[A Case of Retroperitoneal Abscess with Severe Inflammatory Adherence to Inferior Vena Cava]

We report a case of retroperitoneal abscess mimicking a malignant retroperitoneal tumor. A 77-yearold woman was referred to our hospital because of retroperitoneal tumor without any symptoms. The tumor was located just behind the inferior vena cava, and the tumor size was about 38 mm. The tumor showed no abnormal findings in positron emission tomography (PET) and 123I-MIBG scintigraphy. We considered the tumor as benign tumor or retroperitoneal cyst. Follow-up computed tomography (CT) 6 months after the first visit to our department showed no change in the tumor. However, 3months later, she presented with fever, general fatigue and back pain. CT scan at that time showed that the tumor had enlarged to about 70 mm, and the tumor seemed to have invaded into the inferior vena cava. Thrombus into the inferior vena cava was also found. These findings were suggestive of malignancy, so we decided to remove the tumor. During the operation, the tumor was removed together with the inferior vena cava and right kidney because of severe adhesion. The pathological diagnosis was retroperitoneal abscess. Retroperitoneal abscess is caused by various reasons including diabetes mellitus, steroid use, inflammatory disease of gastrointestinal tract and retroperitoneal organs. Although the etiology was unknown in the present case, acute infection of the preexisting retroperitoneal cyst was a possible cause.