Gastroskisis

01Pathophysiology

Gastroschisis results from a full-thickness defect of the anterior abdominal wall, located to the right of a normally inserted umbilical cord. The prevailing theory attributes this to premature involution or disruption of the right umbilical vein, which weakens the paraumbilical mesenchyme during the critical window of abdominal wall closure (weeks 5-8 of gestation). An alternative hypothesis points to abnormal involution of the omphalomesenteric (vitelline) artery, resulting in focal ischemia of the body wall.

The key distinction from omphalocele is the absence of a peritoneal membrane. Because the herniated bowel is directly exposed to amniotic fluid throughout gestation, a chemical peritonitis develops. Prolonged exposure causes the bowel wall to become thickened, edematous, and matted with a fibrinous peel. This is why neonates with gastroschisis frequently develop dysmotility and feeding intolerance postnatally, even after successful surgical closure. The degree of bowel damage correlates with the duration and severity of amniotic fluid exposure.

The association with young maternal age is strong and consistent across populations, distinguishing it epidemiologically from omphalocele, which is associated with older maternal age and chromosomal anomalies. Gastroschisis itself carries a very low rate of associated chromosomal abnormalities, and the primary morbidity relates to the bowel itself (atresia, stenosis, volvulus, or necrotizing enterocolitis) rather than syndromic features.

"Closing" or "vanishing" gastroschisis is a feared complication where the abdominal wall defect narrows in utero, constricting the herniated bowel and its mesenteric blood supply. This can lead to bowel ischemia, necrosis, and atresia, and is an indication for urgent delivery consideration.

02Classification and Clinical Manifestation

03Radiologic Anatomy and Pathophysiology

On prenatal ultrasound, gastroschisis is identified by the presence of bowel loops herniated through the abdominal wall and floating freely in amniotic fluid. The defect is characteristically located to the right of the umbilical cord insertion, which itself inserts normally into the abdominal wall. This is a critical discriminating feature from omphalocele, where the cord inserts directly into the hernia sac.

The reason the bowel appears to "float" is the absence of any peritoneal or amniotic membrane. In early gestation, the loops are thin-walled and move freely. As pregnancy progresses, prolonged amniotic fluid exposure induces a fibrinous chemical peritonitis that causes the loops to become matted and thickened, sometimes referred to as the "cauliflower sign" on ultrasound. This progressive bowel wall thickening and dilation on serial scans is monitored closely because it may indicate worsening bowel damage.

On postnatal imaging (if required), an abdominal radiograph may show a paucity of bowel gas in the abdomen with gas-filled loops visible outside the body wall. After surgical closure, serial radiographs are obtained to monitor for bowel obstruction, ileus, or evidence of necrotizing enterocolitis. The bowel often takes weeks to regain normal motility.

Multi-Modality Appearance

Prenatal Ultrasound

• Free-floating loops of bowel in amniotic fluid without a covering membrane.

• Abdominal wall defect typically 2-4 cm, right paraumbilical.

• Normal umbilical cord insertion, separate from the defect.

• Bowel wall thickening (> 3 mm) and dilation (> 17-18 mm intra-abdominal or > 11-12 mm extra-abdominal) are signs of worsening condition.

• Polyhydramnios or oligohydramnios may develop; stomach and liver remain intra-abdominal.

• Serial growth scans for IUGR, which is common.

Prenatal MRI (when performed)

• Useful in late third trimester when ultrasound views are limited.

• T2-weighted sequences show high-signal amniotic fluid surrounding herniated low-to-intermediate signal bowel loops.

• Can better delineate matted vs. free bowel, and assess for associated bowel atresia (marked dilation of a proximal segment with abrupt caliber change).

Postnatal Radiograph

• Typically a clinical diagnosis at birth, so imaging is adjunctive.

• Gasless or near-gasless abdomen in the first hours of life.

• Post-reduction films used to assess bowel gas pattern for evidence of obstruction or perforation.

Postnatal Ultrasound

• May be used to assess intra-abdominal pressure after closure and evaluate for renal anomalies (associated in a small percentage).

04Diagnostic Workup

The workup begins with the elevated MSAFP on routine second-trimester screening, which triggers a targeted ultrasound. MSAFP is elevated because the exposed bowel mucosa, lacking any membrane cover, allows alpha-fetoprotein to leak freely into the amniotic fluid and then into the maternal circulation. This is why MSAFP levels in gastroschisis tend to be higher than in omphalocele, where the intact membrane limits AFP leakage.

On ultrasound, the diagnosis is usually straightforward when the classic triad is present: bowel outside the abdomen, no membrane, and a defect to the right of the cord. Amniocentesis for karyotyping is generally considered optional in isolated gastroschisis because the association with chromosomal anomalies is very low (< 1%), unlike omphalocele where trisomy 13, 18, and Beckwith-Wiedemann syndrome must be excluded.

Serial ultrasound monitoring focuses on bowel dilation, wall thickening, and fetal growth restriction, all of which guide delivery timing. Most centers plan delivery at 37-38 weeks, though earlier delivery may be indicated if there is concern for closing gastroschisis or progressive bowel compromise.

05Management and Treatment

The initial management principle is to minimize ongoing bowel injury and fluid/heat loss. The bowel bag (lower-body silo bag) reduces evaporative losses and prevents desiccation. The infant is positioned carefully to avoid kinking the mesentery.

Primary closure is preferred when feasible, as it shortens hospital stay and time to full feeds. However, this requires adequate abdominal domain. Intravesical or intragastric pressure monitoring can guide whether primary closure is safe (pressures > 20 mmHg suggest excessive tension and risk of abdominal compartment syndrome). If primary closure is not safe, a preformed spring-loaded silo is applied at the bedside (often in the NICU without general anesthesia), and the bowel is reduced by gravity and gentle pressure over several days.

Feeding intolerance is the hallmark postoperative challenge. The chemical peritonitis and bowel wall injury from amniotic fluid exposure cause prolonged ileus, sometimes lasting weeks. TPN-associated cholestasis is a significant concern in infants requiring prolonged parenteral nutrition. Complex gastroschisis with atresia may require bowel resection and carries risk of short bowel syndrome.

06Differential Diagnosis and Distractors