Mucinous Cystadenoma of the Kidney: A Rare Case and Literature Review.

Mucinous cystic tumors of the renal pelvis or pyelocaliceal system are extremely rare neoplasms and often mimic complicated renal cysts. Surgical resection is recommended due to the risk of malignant transformation. In September 2023, imaging revealed a cystic lesion measuring 106×93 mm in the right kidney of a 68-year-old male patient, reported as Bosniak type III. The patient underwent right radical nephrectomy. Pathological examination revealed a unilocular cystic lesion lined with mucinous epithelium showing no atypia. Immunohistochemically, epithelial cells were CDX2 positive and PAX8, GATA3, and p63 negative. Findings were consistent with mucinous cystadenoma. No recurrence or metastasis was observed during 18 months of follow-up. The diagnosis of renal mucinous cystadenoma is challenging with preoperative imaging, and the definitive diagnosis is made by postoperative histopathology. Surgical resection and close follow-up are necessary due to the risk of malignant transformation.