Abstract
RATIONALE: Mucinous adenocarcinoma of the renal pelvis is extremely rare in malignancy of the renal pelvis, and <100 cases have been reported so far. However, horseshoe kidneys appear to be more prone to this mucinous gland metaplasia. Due to the lack of a specific diagnostic basis, it is difficult to confirm the diagnosis before surgery, which is easy to cause misdiagnosis. PATIENT CONCERNS: We report a 64-year-old male patient who found a cystic mass in the left kidney during physical examination. CT examination showed a horseshoe kidney with a cystic mass 9.5 × 8.0 cm in front of the left kidney, lacking obvious diagnostic features. DIAGNOSIS: It was misdiagnosed as cystic teratoma before the operation, and was diagnosed as mucinous adenocarcinoma of the renal pelvis through pathological examination after the operation. INTERVENTIONS: Resection of the tumor by nephron-sparing surgery and postoperative chemotherapy. OUTCOMES: No tumor recurrence was found at 6 years of follow-up. After 7 years, the patient had multiple metastases in the abdominal wall and peritoneum, and no tumor recurrence was found in the urinary system. The patient received chemotherapy again and survived well. LESSONS: The prognosis of nephron-sparing tumor resection for MRAP is not significantly different from that of radical nephroureterectomy + bladder cuff excision. Because it can reduce the risk that patients can not tolerate follow-up chemotherapy due to abnormal renal function after surgery, which may be more beneficial in patients with kidney abnormalities or chronic disease.