當「缺失」的腎臟並非真正缺失時：機器人輔助切除巨大囊性發育不良腎，該腎表現類似單側腎發育不全

褚致維、張殷綸

高雄長庚紀念醫院泌尿科

When a “Missing” Kidney Is Not Absent: Robot-Assisted Excision of a Giant Cystic Dysplastic Kidney Mimicking Unilateral Renal Agenesis: A Case Report

Author: Chih-Wei Chu ; Yin-Lun Chang

Department of Urology, Kaohsiung Chang Gung Memorial Hospital and Chang Gung University College of Medicine, Kaohsiung

Introduction: Distinguishing true Unilateral Renal Agenesis (URA) from a completely regressed Multicystic Dysplastic Kidney (MCDK) in adulthood remains a diagnostic challenge. We report a rare case of a giant cystic dysplastic kidney that was preoperatively misdiagnosed as URA and successfully treated using robot-assisted laparoscopic surgery. This case highlights the limitations of cross-sectional imaging and provides insight into the natural progression of MCDK.

Case Presentation: A 47-year-old female presented with intermittent hematuria for 5 years, accompanied by persistent soreness in the right flank. Computed tomography (CT) suggested absence of the right kidney and renal vasculature, along with a 10.3 cm thick-walled cystic mass in the right retroperitoneum containing internal calcifications, raising suspicion for a Bosniak III cyst. The patient underwent a robot-assisted laparoscopic cyst excision. Intraoperatively, meticulous dissection of the cyst wall revealed a distinct tissue area suggestive of an atrophic renal remnant. Further exploration identified a hypoplastic right renal artery, vein, and ureter, all densely embedded within surrounding fibrotic tissue. These structures were resected en bloc with minimal blood loss. Histopathological analysis demonstrated a fibrous cyst wall with thyroidization of renal tubules and the presence of a ureteral remnant. No evidence of malignancy was found, confirming a dysplastic origin.

Discussion and Conclusion: Embryologically, MCDK arises from abnormal ureteric bud–metanephric blastema interaction or early urinary tract obstruction, resulting in dysplastic renal tissue that often involutes over time. In adults, this complete regression can mimic URA on imaging, as residual fibrotic cystic structures obscure underlying renal remnants and hilar anatomy. In this case, histopathological findings—particularly tubular thyroidization—supported chronic dysplasia rather than true agenesis. This highlights the importance of maintaining clinical suspicion for regressed MCDK when evaluating atypical retroperitoneal cystic lesions in patients presumed to have URA. Furthermore, the robot-assisted approach offers enhanced three-dimensional visualization and superior dexterity, facilitating precise identification and safe en bloc excision of aberrant and underdeveloped anatomical structures.