omphalocele (exomphalos)
description
the gut normally returns to the abdominal cavity by the 10th week of gestation, undergoing rotation at this time. omphalocele results when this process fails, and has an incidence of about 1 in 5000 live births. the defect comprises a herniation of intraabdominal contents within the umbilical stalk, covered by a layer of peritoneum and amnion. the severest consequences are associated with failure of the closure of the lateral fold at 4 weeks gestation, resulting in a very large abdominal wall defect which may include bladder exstrophy. after postnatal repair of the omphalocele, a defective anterior abdominal wall remains as normal apposition of the rectus abdominis does not occur.
diagnosis
the primary abnormality is an anterior abdominal wall defect involving the umbilical cord. the contents may include peritoneal fluid, bowel, liver, and spleen. associated anomalies are observed in 30% of cases, predominantly cardiac. karyotypic abnormalities are found in 10-20%, especially trisomy 18. minor defects, amounting to a small herniation of the sac into the base of the umbilical cord, must be sought as these may be more likely to be associated with karyotypic abnormalities. maternal serum alpha-fetoprotein and hcg levels may be elevated in about 90% of cases with an omphalocele.
differential diagnosis
major omphaloceles may so distort the fetal trunk that appearances can be confused with body stalk anomalies, but these are associated with body distortion below the umbilicus. the pentalogy of cantrell includes omphalocele in association with abnormalities of the heart, pericardium, sternum, and diaphragm, so the presence of an omphalocoele should prompt a careful search of these areas. prune belly syndrome, due to gross bladder distension, may occasionally be difficult to differentiate especially if there is associated oligohydramnios.
sonographic features
bowel herniation through an anterior abdominal wall defect
definable sac
umbilical vessels can be traced across and then away from sac wall
contents of sac variable, ranging from those containing fluid to those incorporating liver, bowel and spleen 30% incidence of associated anomalies, especially cardiac 10-20% incidence of karyotypic abnormalities, especially trisomy 18
associated syndromes
- amniotic band/amniotic rupture
- beckwith-wiedemann
- cloacal exstrophy
- del (9p)
- elejade
- fraser
- marshall-smith
- melnick-needles (osteodysplasty)
- oeis association
- pentalogy of cantrell
- shprintzen-goldberg
- simpson-golabi-behmel
- triploidy
- trisomy 13
- trisomy 18
references
lindfors kk, mcgahan jp, walter jp fetal exomphalos and gastroschisis; pitfalls in sonographic diagnosis am j of roen 147: 797-800
morrow r, whittle mj, mcnay mb, raine pa, gibson aa, crossley j prenatal diagnosis and management of anterior abdominal wall defects in the west of scotland prenat diag 13: 111-115