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Type:
Educational Exhibit
Keywords:
Urinary Tract / Bladder, CT, Ultrasound, Diagnostic procedure, Education and training
Authors:
V. S. Teran Pareja, A. Martínez Arnaiz, N. Guerrero Salcedo, E. Prado Miranda, E. Rico Aragón, E. Martínez Carapeto; Madrid/ES
DOI:
10.1594/ecr2015/C-2538
Background
The urachus,
also known as median umbilical ligament, is a remnant of the development of two embryonic structures: the cloaca,
which is the cephalic extension of the urogenital sinus,
and the allantois,
which is a derivative of the yolk sac. Fig. 1
Between the fourth and seventh week of life,
the cloaca becomes divided into two embryological structures: the anorectal canal posteriorly and the primitive urogenital sinus anteriorly.
The cephalic extension of the urogenital sinus will be the precursor of the fetal bladder,
which is contiguous with the allantois ventrally at the level of the umbilicus; thus,
the bladder initially extends all the way to the umbilicus.
By the fourth or fifth month of pregnancy,
the apical bladder portion progressively looses its lumen and becomes converted into a fibrous,
cord-like structure which persists in the adult as the median umbilical.
Fig. 2
The urachus varies from 3 to 10 cm long and 8 to 10 mm in diameter.
It lies in the space of Retzius,
between the transversalis fascia anteriorly,
the peritoneum posteriorly,
and the umbilical ligaments,
which are remnants of fetal umbilical arteries,
located on both sides.
Occasionally,
it may merge with one or both of the obliterated umbilical arteries,
and may have a slight deviation to the right or left of the midline.
Urachal arteries arise from the superior vesical.
Fig. 3
Histologically is a three-layered tubular structure,
the innermost layer being lined with transitional epithelium in 70% of cases and with columnar epithelium in 30%.
The structure is surrounded by connective tissue and an outermost muscle layer in continuity with the detrusor muscle.