What is malrotation of the small bowel?

Malrotation of the Small Bowel

Malrotation of the small bowel is a congenital anomaly resulting from abnormal rotation and fixation of the intestine during fetal development, which can lead to life-threatening midgut volvulus requiring emergency surgical intervention.

Definition and Embryology

Malrotation occurs when there is a disruption in the normal embryological development of the bowel, resulting in:

• Abnormal position of the duodenojejunal junction (normally lateral to the left-sided pedicles of the vertebral body)
• Abnormal location of the cecum and ascending colon (often in the mid-abdomen or left side)
• Narrow mesenteric base that predisposes to volvulus (twisting of the intestine)
• Presence of abnormal peritoneal bands (Ladd's bands) that can cause duodenal obstruction

Clinical Presentation

Malrotation can present at various ages, though most commonly in infancy:

• Neonates/Infants: Bilious vomiting (most common and concerning symptom), abdominal distension
• Children/Adolescents: Intermittent vomiting, chronic abdominal pain, failure to thrive
• Adults: Often asymptomatic or with vague abdominal complaints

The most concerning complication is midgut volvulus, which can lead to:

• Intestinal ischemia
• Bowel necrosis
• Sepsis
• Death if not promptly treated

Diagnosis

The gold standard for diagnosis is the upper gastrointestinal (UGI) series 1:

• Shows abnormal position of the duodenojejunal junction
• Has sensitivity of approximately 96% 1
• May demonstrate the "corkscrew" appearance of the duodenum in volvulus

Potential diagnostic pitfalls with UGI series include:

• False positives (10-15%) due to redundant duodenum, bowel distension, or improper technique 1, 2
• False negatives (rare but reported) where normal jejunal position is seen despite malrotation 1

Ultrasound findings may include:

• Abnormal superior mesenteric vein (SMV) position relative to superior mesenteric artery (SMA)
• "Whirlpool sign" - clockwise wrapping of SMV and mesentery around SMA (highly specific for volvulus) 1
• Limited by bowel gas obscuration in up to 17% of cases 1

CT scan may show:

• Abnormal position of duodenojejunal junction and cecum
• Whirlpool sign in cases of volvulus
• Associated complications such as intestinal obstruction

Management

Surgical intervention is required for symptomatic malrotation, particularly with volvulus:

1. Ladd Procedure - the standard surgical treatment 3, 4:

   • Evisceration and inspection of the mesenteric root
   • Counterclockwise derotation of midgut volvulus (if present)
   • Lysis of Ladd's bands with straightening of the duodenum
   • Appendectomy (due to abnormal position of appendix)
   • Placement of the cecum into the left lower quadrant
   • Can be performed laparoscopically in stable patients 4

2. Emergency surgery is required for:

   • Patients with volvulus
   • Signs of intestinal ischemia
   • Bowel obstruction

3. Bowel resection may be necessary if:

   • Intestinal ischemia or necrosis is present
   • Strictures have developed (as can occur in recurrent volvulus) 5

Prognosis

• Excellent prognosis with early diagnosis and treatment
• Higher morbidity and mortality with delayed diagnosis, especially if intestinal ischemia develops
• Recurrent volvulus can occur even years after initial surgery 5
• Close follow-up is recommended, especially in patients with atypical presentations

Special Considerations

• Malrotation can be detected prenatally through identification of gastric malposition on ultrasound 6
• Patients with previous surgery for malrotation who present with acute bowel obstruction should be evaluated for recurrent volvulus, not just adhesions 5
• A high index of suspicion is needed in patients with vague, chronic abdominal symptoms, as malrotation can present beyond the neonatal period 4