Case Report: Giant congenital hydronephrosis presenting as massive retroperitoneal cystic lesion with literature review.

Giant retroperitoneal cystic lesions encompass multiple differential diagnoses including renal cysts, lymphangiomas and congenital hydronephrosis. Congenital giant hydronephrosis is extremely rare in adult patients, with limited clinical data to guide preoperative differentiation and surgical management. We report a unique case of a 60-year-old male with a 10-year history of progressive giant left retroperitoneal cystic mass, accompanied by left abdominal distending pain. Preoperative contrast-enhanced ultrasound and CT demonstrated severe left hydronephrosis with markedly atrophic renal cortex. Complete surgical resection of the cystic lesion was performed under laparotomy. Cyst fluid creatinine and postoperative histopathology confirmed the diagnosis of congenital giant hydronephrosis. The patient recovered uneventfully without complications during regular follow-up. We further review published literature to summarize clinical manifestations, multimodal imaging differentiation, surgical indications and long-term prognosis of adult giant congenital hydronephrosis, aiming to provide practical references for clinicians to distinguish retroperitoneal cystic masses and optimize surgical decision-making.