RESUMO
Renal mucinous cystadenoma is very rare with five documented cases in medical literature. Out of these, two developed in horseshoe kidneys. The occurrence of mucinous cystadenoma in horseshoe kidneys is extremely rare and may represent a disorder, wherein such anomalous kidneys may have a tendency to have mucinous tumors taking origin from sequestrated segments of renal pelvic epithelium in the parenchyma. Surgical intervention and thorough histopathologic sampling is required for the diagnosis. It is important to be aware of mucinous cystadenomas while evaluating cystic masses occurring in horseshoe kidney. We report the case of a 52-year old lady who presented with vague abdominal discomfort and on evaluation was found to have a horseshoe kidney with left renal huge cystic lesion with wall enhancement on computerized tomography [CT] scan suggesting malignancy. She underwent left radical nephrectomy with excision of the isthmus. The histological examination revealed a mucinous cystadeno