Echogenic Bowel on Fetal Ultrasound
by Beth A. Pletcher, MD, September 1998

The finding of echogenicity within the fetal abdomen prompts a rather extensive work-up and poses a clinical diagnostic dilemma for many practitioners. The most common anatomic abnormalities associated with this sonographic finding include: meconium peritonitis with or without intestinal atresia, meconium ileus and intestinal malrotation. Ascites seen in association with echogenic foci is suggestive of a true meconium peritonitis whereas intraluminal calcifications alone are more suggestive of a simple meconium ileus. Bowel obstruction is most often associated with proximal bowel dilatation and is seen with a malrotation, atresia and some cases of meconium ileus.

In addition to anatomic variations, a number of other diagnostic concerns are raised in this clinical setting. Cytomegalovirus and other TORCH infections are not infrequently associated with these ultrasound findings as well as cystic fibrosis and cytogenetic abnormalities such as Trisomy 21. What is a reasonable approach when trying to evaluate this non-specific finding and what should we be telling these patients?

1. First of all we have come to recognize that echogenic bowel may very well be a normal anatomic variation during the second trimester. Even meconium peritonitis may spontaneously resolve and cause no problems for the newborn in the absence of an intestinal obstruction. At least 50% of fetal echogenic bowel is associated with a normal outcome at birth.

2. Serial sonograms may help to clarify the findings with special attention directed to abdominal ascites and other bowel findings such as dilatation or development of a meconium pseudocyst.

3. Earlier reports suggested a very high risk for cytogenetic problems such as Trisomy 21 in fetuses with echogenic bowel, but prospective data has failed to demonstrate as high an incidence as initially reported. Because 3% of infants with Trisomy 21 have duodenal atresia, 30% of prenatally diagnosed duodenal atresia is associated with Down syndrome and the "double bubble" sign may not become apparent until the third trimester, it is reasonable to consider amniocentesis in this clinical setting. I give a possible 5% risk for a cytogenetic problem to my patients seeking genetic counseling.

4. TORCH infections, especially CMV, have been associated with fetal ascites, hydrops and/or meconium peritonitis and should be considered in the differential diagnosis. It is reasonable to send maternal serum CMV IgG and IgM to rule out a primary infection. Because CMV has other clinical implications it is important to have this information prior to delivery. The incidence of CMV infection with fetal echogenic bowel may be as high as 15-20%.

5. Finally the issue of cystic fibrosis is raised. Because CF is frequently associated with meconium ileus at birth, this diagnostic consideration always arises when fetal echogenic bowel is noted prenatally. However, it has been our experience (as well as others) that the finding of meconium peritonitis in the second trimester is less often associated with CF. This may be because the inspissated meconium of CF develops later rather than earlier in gestation and may not be associated with the sonographic identification of intraluminal calcifications. The estimated risk for CF with this clinical finding is probably well under 10%, unless the echogenicities are noted in the third trimester or there is evidence of a meconium pseudocyst. Either of these two findings would greatly increase the chances for CF in an infant at birth. Because CF mutation screening is readily available and reasonably accurate, clinicians may decide on a case by case basis whether or not to pursue this testing. It is best done when both parents are available and may assist the pediatricians in caring for the infant at birth.