Echogenic fetal bowel
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% in second trimester fetuses.
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 haemorrhage, which is subsequently swallowed by the fetus.
It may be most commonly seen in the right lower quadrant of the fetus.
Echogenic bowel can be a normal variant / isolated finding in up to ~70% of cases 6,12.
Recognised associations include:
intra-amniotic haemorrhage: with subsequent swallowing of blood products
- this is considered one of the commonest causes of echogenic fetal bowel, and it may occur after an 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 IUFD 6
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, although this is not commonly used in clinical practice.
- grade 0: isoechoic to liver
- grade 1: mildly hyperechoic to liver or less than bone
- grade 2: moderately hyperechoic compared to liver or as echogenic as bone
- grade 3: markedly hyperechoic compared to 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
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 counselling, 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
Ultrasound - obstetric
- ultrasound (introduction)
- obstetric ultrasound
first trimester and early pregnancy
- gestational sac
- yolk sac
- Beta-hCG levels
- ectopic pregnancy
- multiple gestations
- subchorionic hematoma
- failed early pregnancy
- fetal biometry
- fetal morphology assessment
- fetal echocardiography views
- nonvisualisation of the fetal stomach
- nuchal fold thickness
- absent nasal bone
- choroid plexus cysts
- enlarged cisterna magna
- shortened fetal long bones
- echogenic intracardiac focus (EIF)
- echogenic fetal bowel
- aberrant right sublavian artery
- fetal pyelectasis / fetal renal pelvic dilatation
- single umbilical artery
- sandal gap toes
- umbilical artery Doppler assessment
- fetal middle cerebral arterial Doppler assessment
- nuchal translucency
- chorionic villus sampling (CVS) and amniocentesis
- first trimester and early pregnancy
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