UPJ obstruction

Causes

• Congenital - a narrow or muscle-poor segment of the UPJ that has been present since birth, often only symptomatic in adolescence or adult life.
• Crossing vessel - an aberrant lower-pole renal artery that compresses the UPJ from outside.
• Acquired - scar tissue after stone disease, stone surgery, previous pyeloplasty, or trauma.

Symptoms

• Flank or loin pain, often intermittent and worse with high fluid intake (classic "Dietl's crisis").
• Recurrent urinary tract infection of the affected kidney.
• Stones forming in the dilated pelvis.
• Sometimes completely asymptomatic, found when a kidney is imaged for something else.

Diagnosis

• Renal ultrasound - shows hydronephrosis.
• CT urogram or MR urogram - defines the anatomy and looks for a crossing vessel or stones.
• MAG3 diuretic renogram - the key functional test. It quantifies how much of the kidney's function comes from each side, and measures how long urine takes to drain out of the pelvis after a diuretic dose (a prolonged "T½" suggests obstruction).

Treatment

Symptomatic UPJ obstruction, or obstruction with progressive functional loss, is corrected surgically. The standard operation is robotic dismembered pyeloplasty - the narrowed segment is removed and a wide, tension-free anastomosis is fashioned between the pelvis and the spatulated ureter. Long-term patency is consistently above 95% in published series.

When watchful waiting is appropriate

Asymptomatic patients with minor dilatation and good function on renogram can be observed with periodic imaging; intervention is only needed if symptoms develop or function starts to fall.