A 3-year-old boy presents with recurrent episodes of bilious vomiting and abdominal pain. Imaging reveals the duodenojejunal flexure positioned to the right of the midline and a midline cecum. Which embryological error best explains the abnormal position of the duodenojejunal flexure compared to the normal position of the ligament of Treitz?

Explanation

## Embryological Basis of Malrotation ### Normal Gut Rotation Sequence During weeks 6–10: 1. Midgut herniates through the umbilicus 2. **270° counterclockwise rotation** around the SMA axis occurs 3. Duodenojejunal flexure rotates **left of the midline** 4. Ligament of Treitz **fixes** this flexure in place 5. Cecum rotates to the **right lower quadrant** ### Incomplete Rotation Pathophysiology ```mermaid flowchart TD A["Midgut herniation<br/>weeks 6-10"]:::outcome --> B{"Rotation around SMA?"}:::decision B -->|"Normal: 270° CCW"| C["Duodenojejunal flexure<br/>LEFT of midline"]:::outcome C --> D["Ligament of Treitz<br/>FIXES flexure"]:::action D --> E["Stable anatomy<br/>No volvulus risk"]:::outcome B -->|"Incomplete: < 270° CCW"| F["Duodenojejunal flexure<br/>RIGHT/MIDLINE"]:::outcome F --> G["Ligament of Treitz<br/>FAILS to fix"]:::urgent G --> H["Unfixed mesentery<br/>VOLVULUS risk"]:::urgent ``` ### Key Point **Incomplete rotation** means the midgut rotates less than the normal 270° counterclockwise around the SMA. The duodenojejunal flexure therefore fails to reach the left side of the midline and does not become fixed by the ligament of Treitz. This leaves the mesentery wide and mobile, predisposing to midgut volvulus. ### Clinical Pearl The clinical presentation (bilious vomiting, recurrent pain) in this 3-year-old is classic for **malrotation with intermittent volvulus**. The imaging findings (right-positioned duodenojejunal flexure, midline cecum) confirm incomplete rotation. Ladd's procedure restores the normal anatomy by positioning the duodenojejunal flexure left of the midline. **High-Yield:** Incomplete rotation is the most common form of midgut malrotation and is the embryological basis of symptomatic malrotation in children.