[Durgical](https://durgical.com/en/) › [DurgiPedia](https://durgical.com/en/durgipedia/) › [Embryology](https://durgical.com/en/embryology/) › [Urogenital system](https://durgical.com/en/embryology/#a-urogenital) › Duplicated ureter, UPJ obstruction and posterior urethral valves [Embryology](https://durgical.com/en/embryology/) · [Urogenital system](https://durgical.com/en/embryology/#a-urogenital) # 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](https://durgical.com/en/anatomy/ureter/) · [Renal pelvis](https://durgical.com/en/anatomy/renal-pelvis/) · [Kidneys](https://durgical.com/en/anatomy/kidney/) · [Urinary bladder](https://durgical.com/en/anatomy/urinary-bladder/) · [Trigone of bladder](https://durgical.com/en/anatomy/trigone-of-bladder/) · [Prostatic urethra](https://durgical.com/en/anatomy/prostatic-urethra-seminal-colliculus/) ## Key points - Complete duplication: two ureteric buds; partial (bifid ureter): one bud that splits early. - Weigert–Meyer rule: the upper-pole ureter opens lower and more medial and tends to obstruct (ureterocele); the lower-pole ureter opens higher and more lateral and tends to reflux. - Ectopic ureter in a girl (below the sphincter, into vagina or vestibule): constant dribbling with normal voiding. - Ureteropelvic junction obstruction: the commonest cause of congenital hydronephrosis; a narrow segment or a crossing vessel. - Posterior urethral valves: males only; thick bladder, bilateral hydroureteronephrosis and oligohydramnios. - “Keyhole” sign on ultrasound: distended bladder with a dilated posterior 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. ## Memory aid “Upper blocks, lower backs up”: upper pole obstructed, lower pole refluxing. ## 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. [Add to my cards (4)](https://durgical.app/estudiar/?add=/en/embryology/duplicated-ureter-upj-obstruction-and-posterior-urethral-valves/) ## See it in 3D The structures of Durgical's 3D anatomy where it is found. - [Ureters](https://durgical.com/en/anatomy/ureter/) - [Renal pelvis](https://durgical.com/en/anatomy/renal-pelvis/) - [Kidneys](https://durgical.com/en/anatomy/kidney/) - [Urinary bladder](https://durgical.com/en/anatomy/urinary-bladder/) - [Trigone of bladder](https://durgical.com/en/anatomy/trigone-of-bladder/) - [Prostatic urethra](https://durgical.com/en/anatomy/prostatic-urethra-seminal-colliculus/) ## Related - [Kidney: pronephros, mesonephros, metanephros and ascent](https://durgical.com/en/embryology/kidney-pronephros-mesonephros-metanephros-and-ascent/) - [Bladder, urachus and urethra](https://durgical.com/en/embryology/bladder-urachus-and-urethra/) - [Horseshoe kidney and renal ectopia](https://durgical.com/en/embryology/horseshoe-kidney-and-renal-ectopia/) - [Multicystic dysplastic kidney and polycystic kidney disease](https://durgical.com/en/embryology/multicystic-dysplastic-kidney-and-polycystic-kidney-disease/) - [Urachal anomalies: patent urachus, cyst and sinus](https://durgical.com/en/embryology/urachal-anomalies-patent-urachus-cyst-and-sinus/) - [Amniotic fluid: polyhydramnios and oligohydramnios](https://durgical.com/en/embryology/amniotic-fluid-polyhydramnios-and-oligohydramnios/) - [Pulmonary hypoplasia](https://durgical.com/en/embryology/pulmonary-hypoplasia/) - [Poland sequence and prune belly syndrome](https://durgical.com/en/embryology/poland-sequence-and-prune-belly-syndrome/) ## Related conditions - [Vesicoureteral reflux](https://durgical.com/en/conditions/vesicoureteral-reflux/) - [Urinary tract infection (acute cystitis)](https://durgical.com/en/conditions/urinary-tract-infection/) - [Chronic kidney disease](https://durgical.com/en/conditions/chronic-kidney-disease/) [← All of embryology](https://durgical.com/en/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](https://www.medlineplus.gov/ency/article/001267.htm) (MedlinePlus, U.S. National Library of Medicine, 2024); [Bilateral hydronephrosis: MedlinePlus Medical Encyclopedia](https://medlineplus.gov/ency/article/000474.htm) (MedlinePlus, U.S. National Library of Medicine, 2024); [Embryology, Kidney, Bladder, and Ureter - StatPearls - NCBI Bookshelf](https://www.ncbi.nlm.nih.gov/books/NBK547747/) (StatPearls Publishing (NCBI Bookshelf), 2023). ## **Spotted a mistake?** We are always improving for the community. Tell us what is wrong and our team will review it. Report a mistake Representative model, for educational purposes only. --- Source: https://durgical.com/en/embryology/duplicated-ureter-upj-obstruction-and-posterior-urethral-valves/ License: CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). Cite as: DurgiPedia (durgical.com), https://durgical.com/en/embryology/duplicated-ureter-upj-obstruction-and-posterior-urethral-valves/