Vertical section of bladder, penis, and urethra. Urachus is seen at top
Urachus is #1
The urachus is a fibrous remnant of the allantois, a canal that drains the urinary bladder of the fetus that joins and runs within the umbilical cord. The fibrous remnant lies in the space of Retzius, between the transversalis fascia anteriorly and the peritoneum posteriorly.
The vesico-urethral portion of the urogenital sinus absorbs the ends of the Wolffian ducts and the associated ends of the renal diverticula, and these give rise to the trigone of the bladder and part of the prostatic urethra. The remainder of the vesico-urethral portion forms the body of the bladder and part of the prostatic urethra; its apex is prolonged to the umbilicus as a narrow canal, which later is obliterated as the urachus goes on to definitively form the median umbilical ligament (urachus).
Failure for the lumen of the urachus to be filled in leaves a patent (open) urachus. The telltale sign is leakage of urine through the umbilicus. A patent urachus needs to be surgically removed. There are four anatomical causes:
- Urachal cyst: there is no connection between the bladder and the umbilicus
- Urachal fistula: there is free communication between the bladder and umbilicus
- Urachal diverticulum [Vesicourachal diverticulum]: the bladder exhibits outpouching
- Urachal sinus: the pouch opens toward the umbilicus
The urachus is also subject to neoplasia. Urachal adenocarcinoma is histologically similar to adenocarcinoma of the bowel.
- Larsen, "Human Embryology," 3rd ed., pg. 258
- Le, Tao; Bhushan, Vikas; Vasan, Neil (2010). First Aid for the USMLE Step 1: 2010 (20th Anniversary ed.). USA: The McGraw-Hill Companies, Inc. p. 122. ISBN 978-0-07-163340-6.
- Guray, Sogut, et al. (2000) Urachal Cyst. Eastern Journal of Medicine 5(2):76-78.
- Swiss embryology (from UL, UB, and UF) turinary/patholurinary07
- Persistent urachus at moorabbinvet.com.au
- Repair at pennhealth.com
- Vesico-urachal Diverticulum Radiology (CT Images)
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