UPJ Obstruction
Pelviureteric junction obstruction blocks drainage from the renal pelvis into the ureter — confirmed by a diuretic renogram, and repaired (pyeloplasty) when symptoms, stones, infection or declining function appear.
The big picture
At the pelviureteric junction, intrinsic narrowing (often congenital) or an external crossing lower-pole vessel impedes drainage. The pelvis dilates while the ureter beyond stays normal calibre — the imaging signature.
Prove obstruction with a renogram, treat for symptoms/stones/infection/function loss, and account for a crossing vessel — pyeloplasty is the gold-standard repair.
Mechanism pathway
Tap any step to see why it happens.
Symptom sorter
The common presentation.
Diagnostic algorithm
Each step answers one question. Tap to expand.
Treatment ladder
Repair obstruction that causes symptoms, stones, infection or function loss; otherwise observe stable, well-functioning systems.
Procedure chooser
- Pyeloplasty (open/laparoscopic/robotic) — the gold standard, transposing a crossing vessel
Complications
- Stones, infection, progressive function loss
- Anastomotic leak/stenosis after pyeloplasty
- Bleeding if a crossing vessel is missed at endopyelotomy
- Identify crossing vessels preoperatively
- Tension-free, well-vascularised anastomosis
- Re-do pyeloplasty for restenosis
- Stent/nephrostomy for leak
Follow-up
- Symptom resolution
- Differential function on renography
- Drainage
- Post-repair renogram to confirm improved drainage
- Relieved obstruction, stable/improved function, no pain
- Persistent obstruction or recurrent stenosis
- Symptoms; surveillance renography
- Restenosis; function loss if untreated
Red flags
Summary tables
UPJ obstruction essentials
| Item | Detail |
|---|---|
| Hallmark | Dilated pelvis, normal-calibre ureter |
| Confirm | Diuretic (MAG3) renogram |
| Pitfall | Lower-pole crossing vessel |
| Gold-standard repair | Pyeloplasty |
Memory hooks
Dilated pelvis + normal ureter = UPJ.
Pain after fluids/alcohol (diuresis).
Prove it with a diuretic renogram.
Crossing vessel → pyeloplasty, not endopyelotomy.
Board traps
Diuresis-related flank pain with a dilated pelvis and normal ureter — UPJ obstruction.
Crossing vessel missed before endopyelotomy.
Well-functioning asymptomatic dilation operated unnecessarily.
Clinical cases
A 24-year-old has recurrent right flank pain after drinking, with a dilated renal pelvis but a normal ureter; CT angiography shows a lower-pole crossing vessel.
What is the diagnosis and the preferred treatment?