## Congenital Abdominal Wall Defects on Obstetric USG **Key Point:** Omphalocele is the most common congenital abdominal wall defect detected on prenatal ultrasound, occurring in approximately 1 in 4,500 live births. ### Distinguishing Features on Ultrasound | Feature | Omphalocele | Gastroschisis | |---------|-------------|---------------| | **Location** | Midline, at umbilicus | Paraumbilical (usually right) | | **Contents** | Bowel, liver, other organs | Bowel only (no liver) | | **Covering** | Membranous sac present | No covering membrane | | **Associated anomalies** | Frequent (Beckwith-Wiedemann, trisomy 13/18) | Rare | | **Amniotic fluid** | Normal | Often polyhydramnios | | **Prognosis** | Better with liver involvement | Generally good | **High-Yield:** Omphalocele containing liver (macro-omphalocele) is strongly associated with Beckwith-Wiedemann syndrome and requires postnatal screening for Wilms tumour and hypoglycaemia. ### Ultrasound Appearance - Cystic or mixed echogenic mass at umbilicus - Peristaltic movements within the sac (bowel loops) - Echogenic content if liver is present - Thin hyperechoic membrane surrounding the defect **Clinical Pearl:** Gastroschisis, though less common overall, has a worse in-utero prognosis (higher miscarriage rate) but better postnatal outcomes after surgical repair, whereas omphalocele has better in-utero survival but is associated with chromosomal abnormalities. **Mnemonic: OMPHALOCELE** - **O**mbilicus — midline location - **M**embrane — covered by sac - **P**ossible — liver involvement - **H**igh — association with syndromes - **A**ssociated — anomalies common - **L**arge — can be macro (>5 cm) - **O**rgan — multiple organs inside - **C**overing — protective membrane present - **E**cho — mixed echogenicity - **L**eft/Right — midline only - **E**arly — detected at 18–22 weeks
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