Ureteropelvic Junction Obstruction

Ureteropelvic junction (UPJ) obstruction is a blockage of urine flow from the renal pelvis into the proximal ureter. It causes dilation of the renal pelvis and calyces (hydronephrosis), with progressive risk to renal function.

It is the commonest cause of paediatric hydronephrosis. Incidence is about 1 in 1,000 to 1 in 1,500, with a male predominance of 2 to 3:1 and a left sided preponderance (about 2:1). Bilateral involvement occurs in 10 to 40 percent.

Causes:

• Intrinsic: adynamic segment with abnormal muscle and collagen, ureteric valves, folds or polyps, failure of recanalisation.
• Extrinsic: crossing lower pole vessels in 25 to 50 percent of older children and adults, fibrous bands, kinking.
• Secondary: high grade vesicoureteral reflux with ureteric tortuosity, stones, and postsurgical scarring.

It is associated with multicystic dysplastic kidney on the contralateral side (about 10 percent), contralateral vesicoureteral reflux (10 to 40 percent), and horseshoe kidney or ectopic kidneys.

Adults present with intermittent obstruction and Dietl crisis (episodic flank pain with pelvic distension, typically after a high fluid intake).

• Antenatal hydronephrosis found at the 20-week scan is now the most common presentation; infants are often asymptomatic.
• Palpable abdominal or flank mass in neonates; failure to thrive and feeding difficulty.
• Urinary tract infection and urosepsis, flank pain, and haematuria after minor trauma.
• Older children and adults: intermittent flank pain, often with nausea and vomiting after drinking large fluid volumes (diuresis induced pain), haematuria, and stones.
• Hypertension and rarely renal failure in bilateral disease.
• Examination: flank mass or tenderness; blood pressure may be raised.

• Ultrasound: a dilated renal pelvis with an anteroposterior diameter above 10 mm postnatally (above 15 mm indicates a higher chance of obstruction), calyceal dilation, and a normal ureter and bladder. Assess parenchymal thickness and echogenicity.
• Severity is graded 0 to 4 by the degree of pelvic and calyceal dilation and parenchymal thinning. Repeat postnatal ultrasound after day 3 to 5 (to avoid false negatives from neonatal oliguria), and again at 4 to 6 weeks.
• Diuretic renography (MAG3 with furosemide 1 mg/kg intravenously given 15 minutes before the isotope, F-15 protocol, or at 20 minutes after tracer, F+20). Differential function below 40 percent and a drainage half time (T1/2) above 20 minutes with a plateau or rising curve indicates obstruction. T1/2 below 10 minutes is normal. Perform at 6 weeks of age or older.
• Voiding cystourethrogram to rule out reflux, in the presence of dilated ureters or infection.
• MR urography or CT angiography for adults, to identify crossing vessels and anatomy.
• Urine culture, creatinine, blood pressure.

• Observation: most infants with antenatally detected unilateral hydronephrosis, with differential function above 40 percent and a stable or improving ultrasound, are managed conservatively, since 50 to 70 percent improve or resolve.
• Follow up with ultrasound at 1, 3, 6 and 12 months, then yearly. Repeat renography at 3 to 6 months, then at 1 year if indicated.
• Give continuous antibiotic prophylaxis (trimethoprim 2 mg/kg at night, or amoxicillin 10 mg/kg once daily under 2 months) in high grade hydronephrosis (grade 3 to 4) in the first year, or with dilated ureters.
• Indications for surgery: symptomatic obstruction (pain, recurrent infection, stones), differential function below 40 percent or a drop of more than 10 percent on follow up, worsening hydronephrosis (increasing anteroposterior diameter, parenchymal thinning), a drainage curve showing no improvement, and bilateral severe disease.
• Dismembered pyeloplasty (Anderson-Hynes) is the gold standard, with success above 90 to 95 percent. It excises the obstructed segment and the redundant pelvis, spatulates the ureter and makes a watertight anastomosis with 5-0 or 6-0 absorbable suture. A stent (double-J) or transanastomotic drain is left for 4 to 6 weeks.
• Crossing vessels are transposed (anterior to the repair, the Hellström technique) rather than divided.
• Open flank, laparoscopic or robotic approaches have equivalent results. The laparoscopic/robotic approach is favoured in older children and adults.
• Percutaneous nephrostomy in infection or sepsis or for temporary decompression; antibiotics (ceftriaxone 50 to 75 mg/kg daily, or ampicillin plus gentamicin).
• Endopyelotomy (antegrade or retrograde) is used for secondary or recurrent obstruction in selected adults, with success of 70 to 80 percent. It is not suitable in the presence of crossing vessels or a long stricture.
• Redo pyeloplasty for recurrent obstruction. Nephrectomy for a non-functioning kidney with function below 10 percent and infection or hypertension.
• Follow up: renal ultrasound at 3, 6 and 12 months, and renography at 6 to 12 months post-surgery, with long term yearly monitoring of blood pressure and renal function. Hydronephrosis may take years to improve, and persistent dilation with stable function is acceptable.