Examqo › Examqo library › Urology › Paediatric urology · IMLE
Ureteropelvic junction obstruction (UPJO)
Obstruction where the renal pelvis meets the ureter is the commonest cause of pathological congenital hydronephrosis; most infant cases improve on their own and are followed, and surgery (pyeloplasty) is done when split function falls, dilatation worsens or there are symptoms.
Why it matters in the exam
In infants the cause is usually an intrinsic segment that does not transmit a peristaltic wave; in older children and adults a vessel crossing the lower pole and pressing on the junction is more common, with intermittent flank pain after heavy drinking (Dietl crisis). Evaluation: ultrasound measuring the anteroposterior pelvic diameter (APD), and a MAG3 scan with furosemide measuring drainage and split function. Guidelines advise doing the ultrasound after day 2 to 3 of life, because in the first days dilatation may look smaller than it is due to relative dehydration.
Indications for surgery: split function below 40 percent, a fall in function of more than 10 percent on follow-up, worsening dilatation, and pain, infections or stones. Slow drainage alone on the scan, when function is preserved, is not an indication for surgery. The standard operation is Anderson-Hynes dismembered pyeloplasty — excision of the narrow segment and a new anastomosis — open, laparoscopic or robotic, with success above 90 percent. Endoscopic incision (endopyelotomy) is less successful and does not suit a crossing vessel.
Hydronephrosis in pregnancy is classified by the UTD system according to pelvic diameter and other findings, and needs ultrasound after birth. When dilatation is bilateral in a boy, or with an abnormal bladder, obstruction below the bladder (PUV) must be considered. Dilatation of the ureter together with the pelvis points to reflux or ureterovesical junction obstruction and not to UPJO. In an adult with newly found UPJO a crossing vessel is sought by CT angiography before surgery.
Key points
- The commonest cause of pathological congenital hydronephrosis.
- MAG3 with furosemide for function and drainage.
- Most infants — follow-up.
- Surgery: below 40 percent, a fall above 10 percent, symptoms.
- Anderson-Hynes — success above 90 percent.
Summary table
| Finding | Meaning | Action |
|---|---|---|
| Dilatation with preserved stable split function | Usually improves | Ultrasound and scan follow-up |
| Split function below 40 percent | Renal damage | Pyeloplasty |
| Fall in function above 10 percent | Worsening | Pyeloplasty |
| Intermittent pain after drinking in an adult | Crossing vessel | Pyeloplasty, not endopyelotomy |
| Ureter dilated with the pelvis | Not UPJO | Evaluate for reflux or lower obstruction |
In the full version for subscribers
- A simple algorithm
- Memory aid
- Exam traps
- 5 review cards
- Enough for IMLE
The full version is open to subscribers of: Urology, Medical licensing exam (IMLE), Pediatrics, Pediatric surgery.
Subscriber? Read the full topic Plans and prices 25 free questions
Sources
- EAU Guidelines on Paediatric Urology, 2025 edition — Dilatation of the upper urinary tract (UPJ and UVJ obstruction)
- Campbell-Walsh-Wein Urology, 12th edition (2020) — Management of Upper Urinary Tract Obstruction
- Society for Fetal Urology and Urinary Tract Dilation consensus classification, 2014 — Prenatal and postnatal grading
Sources are given for further reading; the text is written afresh and not copied from them.
Reviewed by the Examqo AI Professor · 2026-11-06. The text may contain errors; when in doubt, check the source.