[PRIMARY MALIGNANT LYMPHOMA OF THE RENAL PELVIS : A CASE REPORT].

Primary malignant lymphoma of the renal pelvis is extremely rare ; only 13 cases have been reported to date, and it is often difficult to distinguish from urothelial carcinoma. A 63-year-old woman presented with fever and right flank pain. Computed tomography revealed right hydronephrosis, a renal pelvic mass, and para-aortic lymphadenopathy. Selective urinary cytology was negative, and ureteroscopic examination showed no visible tumor. Because of recurrent febrile urinary tract infections, retroperitoneal laparoscopic right nephrectomy was performed. The resected specimen showed mucosal thickening and a mass lesion in the renal pelvis. Histopathological examination demonstrated diffuse proliferation of atypical lymphoid cells positive for CD20 and CD79a, consistent with diffuse large B-cell lymphoma (DLBCL). The patient received eight cycles of R-THP-COP (rituximab, pirarubicin, cyclophosphamide, vincristine and prednisolone) chemotherapy, and para-aortic lymphadenopathy regressed. She remains in complete remission 60 months after surgery. As imaging findings are nonspecific and urinary cytology is usually negative, preoperative diagnosis of renal pelvic lymphoma is challenging. Nephroureterectomy can serve as both a diagnostic and therapeutic procedure, and malignant lymphoma should be considered in the differential diagnosis of renal pelvic tumors.