory changes related to peritoneal adhesions, volvulus, bowel obstruction, and perforation may follow.