Prenatal magnetic resonance and ultrasonographic findings in small-bowel obstruction: imaging clues and postnatal outcomes.

BACKGROUND

Prenatal small-bowel obstruction can result from single or multiple atresias, and it can be an isolated abnormality or part of a syndrome. It is sometimes the first manifestation of cystic fibrosis. Accurate prediction of the level of obstruction and length of bowel affected can be difficult, presenting a challenge for counseling families and planning perinatal management.

OBJECTIVE

To review the prenatal US and MRI findings of small-bowel obstruction and to assess whether fetal MRI adds information that could improve prenatal counseling and perinatal management.

MATERIALS AND METHODS

We retrospectively reviewed 12 prenatally diagnosed cases of small-bowel obstruction evaluated by both US and MRI from 2005 to 2015. We analyzed gestational age at evaluation, US and MRI findings, gestational age at delivery and postnatal outcomes.

RESULTS

The final diagnoses were jejunal atresia (7), ileal atresia (1), cystic fibrosis (3) and combined jejunal and anal atresia (1). Four of the eight with jejunal atresia were found to have multiple small-bowel atresias. Prenatal perforation was noted in three. We identified a trend of increasing complexity of bowel contents corresponding to progressively distal level of obstruction, as indicated by increasing US echogenicity and high T1 signal on MRI. Seven cases of jejunal atresia and one case of ileal atresia demonstrated small ascending, transverse and descending colon (microcolon) with filling of a normal-diameter rectum. In contrast, all three fetuses with cystic fibrosis and the fetus with jejunal-anal atresia demonstrated microcolon as well as abnormal paucity or absence of rectal meconium. Polyhydramnios was present in nine. Eight were delivered prematurely, of whom seven had polyhydramnios. The fetus with jejunal and anal atresia died in utero. Postnatally, three had short gut syndrome, all resulting from multiple jejunal atresias; these three were among a subset of four fetuses whose bowel diameter measured more than 3 cm. Eight infants had no further gastrointestinal complications. The presence of multiple atresias was not predicted by prenatal US or MRI.

CONCLUSION

MR provides useful additional information regarding meconium distribution in the small bowel, which helps to clarify the level of obstruction. MR was additionally useful in the assessment of colon and rectal contents, serving as a fetal enema. Abnormally diminished meconium in the rectum suggests cystic fibrosis or combined small-bowel and colonic obstruction, information that is useful in counseling and preparing for postnatal care.