Idiopathic Retroperitoneal Hematoma.

A 34-year-old female presented with sudden onset of severe abdominal pain in a flank distribution. A large mass was palpable in the right upper quadrant on physical examination. Abdominal contrast-enhanced computed tomography showed a well-defined, right-sided, retroperitoneal cystic lesion located between the abdominal aorta and the inferior vena cava (IVC). The tumor size was 55 × 58 mm, and it compressed the gallbladder and the duodenum. Upper gastrointestinal radiography revealed a stricture of the second portion of the duodenum by the tumor. T2-weighted magnetic resonance imaging showed that the whole part was hyperintense with hypointense rims, but the inner was partially hypointense. Based on the radiological findings, the preoperative differential diagnosis included retroperitoneal teratoma, Schwannoma, abscess, and primary retroperitoneal tumor. On laparotomy, the tumor was located in the right retroperitoneal cavity. Kocher maneuver and medial visceral rotation, which consists of medial reflection of the upper part of right colon and duodenum by incising their lateral peritoneal attachments, were performed. Although a slight adhesion to the IVC was detected, the tumor was removed safely. Thin-section histopathology examination detected neither tumor tissues nor any tissues such as adrenal gland, ovarian tissue, or endometrial implants. The final pathological diagnosis was idiopathic retroperitoneal hematoma; the origin of the bleeding was unclear. The patient was discharged without any complication 5 days after the operation.