The urachus is a fibrous remnant of the
allantois, 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 ente ...
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 physiologi ...
. 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 meso ...
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 w ...
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 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