Duplicated ureter, UPJ obstruction and posterior urethral valves !

Malformation

Three faults of the tube that carries urine: a double ureter, a narrowing where it leaves the kidney, and folds that block a boy's urethra.

Updated 2026-11-01

See it in 3D: Ureters · Renal pelvis · Kidneys · Urinary bladder · Trigone of bladder · Prostatic urethra

What it is

These three anomalies dilate the urinary tract and are the commonest causes of hydronephrosis found before birth. A duplicated ureter comes from a ureteric bud that splits or from two buds; ureteropelvic junction obstruction is the commonest cause of urinary obstruction in childhood; posterior urethral valves are the main lower obstruction in boys. All three can damage the kidney if not recognized in time.

Embryological cause

Duplication: the ureteric bud splits before entering the blastema (bifid ureter) or two buds sprout from the mesonephric duct (complete duplication).
The bud arising higher on the mesonephric duct drains the upper pole, is absorbed later and opens lower, sometimes outside the bladder.
UPJ obstruction: a segment with disorganized muscle or incomplete recanalization at the pelvis–ureter junction; sometimes a lower-pole vessel compresses it.
Posterior urethral valves: membranous folds in the prostatic urethra; attributed to abnormal integration of the mesonephric ducts into the urethra, though the exact mechanism is unclear.

Markers

Weigert–Meyer

How it presents

Hydronephrosis on prenatal ultrasound, today the commonest way they are found.
Febrile urinary infection in an infant; a palpable abdominal mass in marked cases.
Ureterocele: cystic dilatation of the end of the ureter inside the bladder; it can block the bladder neck.
Valves: weak stream, distended bladder, infection or neonatal renal failure; in severe cases pulmonary hypoplasia from oligohydramnios.
Some boys with valves progress to chronic kidney disease despite treatment.

Diagnosis

Prenatal and postnatal ultrasound: degree of pelvicalyceal dilatation, bladder wall thickness.
Voiding cystourethrogram: diagnoses valves (dilated posterior urethra) and reflux.
Diuretic renal scintigraphy: confirms UPJ obstruction and measures each kidney's function.
MR urography: defines the anatomy of a duplication or ectopic ureter.

Test yourself

Think of the answer, then tap the question to see it.

By the Weigert–Meyer rule, which ureter of a duplex system tends to obstruct?

The one draining the upper pole: it opens lower and more medial, often with a ureterocele or ectopically.

What is the most common cause of congenital hydronephrosis?

Ureteropelvic junction obstruction.

Which clinical finding suggests an ectopic ureter in a girl?

Constant urine dribbling despite normal voiding, because the ureter opens below the sphincter (vagina or vestibule).

Which test confirms posterior urethral valves?

A voiding cystourethrogram, showing the posterior urethra dilated above the valves.

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See it in 3D

The structures of Durgical's 3D anatomy where it is found.

← All of embryology

Educational content on embryonic development; not a guide to prenatal diagnosis or to medicines in pregnancy and no substitute for a health professional's advice. No doses are given.

Sources: Ureteropelvic junction obstruction: MedlinePlus Medical Encyclopedia (MedlinePlus, U.S. National Library of Medicine, 2024); Bilateral hydronephrosis: MedlinePlus Medical Encyclopedia (MedlinePlus, U.S. National Library of Medicine, 2024); Embryology, Kidney, Bladder, and Ureter - StatPearls - NCBI Bookshelf (StatPearls Publishing (NCBI Bookshelf), 2023).

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Representative model, for educational purposes only.