Etiology
The umbilical cord is composed of the umbilical vein, paired umbilical arteries, vitelline duct, and the allantois. These structures traverse the abdominal wall through the umbilical ring, a defect in the dense fascia of the linea alba. This ring normally closes by contracture after the cord is ligated and the umbilical vessels thrombose. When this ring fails to close, an umbilical hernia can protrude through the remaining fascial defect. The umbilical vein obliterates and becomes a fibrous cord known as the round ligament of the liver. This typically attaches to the inferior margin of the umbilical ring and provides strength to the umbilicus and protection from umbilical hernia. In approximately 25% of infants the round ligament attaches to the superior border of the umbilical ring.[4] This leaves an attenuated umbilical floor, composed of only peritoneum and umbilical fascia (a thickening of the transversalis fascia), which allows the infant to develop an umbilical hernia.
Pathophysiology
Most umbilical hernias are recognized shortly after birth, after the cord sloughs and the umbilicus heals. They are rarely symptomatic. The umbilical ring continues to close over time and the umbilical fascia strengthens, resulting in spontaneous resolution of the defect in most children. One study found that defects <0.4 inches (<1 cm) in diameter have an 80% chance of spontaneous closure.[5] Another study found that despite 89.1% of hernias resolving spontaneously by age 6, the odds of spontaneous closure decreased by 5% for every 1 mm increase in defect size (up to 1 cm).[6] However, a study from Nigeria reported that spontaneous closure was still possible up to 14 years of age.[3]
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