The urachus is a fibrous remnant of the

allantois The allantois (plural ''allantoides'' or ''allantoises'') is a hollow sac-like structure filled with clear fluid that forms part of a developing amniote's conceptus (which consists of all embryonic and extraembryonic tissues). It helps the embryo ...

, a canal that drains the

urinary bladder The urinary bladder, or simply bladder, is a hollow organ in humans and other vertebrates that stores urine from the kidneys before disposal by urination. In humans the bladder is a distensible organ that sits on the pelvic floor. Urine enters ...

of the fetus that joins and runs within the

umbilical cord In placental mammals, the umbilical cord (also called the navel string, birth cord or ''funiculus umbilicalis'') is a conduit between the developing embryo or fetus and the placenta. During prenatal development, the umbilical cord is physiologic ...

. The fibrous remnant lies in the

space of Retzius Retropubic space is a potential avascular space located between the pubic symphysis and the urinary bladder. The retropubic space is a preperitoneal space, located behind the transversalis fascia and in front of peritoneum . Other names for the ...

, between the

transverse fascia The transversalis fascia (or transverse fascia) is a thin aponeurotic membrane of the abdomen. It lies between the inner surface of the transverse abdominal muscle and the parietal peritoneum. It forms part of the general layer of fascia lining ...

anteriorly and the

peritoneum The peritoneum is the serous membrane forming the lining of the abdominal cavity or coelom in amniotes and some invertebrates, such as annelids. It covers most of the intra-abdominal (or coelomic) organs, and is composed of a layer of mesoth ...

posteriorly.

Development

The part of the

urogenital sinus The urogenital sinus is a part of the human body only present in the development of the urinary and reproductive organs. It is the ventral part of the cloaca, formed after the cloaca separates from the anal canal during the fourth to seventh we ...

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 prostatic urethra, the widest and most dilatable part of the urethra canal, is about 3 cm long. It runs almost vertically through the prostate from its base to its apex, lying nearer its anterior than its posterior surface; the form of ...

. 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 In human anatomy, the median umbilical ligament is an unpaired midline ligamentous structure upon the lower inner surface of the anterior abdominal wall. It is covered by the median umbilical fold. The median umbilical ligament represents the re ...

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 A urachal fistula is a congenital disorder caused by the persistence of the allantois (later, urachus), the structure that connects an embryo's bladder to the yolk sac. Normally, the urachus closes off to become the median umbilical ligament; howe ...

: there is free communication between the bladder and umbilicus *

Urachal diverticulum A urachal diverticulum (also ''vesicourachal diverticulum'') is a congenital disorder caused by the partial persistence of the allantois. The allantois, which later becomes the urachus, connects an embryo's bladder to the yolk sac. Normally, the u ...

esicourachal 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. Rarely, urachus carcinomas can metastasise to other regions of the body, including pelvic bones and the lung. One urachal mass has been reported that was found to be a manifestation of

IgG4-related disease IgG4-related disease (IgG4-RD), formerly known as IgG4-related systemic disease, is a chronic inflammatory condition characterized by tissue infiltration with lymphocytes and IgG4-secreting plasma cells, various degrees of fibrosis (scarring) and ...

Additional images

File:Inguinal fossae.PNG, Inguinal fossae

References

External links

*
Persistent urachus at moorabbinvet.com.au

{{Portal bar, Anatomy Embryology of urogenital system