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Intestinal malrotation

Intestinal malrotation is a congenital anatomical anomaly which results from an abnormal rotation of the gut as it returns to the abdominal cavity during embryogenesis.

Although some individuals live their entire life with malrotated bowel without symptoms, the abnormality does predispose to midgut volvulus and internal hernias, with the potential for life threatening complications. 

Epidemiology

Intestinal malrotation is a congenital abnormality seen in up to 1:6000 live births 5. It is also frequently (~ 50%) associated with other abdominal anomalies, some of which are causative and others merely associated 5

Clinical presentation

The clinical presentation of malrotation often correlates to the age of presentation 5.

In the infant the most common presentation is with a midgut volvulus. Patient with intestinal nonrotation have a lower incidence of midgut volvulus than other types of malrotation.

In the older child or even adult presentation is more frequently intermittent with episodes of spontaneously resolving duodenal obstruction. This is thought to be due to kinking of the duodenum by Ladd bands rather than a volvulus 5. Internal hernias are also encountered. 

In some individuals, presentation is very non-specific with episodes of abdominal pain, weight loss, melaena, or even chronic pancreatitis 5.

Pathology

During normal embryogenesis the bowel herniates into the base of the umbilical cord and rapidly elongates. As it returns to the abdominal cavity it undergoes complex ~270 degree counter clockwise rotation resulting in the duodeno-jejunal (D-J) flexure normally located to the left of the midline, at the level of L1 verterbal body and the terminal ileum located in the right iliac fossa. This results in a broad mesentery running obliquely down from the DJ flexure to the caecum, and prevents rotation around the superior mesenteric artery (SMA) 1-6.

In malrotation this does not occur and as a result the mesentery has a short root, which allows it to act as a pedicle (through which the SMA and SMV pass) around which volvulus can occur. 

Intestinal nonrotation is a subtype of malrotation in which the small bowel is mainly located in the right hemiabdomen and the caecum in the left hemiabdomen.

Radiographic features

Plain film

Abdominal radiographs, in the absence of midgut volvulus, are neither specific nor sensitive 2. They may show:

  • right sided jejunal markings
  • absence of stool filled colon in right lower quadrant
Ultrasound 

May show and inversion in the SMA/SMV relationship with the SMA on the right and the SMV on the left.

CT
  • may again show abnormal SMA (smaller and more circular)/SMV relationship
  • large bowel predominantly on left and small bowel predominantly on the right 
Fluoroscopy 

A paediatric upper gastrointestinal contrast study is the examination of choice when the diagnosis is suspected. The key findings of malrotation is an abnormal duodeno-jejunal (DJ) junction location:

  • frontal view
    • DJ junction fails to cross the midline to the left of the left-sided vertebral body pedicle
    • DJ junction lies inferior to the duodenal bulb
  • lateral view
    • second and third duodenum not located posteriorly in a retroperitoneal position

Although not a specific criteria of malrotation, the jejunum is normally located to the left of the spine.

Contrast enema has historically also been used, the theory being that in malrotation the large bowel will also be malrotated. Unfortunately in ~25% (range 20-30%) of cases with malrotation the caecum is normally located. The converse is also true, with position of the caecum in normal individuals being variable 4. Very rarely, the caecum may be malrotated and the small bowel in a normal position.

Treatment and prognosis

Due to the potential for life-threatening midgut volvulus and ischaemic bowel, once discovered malrotation is corrected surgically. The general principles of treatment are:

  • mobilisation of the bowel including untwisting any volvulus present
  • division of abnormal peritoneal bands (Ladd bands
  • widening of the mesenteric base
  • fixation of the duodenum and caecum to the retroperitoneum (pexy) is not universally performed 5-6

It should be noted that normal anatomical positioning is not achieved; the duodenum and small bowel remain on the right, and the caecum and colon are on the left side of the abdomen 5-6

Differential diagnosis

A rate of 15% false positive has been reported in the diagnosis of malrotation using barium meal 7. Hence, differential diagnoses must be kept in mind, including:

  • normal duodenum: located inferiorly because of gastric distension or abnormally because of feeding tube, renal agenesis, splenomegaly, etc.
  • duodenum inversum
  • wandering duodenum

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