Embryology · Urogenital system
Urachal anomalies: patent urachus, cyst and sinus !
- Malformation
The urachus linked the bladder to the navel and should close; if it stays open in whole or part, urine can leak or a cyst can form.
Updated 2026-11-01
See it in 3D: Urinary bladder
What it is
The urachus is the remnant of the allantois joining the bladder dome to the navel; it normally becomes the median umbilical ligament. If it fails to obliterate completely, four variants appear: patent urachus, urachal cyst, umbilical sinus and vesicourachal diverticulum. They are rare, but a wet navel in a newborn and an infected mass below the navel are classic presentations.
Embryological cause
- Weeks 4–7: as the cloaca divides, the upper urogenital sinus (bladder) remains joined to the allantois.
- The intraembryonic allantois narrows into the urachus, which obliterates toward the end of gestation.
- If obliteration fails along its whole length, the urachus stays patent; if it fails in one segment, a cyst, sinus or diverticulum results.
- Bladder outlet obstruction raises pressure and can keep the urachus open.
How it presents
- Patent urachus: a navel that drips urine, more with crying or straining; periumbilical dermatitis; a thick cord or one slow to separate.
- Infected cyst: lower midline pain, fever, a palpable midline mass and periumbilical cellulitis.
- Umbilical sinus: persistent discharge or an umbilical polyp.
- Vesicourachal diverticulum: often silent; it can favour infection or stones.
- A patent urachus is described in a share of children with prune belly syndrome.
Diagnosis
- Ultrasound: the first test; shows the tract or cyst between navel and bladder.
- Creatinine of the fluid draining from the navel: confirms it is urine.
- Voiding cystourethrogram for a patent urachus: looks for reflux and posterior urethral valves.
- CT in adults or unclear cases.
Test yourself
Think of the answer, then tap the question to see it.
Which embryonic structure does the urachus come from, and what does it become?
The allantois; it normally obliterates to form the median umbilical ligament.
What does urine leaking from a newborn's navel suggest?
A patent urachus: an open channel between the bladder dome and the navel.
Why is a urethral obstruction sought when a urachus is patent?
Because a lower obstruction, such as posterior urethral valves, raises bladder pressure and can keep the urachus open as an escape route.
Which cancer is linked to urachal remnants in adults?
Adenocarcinoma of the bladder dome (urachal carcinoma).
See it in 3D
The structures of Durgical's 3D anatomy where it is found.
Related
- Bladder, urachus and urethra
- Fetal membranes: amnion, chorion, yolk sac and allantois
- Umbilical cord: two arteries, one vein
- Meckel diverticulum and other vitelline duct remnants
- Duplicated ureter, UPJ obstruction and posterior urethral valves
- Poland sequence and prune belly syndrome
Related conditions
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: Patent Urachus - StatPearls - NCBI Bookshelf (StatPearls Publishing (NCBI Bookshelf), 2023); Embryology, Genitourinary - StatPearls - NCBI Bookshelf (StatPearls Publishing (NCBI Bookshelf), 2023).
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Representative model, for educational purposes only.