Purpose or Case Report: To assess if malrotation of the bowel can be detected on prenatal MRI.
Methods & Materials: Nine cases of malrotation diagnosed postnatally by UGI in 8 cases and autopsy in 1 case had prenatal MRI imaging. Postnatal imaging (including SBFT/ KUB) was utilized to determine the position of small bowel and colon and to determine if obstruction was present. Prenatal MRIs were retrospectively reviewed to determine if bowel position matched the postnatal position. Prenatal factors documented: Gestational age, reason for MRI, AFI, small bowel and colon position, and bowel dilatation. Postnatal factors recorded include: reason for the UGI, bowel orientation and obstruction, and surgical findings. A control group of 98 prenatal MRIs was prospectively evaluated to determine if normal bowel orientation could be visualized.
Results: Prenatal MRI was performed for heterotaxy 5/9, congenital heart disease 3/9, and skeletal dysplasia 1/9. Indications for postnatal UGI included emesis 3/9, peritonitis 1/9, distended abdomen 1/9, and asymptomatic heterotaxy 4/9. Gestational age at MRI ranged from 23-37 weeks. AFI’s were normal and no cases had dilated bowel. Prospectively, malrotation was suspected in 5 cases. Retrospectively on MRI, small bowel position was best assessed on T2 coronal images; colon T1 coronal images. Small bowel was nonrotated in 9/9 cases with small bowel positioned contralateral to stomach situs. Colon was nonrotated in 7/9 cases, contralateral to the small bowel in 6/7 and on the same side as the small bowel in 1/7. Colon position was indeterminate in 1/9; not seen 1/9. Prenatal small bowel position corresponded to the UGI/SBFT or autopsy in all cases with nonrotation in 8/9; partial rotation of the duodenum in 1/9. Colon prenatal position corresponded to the SBFT/KUB or autopsy with nonrotation in 7/7 cases. Of the 2/9 with indeterminate prenatal colon position, postnatal colon was nonrotated. No postnatal cases were obstructed. Surgery confirmed diagnosis in 4/9; autopsy 1/9 cases. The prenatal MRI control group had GA ranging from 21 to 38 weeks and normal bowel rotation seen in all cases.
Conclusions: Detection of bowel malrotation on prenatal MRI is possible with careful analysis of the small bowel and colon position. In a fetus with heterotaxy, prenatal analysis of the position of the bowel is useful secondary to the increased incidence of malrotation. If malrotation is suspected prenatally, postnatal evaluation prior to onset of symptoms may minimize potential for subsequent complication.