[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) › Urachal anomalies: patent urachus, cyst and sinus [Embryology](https://durgical.com/en/embryology/) · [Urogenital system](https://durgical.com/en/embryology/#a-urogenital) # 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](https://durgical.com/en/anatomy/urinary-bladder/) ## Key points - Patent urachus: an open channel between bladder and navel; urine leaks from the navel. - Urachal cyst: both ends close and the middle stays open; it shows up when infected. - Umbilical sinus: open only to the navel; vesicourachal diverticulum: open only to the bladder. - A patent urachus calls for a search for lower urinary obstruction, such as posterior urethral valves. - In adults the urachal remnant can give adenocarcinoma of the bladder dome. - Differential of a wet navel: a patent omphalomesenteric duct, which drains bowel content. ## 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. ## Memory aid “Open end to end, it drips; closed at both ends, it swells; open at the top, it weeps; open at the bottom, it is a pocket of the bladder.” ## 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). [Add to my cards (4)](https://durgical.app/estudiar/?add=/en/embryology/urachal-anomalies-patent-urachus-cyst-and-sinus/) ## See it in 3D The structures of Durgical's 3D anatomy where it is found. - [Urinary bladder](https://durgical.com/en/anatomy/urinary-bladder/) ## Related - [Bladder, urachus and urethra](https://durgical.com/en/embryology/bladder-urachus-and-urethra/) - [Fetal membranes: amnion, chorion, yolk sac and allantois](https://durgical.com/en/embryology/fetal-membranes-amnion-chorion-yolk-sac-and-allantois/) - [Umbilical cord: two arteries, one vein](https://durgical.com/en/embryology/umbilical-cord-two-arteries-one-vein/) - [Meckel diverticulum and other vitelline duct remnants](https://durgical.com/en/embryology/meckel-diverticulum-and-other-vitelline-duct-remnants/) - [Duplicated ureter, UPJ obstruction and posterior urethral valves](https://durgical.com/en/embryology/duplicated-ureter-upj-obstruction-and-posterior-urethral-valves/) - [Poland sequence and prune belly syndrome](https://durgical.com/en/embryology/poland-sequence-and-prune-belly-syndrome/) ## Related conditions - [Urinary tract infection (acute cystitis)](https://durgical.com/en/conditions/urinary-tract-infection/) - [Bladder cancer](https://durgical.com/en/conditions/bladder-cancer/) [← 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: [Patent Urachus - StatPearls - NCBI Bookshelf](https://www.ncbi.nlm.nih.gov/books/NBK557723/) (StatPearls Publishing (NCBI Bookshelf), 2023); [Embryology, Genitourinary - StatPearls - NCBI Bookshelf](https://www.ncbi.nlm.nih.gov/books/NBK559309/) (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/urachal-anomalies-patent-urachus-cyst-and-sinus/ License: CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). Cite as: DurgiPedia (durgical.com), https://durgical.com/en/embryology/urachal-anomalies-patent-urachus-cyst-and-sinus/