Echogenic fetal bowel
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Echogenic fetal bowel is an observation in antenatal ultrasound imaging, in which fetal bowel appears to be brighter than it is supposed to be. It is a soft marker for trisomy 21 and has several other associations. When observed, it needs to be interpreted in the context of other associated abnormalities.
The estimated incidence is reported to range from 0.2-1.8% of 2nd trimester fetuses.
Echogenic bowel can be a normal variant/isolated finding in up to ~70% of cases 6,12.
Recognized associations include:
intra-amniotic hemorrhage: with subsequent swallowing of blood products
this is considered one of the commonest causes of an echogenic fetal bowel, and it may occur after amniocentesis or placental abruption
trisomy 21 (~15%) 12
intrauterine cytomegalovirus infection: (~15%) 5,12
detects 2-11% of cystic fibrosis cases 11,12
may have a higher association if there is concurrent bowel dilatation
intrauterine growth restriction (IUGR): (~5%) 12
intrauterine fetal demise (IUFD): ~9x increased risk
particularly if serum alpha-fetoprotein levels are also elevated 7
some data suggests that echogenic bowel occurs before 30 weeks when there is subsequent intrauterine fetal demise 6
The cause of echogenic fetal bowel is uncertain, although it has been postulated that it is related to loss of water from meconium. Note that meconium can become echogenic in the third trimester. It may also be caused by intra-amniotic hemorrhage, which is subsequently swallowed by the fetus.
It is most commonly seen in the right lower quadrant of the fetus.
To be truly "echogenic bowel" it must be brighter than bone (e.g. femur, spine), and this should be demonstrated on an image with appropriate gain settings. Tissue harmonic imaging and compound imaging should also be switched off.
A sonographic grading system exists to assess the degree of echogenicity 15, although this is not commonly used in clinical practice.
grade 0: isoechoic to liver
grade 1: mildly hyperechoic to the liver or less than bone
grade 2: moderately hyperechoic compared to the liver or as echogenic as bone
grade 3: markedly hyperechoic compared to the liver or greater than bone
If there is difficulty discerning whether bowel is as echogenic as bone, one can progressively decrease the image gain to see which structure disappears first.
Treatment and prognosis
An isolated echogenic bowel is associated with a normal outcome in 75% of cases.
Workup of this finding should include, where available, an ultrasound study to assess for any associated anomalies, referral to genetic counseling, TORCH serology, cystic fibrosis carrier testing, and offer of amniocentesis.
Imaging differential considerations include:
falsely increased bowel echogenicity due to a high transducer frequency (especially when 8 MHz is used instead of 5 MHz 4)
in the 3rd trimester, meconium-containing bowel may appear echogenic as a normal finding 10
meconium peritonitis: coarse calcifications, pseudocysts
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