Urachus

{{Short description|Structure of the urinary system}} {{confuse|Vitelline duct}} {{Infobox embryology | Name = Urachus | Latin = | Image = Gray1156.png | Caption = Vertical section of bladder, penis, and urethra. Urachus is seen at top | Image2 = Illu quiz bladder 01.jpg | Caption2 = Urachus is #1 | System = | CarnegieStage = | Days = | Precursor = | GivesRiseTo = }} The '''urachus''' forms from the distal end of the allantois in the embryo, and develops into a closed cord between the base of the bladder, and the navel.<ref name="Terms">{{cite web |title=Urachus |url=https://www.cancer.gov/publications/dictionaries/cancer-terms/def/urachus |website=www.cancer.gov |access-date=21 December 2024 |language=en |date=2 February 2011}}</ref> It drains the bladder of the fetus that joins and runs within the umbilical cord.<ref>Larsen, "Human Embryology," 3rd ed., pg. 258</ref> The fibrous remnant lies in the space of Retzius, between the transverse fascia anteriorly and the peritoneum posteriorly. At birth, the urachus develops into the median umbilical ligament.<ref name="Tan">{{cite journal |vauthors=Tan C, Simon MA, Dolin N, Gesner L |date=August 2020 |title=Incidental vesicourachal diverticulum in a young female |url= |journal=Radiology Case Reports |volume=15 |issue=8 |pages=1305–1308 |doi=10.1016/j.radcr.2020.05.046 |pmc=7322240 |pmid=32612730}}</ref><ref name="Mrad">{{cite journal |vauthors=Mrad Daly K, Ben Rhouma S, Zaghbib S, Oueslati A, Gharbi M, Nouira Y |date=September 2019 |title=Infected urachal cyst in an adult: A case report |url= |journal=Urology Case Reports |volume=26 |article-number=100976 |doi=10.1016/j.eucr.2019.100976 |pmc=6661533 |pmid=31380223}}</ref>

==Development== The part of the urogenital sinus related to the bladder and urethra absorbs the ends of the Wolffian ducts and the associated ends of the renal diverticula. This gives rise to the trigone of the bladder and part of the prostatic urethra.

The remainder of this part of the urogenital sinus forms the body of the bladder and part of the prostatic urethra. The apex of the bladder stretches and is connected to the umbilicus as a narrow canal. This canal is initially open, but later closes as the urachus goes on to definitively form the median umbilical ligament.

==Clinical significance== Failure of the inside of the urachus to be filled in leaves the urachus open. The telltale sign is leakage of urine through the umbilicus. This is often managed surgically. There are four anatomical causes: # Urachal cyst: there is no longer a connection between the bladder and the umbilicus, however a fluid filled cavity with uroepithelium lining persists between these two structures. # Urachal fistula: there is free communication between the bladder and umbilicus # Urachal diverticulum (vesicourachal diverticulum): the bladder exhibits outpouching<ref> {{Cite book |last1=Le |first1=Tao |url=https://archive.org/details/firstaidforusmle0000unse_r6p4/page/122 |title=First Aid for the USMLE Step 1: 2010 |last2=Bhushan |first2=Vikas |last3=Vasan |first3=Neil |publisher=The McGraw-Hill Companies, Inc. |year=2010 |isbn=978-0-07-163340-6 |edition=20th Anniversary |location=US |pages=[https://archive.org/details/firstaidforusmle0000unse_r6p4/page/122 122] |url-access=registration}} </ref> # Urachal sinus: the pouch opens toward the umbilicus<ref>Guray, Sogut, et al. (2000) Urachal Cyst. Eastern Journal of Medicine 5(2):76-78.</ref>

The urachus is also subject to neoplasia. Urachal adenocarcinoma is histologically similar to adenocarcinoma of the bowel. Rarely, urachus carcinomas can metastasise to other regions of the body, including pelvic bones and the lung.<ref>{{cite journal |last1=Elser |first1=C |last2=Sweet |first2=J |last3=Cheran |first3=S K |last4=Haider |first4=M A |last5=Jewett |first5=M |last6=Sridhar |first6=S S |title=A case of metastatic urachal adenocarcinoma treated with several different chemotherapeutic regimens |journal=Can Urol Assoc J |date=February 2012 |volume=6 |issue=1 |pages=E27–E31 |doi=10.5489/cuaj.11109 |pmid=22396380 |pmc=3289708 |doi-broken-date=12 July 2025 }}</ref>

One urachal mass has been reported that was found to be a manifestation of IgG4-related disease.<ref name=pmid25202466> {{cite journal |author1=Travis W. Dum |author2=Da Zhang |author3=Eugene K. Lee |date=2015 |title=IgG4-Related Disease in a Urachal Tumor |journal=Case Reports in Urology |volume=2015 |id=275850 |article-number=275850 |doi=10.1155/2014/275850 |pmc=4151357 |pmid=25202466|doi-access=free }} </ref>

==Additional images== <gallery> File:Inguinal fossae.PNG|Inguinal fossae File:Urachusrest im CT sagittal - 44Jahre - Zufallsbefund.jpg|Midsagittal CT scan of a man's abdomen showing the urachus File:Normal fully developed bladder with urachus and four of the most common urachal anomaly subtypes including patent urachus, vesicourachal diverticulum, urachal cyst, and umbilical-urachal.png|The normal urachus and its anomalous variants File:Urachal carcinoma - high mag.jpg|High magnification micrograph of a urachal carcinoma. H&E stain </gallery>

==References== {{Gray's}} {{Reflist}}

==External links== * {{EmbryologySwiss|turinary/patholurinary07}} * [https://web.archive.org/web/20060211184745/http://www.moorabbinvet.com.au/tour/pages/urachus.html "Persistent urachus" at Moorabbin Veterinary Hospital] * [http://www.pennhealth.com/health_info/Surgery/patenturachusrepair_4.html "Patent Urachus Repair" at Penn Medicine]

Category:Embryology of urogenital system