A 28-year-old primigravida from Mumbai presents at 20 weeks gestation with abnormal prenatal ultrasound findings. The fetus is noted to have a large abdominal wall defect with herniation of bowel loops and liver into the amniotic sac, covered only by a thin translucent membrane. The defect is located to the right of the umbilical cord insertion. On further imaging, the herniated viscera are not covered by peritoneum. Which embryological failure is responsible for this condition?

Explanation

## Embryological Basis of Gastroschisis ### Normal Abdominal Wall Development The abdominal wall forms through the fusion of four body wall folds: 1. **Cranial fold** — forms the thoracic wall 2. **Caudal fold** — forms the lower abdominal wall 3. **Lateral folds** (right and left) — form the lateral and ventral abdominal wall These folds meet and fuse in the midline during **weeks 4–8 of gestation**, enclosing the intraperitoneal organs and forming the rectus abdominis muscles and linea alba. ### Pathophysiology of Gastroschisis **Key Point:** Gastroschisis results from failure of the lateral body wall folds to fuse completely in the midline, typically to the right of the umbilical cord insertion. This is a defect of the **somatopleure** (somatic mesoderm + ectoderm). **Clinical Pearl:** Unlike omphalocele, gastroschisis: - Has NO peritoneal covering (bare viscera exposed to amniotic fluid) - Is located **lateral to the umbilical cord** (usually right side) - Has higher rates of associated malrotation and intestinal atresia - Is NOT associated with chromosomal abnormalities (unlike omphalocele) ### Differential: Gastroschisis vs. Omphalocele | Feature | Gastroschisis | Omphalocele | |---------|---|---| | **Location** | Lateral to cord (usually right) | At cord insertion (midline) | | **Covering** | None (bare viscera) | Peritoneum + amnion | | **Associated anomalies** | Rare (malrotation, atresia) | Common (Beckwith–Wiedemann, chromosomal) | | **Embryological defect** | Lateral body wall fold failure | Failure of midgut rotation or umbilical ring closure | | **Prognosis** | Generally better if isolated | Depends on associated anomalies | **High-Yield:** The **timing** of the defect determines the phenotype: - Defect **before week 6** → omphalocele (failure of umbilical ring closure) - Defect **weeks 6–10** → gastroschisis (failure of lateral fold fusion) ## Why This Answer Is Correct The clinical presentation of a defect **to the right of the umbilical cord** with **bare viscera and no peritoneal covering** is pathognomonic for gastroschisis, which results from incomplete fusion of the lateral body wall folds during weeks 4–8.