Urachus

Urachus
Vertical section of bladder, penis, and urethra. Urachus is seen at top
Urachus is #1
Identifiers
MeSH	A16.254.835
*Anatomical terminology* []

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 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.

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:

The urachus is also subject to neoplasia. Urachal adenocarcinoma is histologically similar to adenocarcinoma of the bowel.

One urachal mass has been reported that was found to be a manifestation of IgG4-related disease.

Inguinal fossae

CT scan (sagittal reconstruction) showing an urachus rest as an incidental finding in a 44-year-old man, the trajectory moves forward and upward from the bladder to the umbilicus in the midline.

Ultrasound of fetus showing urachus duct from bladder to the umbilicus.

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