Double primary carcinoid tumors of the kidney

Abstract Primary renal carcinoid tumor is extremely rare. Because of its similar presentation with other renal tumors, 14.5% were initially misdiagnosed. A 37-year-old female was referred to our department due to incidentally finding of left kidney tumor by sonography. She didn't present flank pain or gross hematuria, also absence of positive physical findings. The patient's general blood routine, urine routine, and renal function examination were all within normal limits. Abdomen computed tomography showed two soft tissue mass within left kidney. The larger renal tumor was about 3.8 cm in size, mild contrast enhancement and small cystic foci abutting renal sinus. The smaller renal mass was exophytic with same image characteristics. The subsequent kidney magnetic resonance imaging reported two lesions had persistent high diffusion-weighted imaging signal intensity, which strongly favor solid neoplasm. Differential diagnosis included renal cell carcinioma, benign adenoma and Wilm's tumor. Hence, frozen section of the smaller renal nodule was sent for pathologist, and it reported no evidence of obvious malignancy. We later performed open partial nephrectomy. The final pathology reported two well-differentiated grade 1 neuroendocrine (carcinoid) tumors. Immunohistochemistry showed these two lesions were strong positive for synaptophysin and neuron-specific enolase (NSE), but negative for WT-1 and vimentin, which were consistent with features of neuroendocrine tumor. Two weeks after operation, patient's serum creatinine was within normal limits. Abdomen computed tomography reported no specific lymph node involvement after 6 months. Primary renal carcinoid tumors are usually found incidentally, and nephron-sparing surgery whenever possible remains the standard treatment of choice.