Omphalocele

Omphalocele is a congenital anterior abdominal wall defect in which the intestines are covered by peritoneum and amniotic membranes. The condition results from the failure of the midgut to return to the abdominal cavity by 10 weeks’ gestation. Omphalocele is frequently associated with genetic syndromes and chromosomal abnormalities. Prenatal diagnosis can be made by prenatal ultrasound, maternal blood elevated ⍺-fetoprotein, and fetal chromosomal analysis. Treatment includes immediate hemodynamic stabilization followed by primary or staged surgical repair.

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Overview

Definition

  • A congenital defect of the anterior abdominal wall located at the base of the umbilicus in which the intestine and other abdominal viscera are only covered by the peritoneum and amniotic membranes
  • Giant omphalocele measure ≥ 4 cm, contain the liver, and are associated with small undeveloped abdominal and thoracic cavities.
Omphalocele containing OMD cyst

Large omphalocele containing omphalomesenteric duct cyst

Image: “Large omphalocele containing OMD cyst” by Yousuf Aziz Khan, MBBS, FCPS (Paediatric Surgeon), Department of Paediatric Surgery, National Institute of Child Health, Rafiquee Shaheed Road, Karachi – 75510, Sind, Pakistan. License: CC BY 3.0

Embryology

  • Gastrointestinal (GI) system development from 3 germinal layers:
    • Mesoderm: connective tissue (wall of gut tube, blood vessels, smooth muscle)
    • Endoderm: epithelial lining
    • Ectoderm: epidermis and neural crest (neurons of the GI tract)
  • GI tract divisions:
    • Foregut: oral cavity to 1st part of the duodenum
    • Midgut: mid-duodenum to 1st ⅔ of the transverse colon
    • Hindgut: last ⅓ of the transverse colon to upper anus
  • 6th week of gestation:
    • Rapid growth of GI tract
    • Midgut herniates through umbilical ring, developing entirely outside the peritoneal cavity.
  • 10th week of gestation:
    • Abdominal cavity is large enough for developing midgut.
    • Midgut completes rotation and returns to abdominal cavity.
Normal process of herniation during embryologic development

Diagram showing the normal process of intestinal rotation and herniation during embryologic development
A: The midgut (multi-colored loop) before herniation
B1–B3: As it grows rapidly, the midgut herniates through the umbilical ring and begins rotation.
C: The midgut returns to the abdominal cavity.

Image by Lecturio.

Epidemiology

  • Prevalence: 1 in 5,000 births
  • Boys > girls
  • Seen more commonly with younger or older mothers (< 20 or > 40 years old)
  • More prevalent in Black patients
  • 60%70% have associated abnormalities, including cardiac and chromosomal. 
  • May occur as part of syndromes:
    • Beckwith-Weidemann constellation of anomalies (macroglossia, macrosomia, hypoglycemia, visceromegaly, and omphalocele)
    • Cantrell’s pentalogy (cleft sternum, ectopia cordis, anterior midline diaphragmatic hernia, cardiac anomalies, epigastric omphalocele)
    • Trisomy 13, 18, or 21
    • Cloacal exstrophy (vesicointestinal fissure)
  • May be associated with prematurity, intrauterine growth restriction
  • Often seen in familial clustering

Pathophysiology

Pathophysiology is not definitively understood; 2 main theories:

  • Failure of the midgut to return to the abdominal cavity by 10 weeks’ gestation results in omphalocele
  • Failure of abdominal folds to seal, leaving midline defect and externalized abdominal organs

Diagnosis

Most cases of omphalocele (90%) are diagnosed prenatally:

  • Ultrasound: 
    • Part of routine prenatal screening
    • Can show other associated abnormalities 
  • Maternal serum ⍺-fetoprotein levels: Elevated levels are non-specific signs of omphalocele.
  • If detected prenatally, parents should be offered: 
    • Testing for Beckwith-Wiedemann syndrome
    • Microarray chromosomal analysis to evaluate for aneuploidy and trisomies 
    • Prenatal echocardiogram

Clinical Presentation

  • Newborn findings:
    • Full-thickness ventral wall defect
    • Herniation of intestines through umbilical ring, may also contain abdominal organs
    • Covered in clear sac composed of amniotic membrane and peritoneum
    • Size usually varies from 4–12 cm 
    • Occur centrally, in epigastrium, or in hypogastrium
  • Delivery can be challenging and requires a specialist.
    • Rupture of omphalocele sac can occur in ⅕ of cases.
    • Umbilical cord clamping must be carefully done to avoid damaging intestinal structures.

Management

Perinatal management

  • Attend to vital signs and evaluate respiratory distress (due to lung hypoplasia).
  • Avoid pressure and manual reduction.
  • Cover omphalocele with non-moist dressing.
  • Screen for hypoglycemia, associated with Beckwith-Weidemann syndrome.
  • Apply nasogastric tube decompression.
  • Administer prophylactic broad-spectrum antibiotics in case of rupture.
  • Perform echocardiogram prior to any surgical procedure.

Surgery

  • Small-to-medium–sized defects with normal lung: early (within 24 hrs) primary repair (resection of membrane and closure of defect)
  • Giant omphalocele: multi-staged procedure to allow intra-abdominal accommodation and pulmonary maturation 
  • Enteral feeding can be established very early after closure.

Differential Diagnosis

  • Gastroschisis: a full-thickness defect of the anterior abdominal wall through which the intestine and/or other abdominal viscera freely protrude. No membrane or sac covers the bowel/intestine. Diagnosis is via prenatal ultrasound and treatment is surgical after birth. Gastroschisis is not commonly associated with other birth defects.
  • Pentalogy of Cantrell: a rare syndrome consisting of multiple congenital abnormalities, including a lower sternal defect, anterior diaphragm defect, pericardial defect, abdominal wall defect, and congenital heart anomalies. Diagnosis is made prenatally by ultrasonography. Treatment requires complex medical and surgical care.
  • Bladder exstrophy-epispadias complex: a spectrum of congenital defects: epispadias (failed closure of urethra), bladder exstrophy, and cloacal exstrophy (most severe defect, which includes anal atresia and omphalocele). Treatment is surgical, with goals to close abdominal wall defect, achieve urinary continence, and reconstruct genito-urinary area.
  • Umbilical hernia: presents as a protrusion in the neonate’s umbilical area. There is incomplete closure of the fascia of the umbilical ring, but with intact skin covering the ring. It is important to determine the reducibility, as incarcerated hernia is a complication. Surgery is indicated for defects > 1.5 cm in those > 2 years of age and for complications such as strangulation, incarceration, or rupture.

References

  1. Stallings EB et al. (2019). Population-based birth defects data in the United States, 20122016: A focus on abdominal wall defects. Birth Defects Res. doi: 10.1002/bdr2.1607
  2. Marshall J et al. (2015). National Birth Defects Prevention Network. Prevalence, Correlates, and Outcomes of Omphalocele in the United States, 1995-2005. doi: 10.1097/AOG.0000000000000920
  3. Bhatia, A., Shatanof, R., Bordoni, B. (2020). Embryology, Gastrointestinal. StatPearls. https://www.ncbi.nlm.nih.gov/books/NBK537172/ 
  4. Roux N et al. (2018). Early surgical management for giant omphalocele: Results and prognostic factors. J Pediatr Surg. doi: 10.1016/j.jpedsurg.2018.04.036
  5. Glasser, J., Windle, M., Carter, B. (2019). Pediatric Omphalocele and Gastroschisis (Abdominal wall defects). Medscape. Retrieved 4 Oct 2020, from https://emedicine.medscape.com/article/975583-overview#a5

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