Omphalocele is a congenital midline abdominal wall defect, typically presenting at birth with herniation of abdominal organs into a sac covered by a translucent membrane outside the abdominal cavity.
Description
Omphalocele, also known as exomphalos, is a congenital defect of the anterior abdominal wall in which the abdominal organs herniate into a membranous sac. This sac is formed from the peritoneum and amnion. It is one of the most common congenital abdominal wall defects in neonates and is often associated with other congenital anomalies.
Pathogenesis
During normal embryonic development, the midgut herniates into the umbilical cord around the sixth week due to rapid growth. By the tenth week, as the abdominal cavity expands, the midgut returns, completing a 270-degree rotation. In omphalocele, this return fails, resulting in a persistent physiological midgut herniation. Therefore, the abnormality is only identified on the second-trimester scan. The defect is covered by a sac of peritoneum and amnion and may contain other abdominal organs, depending on the severity. The most common extracorporeal organ is the liver.
Subtypes
There are no recognised subtypes of omphalocele.
Epidemiology, Risk Factors & Associations
- The incidence of omphalocele is approximately 1 in 4,000 live births (0.025%).
- Associated with chromosomal abnormalities (30%) – Trisomies 13, 18, and 21 (Patau, Edwards, and Down syndromes respectively). This risk increases if omphalocele contains bowel only.
- Approximately 40-50% of omphalocele cases are associated with additional congenital anomalies or syndromes. Associations include
- Beckwith-Wiedemann syndrome (overgrowth disorder; incidence 1 in 13,700 newborns, approximately 0.007%)
- Pentalogy of Cantrell (rare collection of five congenital midline birth anomalies including: supraumbilical omphalocele, lower sternal cleft, defect in the central tendon of the diaphragm, defect in the pericardium, intracardiac anomaly; incidence approximately 5.5 in 1 million live births, approximately 0.00055%)
- OEIS complex (omphalocele, exstrophy, imperforate anus, spinal defects; extremely rare with fewer than 200 cases reported in the medical literature)
- A correlation with advanced maternal age has been observed, with a higher incidence noted in mothers over 35.
- Risk is increased with maternal use of certain substances or medications during pregnancy such as alcohol, tobacco, or certain antiepileptic drugs.
Clinical Features
- Herniation of the abdominal organs into an exterior sac at birth
- The size of the defect can vary, with small omphaloceles containing only a portion of the intestine, while large ones can include the liver and other abdominal organs.
Complications
- Potential for organ damage or infection if the sac ruptures
- Associated anomalies or syndromes can present their own range of complications
Pathological Features
Histopathology
- Macroscopic: External sac containing herniated organs
- Microscopic: Not applicable as omphalocele is a gross anatomical defect
Serology
- Chromosomal analysis may be performed if a genetic syndrome is suspected
Biochemistry
- Raised maternal alpha-fetoprotein (MSAFP)
Radiological Features
General Features
- Prenatal ultrasound typically reveals the herniated abdominal organs within an external sac. Usually detected at 1st trimester screen when foetal cord insertion is assessed. Extracorporeal bowel is not seen after 12 weeks and normal liver is never extracorporeal.
- Associated anomalies can be detected is more likely if liver is not involved.
- A ruptured omphalocele membrane appears as free-floating bowel which can mimic gastroschisis. Presence of eviscerated liver and a generally larger abdominal defect favours omphalocele.
US
- B-mode:
- Smoothly contoured midline abdominal wall defect with covering membrane.
- Herniation of abdominal contents into the sac can be seen, liver and small bowel are most commonly seen. Larger defects may include spleen, bladder, and stomach.
- Herniated bowel appears echogenic (due to collapse) and may demonstrate peristalsis. Herniated superior mesenteric artery may also be seen.
- Herniated liver demonstrates hepatic vessels or ductus venosus.
- Covering membrane formed by inner peritoneum, Wharton jelly, then outer amnion. May have a multicystic appearance due to cystic degeneration of Wharton jelly.
- Allantoic cyst is often present
- Intrauterine growth restriction
- Colour Doppler: Demonstrates umbilical cord insertion directly into membrane of omphalocele, which may be central or eccentric in location.
Diagnosis
- The diagnosis is usually made antenatally with prenatal ultrasound
- Postnatally, the diagnosis is clinical, based on the characteristic appearance of the omphalocele at birth
Differential Diagnosis
- Gastroschisis: Paraumbilical abdominal wall defect without a covering sac, usually to the right of the umbilicus. Bowel is free-floating, often inflamed and matted, which is not seen in omphalocele. Cord inserts normally on abdominal wall. Presence of extracorporeal liver signifies poor prognosis.
- Physiological midgut herniation: Normal in early pregnancy and resolves by 12 weeks
- Umbilical cord cyst: Can mimic bowel herniation, usually self-resolving. May co-exist with omphalocele (omphalomesenteric duct cyst). Allantoic cysts associated with patent urachus, always seen near foetal insertion site. Mucoid degeneration of Wharton jelly can also be seen with omphalocele.
Prognosis
- Prognosis depends on the size of the omphalocele, associated anomalies or syndromes, and any complications such as infection or organ damage
Management
- Pediatric surgery consultation is necessary, with surgical repair of the defect typically performed
- Supportive care, including maintenance of body temperature and fluid balance, and prevention of infection, is crucial