MRI of the fetal gastrointestinal tract

To determine the MRI patterns of the gastrointestinal (GI) tract in normal fetuses and some GI tract abnormalities.

A retrospective (1996-1998) and prospective (1999-2000) study of 48 fetal abdominal MRI scans was performed between 23 and 38 weeks of gestation. T1-weighted (T1-W) fast gradient-echo (Flash 2D) and T2-weighted (T2-W) HASTE sequences were obtained on a 1.5-T unit, in frontal and sagittal planes, after maternal premedication. Fresh meconium was also studied.

Normal patterns (40 cases): the rectum was seen in all cases and exhibited meconium-like high signal on T1-W images and low signal on T2-W images. It was close to the bladder whatever the fetal gender with its cul-de-sac being at least 10 mm below the bladder neck. The large bowel had a same signal; the distal colon was demonstrated more frequently than the proximal colon. The small bowel was transiently hyperintense on TI-W images early in gestation and then hyperintense on T2-W images. Normal measurements were obtained. GI tract abnormalities (eight cases): cysts close to normal bowel ( n=2), atresias ( n=5; microcolon, dilated small bowel with abnormal signal, one with a meconium cyst) and a cloacal malformation with midgut malrotation ( n=1; abnormal liquid signal in the rectum separated from the bladder wall and colon located on the left side).

MRI provided complete visualisation of the fetal GI tract, showed specific signal intensities, identified the level of an obstruction, detected a microcolon, and demonstrated communication between urinary and GI tracts. It shows great potential.