What is UPJ obstruction?

The anatomy in plain language

The kidney does not drain straight into the ureter. Urine is first collected by small funnels called calyces, which join into a larger funnel called the renal pelvis. The renal pelvis then narrows into a long thin tube - the ureter - that carries urine down to the bladder. The junction between the renal pelvis and the ureter is the ureteropelvic junction, or UPJ. When that junction is narrow or kinked, urine cannot get out of the kidney as fast as it is being made.

What causes UPJ obstruction?

Most UPJ obstructions are either congenital (present from birth, sometimes only becoming symptomatic in adulthood) or related to a crossing blood vessel. The common patterns are:

• Intrinsic narrowing. A short segment of the UPJ is made of abnormal muscle that does not contract and relax the way the rest of the ureter does. Urine backs up even though the lumen may look open on a static image.
• Crossing vessel. A lower-pole renal artery or vein runs across the UPJ from in front, kinking the ureter whenever the renal pelvis fills. A crossing vessel often explains PUJ pain that is worse after a large drink.
• Post-inflammatory or post-stone scarring. Previous infection, stone surgery, or radiation can scar the junction.
• Rare causes. Fibroepithelial polyps or high insertion of the ureter on the renal pelvis.

Symptoms

UPJ obstruction can present at any age, but in adults the common patterns are:

• Intermittent loin or flank pain, often described as a dull ache with sharper episodes. Pain similar to a kidney stone is common.
• Pain provoked by a high fluid load - coffee, beer, or lots of water - because the kidney makes urine faster than the narrowed UPJ can pass it.
• Nausea that comes on with the pain.
• Recurrent urinary tract infections on one side.
• Blood in the urine (haematuria), sometimes after minor trauma.
• An incidental finding of hydronephrosis on a scan done for another reason.

How it is diagnosed

Imaging confirms both the narrowing and whether it is truly obstructing the kidney.

1. Ultrasound. Useful first screen for hydronephrosis (a dilated renal pelvis). Does not tell you whether the dilation is obstructive.
2. CT urogram (CT IVP). Shows the anatomy of the renal pelvis and ureter, measures the pelvis, and looks for crossing vessels, stones, and tumours.
3. Diuretic MAG3 renogram. A nuclear medicine test that measures split renal function and checks how the affected kidney handles a diuretic. A drainage half-time (T½) longer than about 20 minutes after frusemide is generally considered obstructive.
4. MRI urogram. Sometimes used in younger patients or during pregnancy where radiation is a concern.

What happens if it is not treated?

Some adults with mild UPJ narrowing and only occasional pain can be watched with periodic imaging. Obstruction that causes pain, recurrent infection, stones, or falling kidney function is generally offered surgical repair, because untreated obstruction can progress to permanent loss of kidney function on that side.

How it is treated

The aim of treatment is to widen the UPJ so that urine drains freely. The options are:

• Robotic pyeloplasty - the preferred reconstructive approach for most adults, with long-term success above 95%.
• Laparoscopic pyeloplasty - traditional keyhole reconstruction.
• Open pyeloplasty - for selected anatomies not suited to keyhole surgery.
• Laser endopyelotomy - retrograde endoscopic incision for shorter narrowings, with lower success than reconstruction.