Axial CECT of abdomen showing altered relation of SMA and SMV. The duodenal flexure is seen on the right of midline(not shown here). |
volume rendered images of bowel showed transverse orientation of ascending colon with caecum and appendix in right upper quadrant. |
VR images of major vessels showed SMA to the right of SMV. |
·
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.
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