Robot-Assisted Anderson–Hynes Pyeloplasty for Lower-Moiety Ureteropelvic Junction Obstruction in an Incomplete Duplex Collecting System Presenting as Dietl’s Crisis: A Case Report

Background/Objectives: Intermittent ureteropelvic junction obstruction (UPJO), classically termed Dietl’s crisis, may be missed when imaging is obtained outside symptomatic periods. The challenge is amplified in duplicated collecting systems, where the obstructed moiety may not be recognized on screening ultrasonography. Case Presentation: A 14-year-old boy presented with recurrent severe right flank pain triggered by heavy fluid intake, associated with nausea and vomiting and separated by symptom-free intervals. An initial renal ultrasound performed between attacks was normal. One week later, the same pain pattern recurred together with a febrile urinary tract infection. Computed tomography urography (CTU) demonstrated an incomplete right duplex collecting system with a bifid ureter, marked hydronephrosis of the lower moiety, delayed contrast excretion, and focal narrowing at the lower-moiety ureteropelvic junction adjacent to one crossing artery and one crossing vein. Diuretic 99mTc-mercaptoacetyltriglycine (MAG3) renography documented obstructive drainage, with a post-furosemide drainage half-time (T1/2) > 20 min, differential renal function of 51% on the right, and split moiety function of 31% (upper) and 20% (lower). The patient underwent transperitoneal robot-assisted dismembered Anderson–Hynes pyeloplasty of the lower moiety with the reconstructed ureteropelvic junction repositioned anterior to the crossing vessels; a 6 Fr × 26 cm double-J stent was placed and subsequently removed at 4 weeks postoperatively. Total skin-to-skin operative time was 75 min, estimated blood loss < 100 mL, and the postoperative course was uneventful. At early 3-month follow-up, the patient remained free of Dietl-type episodes, and ultrasonography showed marked reduction in lower-moiety hydronephrosis. Selective postoperative CTU, obtained because of the unusual bifid anatomy, demonstrated patent drainage. Conclusions: A normal interval ultrasound should not exclude intermittent UPJO when the history is stereotypical, and cross-sectional plus functional imaging is decisive when duplex anatomy and crossing vessels coexist.