PARTIAL MIDGUT MALROTATION

Coronal post contrast CT section through pancreas showing
absent 3rd part of duodenum beneath the pancreas.

Axial post contrast CT section through kidneys showing clumped duodenum infero medial to pancreas with antero posterior relation of superior mesenteric vessels.
 

Intestinal malrotation can be broadly defined as any deviation from the normal 270° counterclockwise rotation of the midgut during embryologic development.

· Malrotation results not only in the malposition of the bowel but also in the malfixation of the mesentery.

· The normally broad mesenteric attachment is shortened to a narrow pedicle that predisposes the patient to the complication of midgut volvulus.

· Internal hernia related to abnormal peritoneal fibrous bands (of Ladd) that attach to the right colon is another complication of malrotation seen in adults.

· Conventional radiography is neither sensitive nor specific for malrotation, although right-sided jejunal markings and the absence of a stool-filled colon in the right lower quadrant may be suggestive of this finding.

· The upper gastrointestinal barium series remains accurate for detection, and the rules familiar to pediatric radiology also apply for adults—that is, the duodenal—jejunal junction fails to cross the midline and lies below the level of the duodenal bulb.

· An abnormal junction in an adult should not be dismissed as a normal variant.

· Contrast enema examination usually shows malposition of the right colon, but the cecum may assume a normal location in up to 20% of patients.

· The contrast enema findings are also nonspecific because cecal location can be variable without malrotation.

· Many cases of quiescent malrotation in adults are currently being detected on cross-sectional imaging performed for various unrelated reasons.

· CT not only shows the intestinal malpositioning seen on barium studies but also depicts associated extraintestinal findings not evident on conventional examinations. For example, deviation from the normal relationship between the SMA and SMV is a useful indicator of malrotation.

· In most patients with quiescent malrotation, the SMA and SMV will assume a vertical relationship or show left—right inversion.

· Analogous findings can be seen on sonography.

· Abnormalities of SMA—SMV orientation are not entirely diagnostic, however, because some patients with malrotation will have a normal relationship, and a vertical or inverted relationship can also be seen in patients without malrotation.

· Therefore, isolated detection of such an abnormality is not sufficient for diagnosis but should warrant closer examination of the bowel.

· Finally, inspection of the pancreas in malrotation will reveal underdevelopment or absence of the uncinate process.

· Acute complications of malrotation:

1. Midgut volvulus

2. Internal hernia

· Regardless of patient age, surgical treatment of quiescent malrotation should be considered because surgery remains the only real safeguard against complications.

Reference : Intestinal Malrotation in Adolescents and Adults: Spectrum of Clinical and Imaging Features, AJR December 2002 vol. 179 no. 6 1429-1435.