Malignant lymphoma of mucosa-associated lymphoid tissue involving the renal pelvis and the entire ureter: A case report.

Mucosa-associated lymphoid tissue (MALT) lymphoma occurs in various sites, but rarely in the urinary tract. Imaging studies of a 69-year-old male revealed a left hydronephrosis and diffuse thickening of the renal pelvic and upper ureteral wall. Retrograde pyelography revealed a narrowing in this region, and brush cytology specimens contained atypical cells. As the lesion was considered to be malignant, surgical excision was performed. Histological analysis revealed an intense lymphoid infiltrate mainly consisting of B cells. The immunohistochemistry results demonstrated that the lesion was positive for CD20 and CD79a and negative for CD5 and cyclin D1. These findings led to a diagnosis of MALT lymphoma. Pathological exploration disclosed a focally dense invasion of lymphoma cells into not only the renal pelvis, but the whole ureteral wall and surrounding tissue; therefore, the patient underwent eight courses of rituximab treatment. Diffuse invasion of lymphoma cells into the whole ureter was rarely observed. Since the surgery, the patient has survived for 78 months without evidence of a recurrence of lymphoma.