A 24-year-old primigravida from Delhi presents to the antenatal clinic at 16 weeks of gestation (by last menstrual period). Transabdominal ultrasound is performed for routine anomaly screening. The sonographer notes a midline defect in the anterior abdominal wall with herniation of bowel loops and liver into the amniotic sac, with no covering membrane. The defect measures approximately 5 cm. What is the most likely diagnosis?

Explanation

## Diagnosis: Gastroschisis **Key Point:** Gastroschisis is a full-thickness defect of the anterior abdominal wall, typically located to the right of the umbilicus, with evisceration of bowel (and sometimes liver) into the amniotic sac without a covering membrane. ### Ultrasound Features of Gastroschisis | Feature | Gastroschisis | Omphalocele | |---------|---------------|-------------| | **Location** | Right of umbilicus (90%) | At umbilicus | | **Covering** | No membrane | Covered by peritoneum + amnion | | **Contents** | Bowel loops, rarely liver | Bowel, liver, spleen | | **Size** | Usually < 5 cm | Variable, often > 5 cm | | **Associated anomalies** | Rare (5–10%) | Common (50–70%, e.g., trisomy 13/18) | | **Prognosis** | Good with repair | Depends on associated anomalies | **High-Yield:** Gastroschisis is a **defect in the linea alba**, not at the umbilical ring. The bowel herniates freely into amniotic fluid and may become matted, foreshortened, or dilated in utero. ### Clinical Pearl **Timing:** Gastroschisis typically presents on second-trimester anomaly scan (16–20 weeks). The defect is often visible as free-floating bowel loops adjacent to the fetal abdomen. ### Mnemonic: GASTROSCHISIS vs OMPHALOCELE **GASTRO** = **G**ap in the linea alba, **A**bsent membrane, **S**mall defect, **T**o the right, **R**are associations, **O**pen bowel loops **OMPHALO** = **O**n the umbilicus, **M**embrane-covered, **P**rominent defect, **H**igh anomaly rate, **A**ssociated syndromes, **L**arge often, **O**rgan-rich contents ### Why This Case Fits Gastroschisis 1. **Location:** Midline but described as anterior abdominal wall (right-sided defect is classic). 2. **No covering membrane:** Free evisceration into amniotic sac. 3. **Size < 5 cm:** Typical for gastroschisis; omphaloceles are often larger. 4. **Bowel + liver herniation:** Both can occur, but the absence of a covering membrane is diagnostic. [cite:Callen's Ultrasonography in Obstetrics and Gynecology 6e Ch 18]