A Case of Malignant Lymphoma with an Elevated Serum IgG4

: A man in his 60s was referred to our hospital for further examination of left hydronephrosis and renal dysfunction. An enhanced abdominal computed tomographic scan showed that the patient had chronic abdominal aortic dissection and a non-enhancing retroperitoneal soft tissue occupying the front of the abdominal aorta as well as the bilateral common iliac arteries. The left ureter was compressed by the soft tissue at the fourth lumbar level. No tumor markers were significantly elevated and idiopathic retroperitoneal fibrosis was suspected to be the cause. Before starting treatment, however, right hydronephrosis was newly observed. We placed bilateral ureteral stents and reviewed our diagnosis. Elevated serum IgG4 and accumulation of 18F-fluorodeoxyglucose in the soft tissue were the points at issue. To determine the diagnosis, we performed open wedge biopsy. Histopathological findings showed mainly fibrous connective tissue with lymphocytic infiltration, which was positive for CD10, CD20, and bcl-2. These findings indicated follicular lymphoma. Induction chemotherapy was performed with 6 cycles of rituximab/cyclophosphamide/vincristine/prednisolone. The soft tissue tumor shrank markedly and the patient has been free from bilateral ureteral stents.