and Spencer W. Beasley2
(1)
Department of Urology, Royal Children’s Hospital, Melbourne, Australia
(2)
Paediatric Surgery Department Otago, University Christchurch Hospital, Christchurch, New Zealand
Abstract
After introducing the embryology, we describe the clinical diagnosis of the different presentations: weeping of mucus, faeces or urine. There is a description of how to assess exomphalos (omphalocele) and gastroschisis, and sections on umbilical and epigastric hernia.
In the embryo, the primitive umbilical ring is a relatively large defect in the ventral abdominal wall transmitting a number of structures which connect the fetus to the cord and placenta (Fig. 6.1). In the 5-week embryo, the mid-gut communicates with the yolk sac via the vitelline duct or yolk stalk. The yolk sac provides an early nutrient source for the embryo. In the next few weeks, the mid-gut develops more rapidly than the abdominal cavity and herniates through the umbilical ring into the extra-embryonic coelom (Fig. 6.2). By 10 weeks, the mid-gut has returned to the abdominal cavity and the vitelline duct subsequently degenerates (Fig. 6.3). If the vitelline duct does not involute, a vitello-intestinal fistula may result.
Fig. 6.1
The structures which pass through the umbilical ring
Fig. 6.2
Herniation of the mid-gut through the primitive umbilical ring in the 6-week embryo
Fig. 6.3
Return of the mid-gut to the abdominal cavity with rotation in the 10-week embryo
Partial degeneration may result in a sinus, cyst or fibrous band connecting the ileum to the underside of the umbilicus. Continued growth of the duct at the intestinal wall produces a Meckel’s diverticulum (Fig. 6.4). Failure of the mid-gut to re-enter the abdomen from the umbilical cord, or reherniation through the umbilical ring at a later stage, results in exomphalos. In this condition, the intestines and liver protrude through the abnormal umbilical ring into a thin avascular sac between the body wall and cord.
Fig. 6.4
Malformations caused by a persistent vitelline duct. These range from a Meckel’s diverticulum (a), a blind-ending umbilical sinus (b), or cyst (c). Rarely there may be a complete vitello-intestinal duct (d), or a fibrous band (e). The vitello-intestinal duct predisposes to prolapse of the mucosa through the umbilicus (b)
Another structure passing through the umbilical ring is the allantois, which contributes to the formation of the bladder after initial outgrowth from the hindgut into the body stalk.
The part of the allantois extending from the umbilicus to the bladder is called the urachus, but this structure is vestigial in man and its lumen closes well before 10 weeks of development. The fibrous cord so formed persists into adult life as the median umbilical ligament, running between the peritoneum and transversalis fascia from the dome of the bladder to the umbilicus.
Failure of the urachus to obliterate results in urinary discharge from the umbilicus and can be associated with bladder outflow obstruction. Patency of one part of the urachus produces a urachal diverticulum, sinus or cyst (Fig. 6.5).
Fig. 6.5
Urachal malformations. These include simple patency (a), a urachal sinus at the umbilicus (b), or a urachal cyst (c). Sometimes there is a diverticulum at the apex of the bladder (d). Urachal anomalies may become infected to form an abscess (e)
As the fetus grows, the umbilical ring remains constant, making it appear relatively smaller. At birth, the umbilical vessels are the only major structures in the cord, and when they involute, the umbilical ring becomes empty. If the ring does not constrict quickly, some of the contents of the abdomen may herniate through the skin-covered defect, a week or so after birth, as an umbilical hernia. These herniae tend to become smaller with time, such that 90 % have disappeared by 1 year of age.
After separation of the umbilical cord, the exposed surface of the stump may become infected with the formation of sessile or pedunculated granulation tissue, the ‘umbilical granuloma’, which looks pink and moist. A similar appearance is produced by ectopic mucosa which represents persistence of the umbilical part of the vitelline tract.
In the uncommon condition of gastroschisis, the intestines protrude through a defect in the ventral abdominal wall immediately to the right of the umbilicus and are not covered by peritoneum or skin.
Clinical Diagnosis
Is the Umbilicus Abnormal?
At birth, the umbilical cord is clamped and divided several centimetres from the umbilical ring. Over the next week, it desiccates and separates from the umbilicus. The umbilicus dries rapidly and appears as a corrugated dimple about 1 cm in diameter. Apart from an umbilical hernia, the commonest abnormality of the umbilicus is a persistent discharge which commences after detachment of the umbilical cord stump. More major umbilical abnormalities present as passage of urine or faeces from the umbilicus through a sinus opening or as the obvious defects of exomphalos and gastroschisis.
The Weeping Umbilicus
The umbilicus dries within days of separation of the umbilical cord stump. If it remains moist and there is a weeping discharge from granulation tissue at its base, an umbilical granuloma should be suspected. This condition is diagnosed on clinical grounds and requires no further investigation. However, several points must be considered before a diagnosis of umbilical granuloma is made. First, it should not have urine or faecal discharge; if these are present, the umbilicus should be examined carefully for evidence of a sinus or fistula opening. This may lie at the base and may be concealed in part by the rest of the umbilicus. Secondly, age is of some significance in that an umbilical granuloma develops in the first month or two of life, whereas sinuses and cysts of urachal and vitelline origin usually appear at a later date. Thirdly, an umbilical granuloma is not associated with other congenital abnormalities, since it represents subacute infection of the necrotic cord stump.
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