Gastroschisis

Gastroschisis refers to extra-abdominal herniation (evisceration) of fetal or neonatal bowel loops (and occasionally portions or the stomach and or liver) into the amniotic cavity through a para-umbilical anterior abdominal wall defect.  

Epidemiology

The estimated incidence is at around 1-6 per 10,000 live births. There may be a male predilection and an increased incidence with younger maternal age. 

Pathology

This anomaly does not have a surrounding membrane (unlike an uncomplicated omphalocoele). It is the small bowel that herniates most often. The defect is invariably on the right side and usually measures between 2-4 cm. There is no covering membrane or membrane remnant.

Content

The small intestine always herniates through the abdominal wall defect and lacks normal rotation and fixation to the posterior abdominal wall. In addition to the small intestine, the large intestine, stomach, portions of the genitourinary system and liver may herniate through the defect as well. 

Aetiology

A compromise in vascular supply to the area in the abdominal wall adjacent to the umbilicus may be a causative factor. Some also suggest an incomplete regression of the right umbilical vein as a possible causative factor.

Genetics

Most cases have a sporadic occurrence.

Associations

Associated anomalies are rare in a gastroschisis (unlike an omphalocoele) except for related bowel abnormalities (i.e. intestinal atresia, malrotation or stenosis from vascular compromise).

A fetus with a gastroschisis may have intrauterine growth restriction (IUGR) ⁶.

Serological markers

• maternal serum alpha-fetoprotein (MSAFP) may be elevated: the extent of AFP rise is often greater for a gastroschisis than for an omphalocoele

Radiographic features

Antenatal ultrasound

The herniated content is towards the right side of the umbilical cord in most cases; colour Doppler may be useful to locate the cord in relation to the herniation. This causes the fetal abdominal circumference to be smaller than expected for gestation age. The herniated bowel often appears free floating rather than contained. The herniated bowel wall can be thickened due to oedema.

There can be either accompanying oligohydramnios or polyhydramnios as ancillary sonographic features.

Treatment and prognosis

There can be an intra-uterine mortality rate of 10-15%. The condition of the bowel at birth is the single most important prognostic factor. An antenatal diagnosis of gastroschisis may facilitate a planned delivery in a specialised unit (tertiary care centre) with parental counselling as well as surgical planning. Most infants are treated surgically on the first day of life. In general, it carries a good survival rate post surgery ³. Some state that the smaller the gastroschisis, the greater the risk of ischaemia to the herniated gut due to a more severe restriction of blood flow. Antenatal diagnosis of accompanying fetal bowel dilatation (especially if over 20 mm ⁸) is also considered a poorer outcome.

Complications

There are a number of complications which can mainly involve the bowel and include:

• in utero bowel obstruction
• in utero bowel perforation
• peritonitis: meconium peritonitis
• motility dysfunction
• necrotising enterocolitis
• short-gut syndrome
• fistula formation
• neonatal gastro-oesophageal reflux: especially following repair ⁴

Differential diagnosis

General imaging differential considerations include:

• omphalocoele (particularly if ruptured): is accompanied by a surrounding membrane, cord insertion is central
• physiological gut herniation: can occur in early gestation (before 11 weeks)

History and etymology

Arises from the Greek gas-tros'ki-sis - gastro (stomach) plus schisis (fissure).

See also

• fetal abdominal wall defects