Echogenic Bowel

Echogenic bowel is an ultrasound finding in which there is increased brightness of fetal bowel, greater than or equal to that of bone. It is also referred to as hyperechoic bowel.¹

Abnormal ultrasonic finding on antenatal screening of mother O28.3

Echogenic bowel of fetus O35.8XX0

In the general obstetric population, the incidence is 0.2% - 1.4%.² It is most often identified during the second trimester anatomy ultrasound.  Echogenicity of the bowel increases with the gestational age and can be a normal finding in the third trimester due to presence of meconium in the colon.^1,3,4 

    Aneuploidy
    Intestinal anomalies such as obstruction, atresia, or perforation
    Cystic fibrosis
    Congenital infection
    Intra-amniotic bleeding
    Fetal growth restriction
 

The pathophysiology of echogenic bowel varies according to the etiology. It can range from little clinical significance to major underlying pathology.⁵     

• Aneuploidy: Bowel hypotonia and subsequent dysmotility occurs more frequently in fetuses with aneuploidy.  This leads to stasis within the intestines, increased absorption of fluid from the bowel lumen and ultimately thickened meconium, giving the appearance of echogenic bowel. This is commonly referred to as meconium ileus. When echogenic bowel is detected on a second-trimester ultrasound, there is an increased risk for Trisomy 21, and less commonly Trisomy 13 and 18, Turner’s syndrome, or triploidy, with rates ranging from 6.6-13%.^3,5–8 
• Intestinal anomalies: Bowel pathology such as duodenal atresia, jejunoileal atresia, intestinal duplication, omphalocele, and anorectal malformation can result in bowel dysfunction, obstruction or dysmotility. In these disorders, there is increased fluid absorption from the bowel resulting in thickened meconium and subsequent echogenic bowel.  Rates of occurrence can range from 1-12.5%. When echogenic bowel is associated with bowel dilation, ascites, or calcification, there is higher risk for gastrointestinal pathology that may require postnatal intervention.^3,6,9,10
• Cystic fibrosis: Cystic fibrosis is a common autosomal recessive disease, with an incidence of 1 in 3500 births and a carrier rate of 1 in 30 in the Caucasian population. Fetuses with cystic fibrosis have abnormal pancreatic enzymes that alter the secretory, digestive, and absorptive function within the small intestine, resulting in a viscous meconium.⁴ 1.5-4% of fetuses with echogenic bowel can be associated with cystic fibrosis.^3,7,8  
• Congenital infections: Congenital infections can cause fetal bowel inflammation and edema.  This can result in decreased peristalsis of infected bowel with subsequent perforation and later calcification at perforation sites.⁴ Cytomegalovirus (CMV), parvovirus B19, and toxoplasmosis are the most common infections associated with echogenic bowel, with rates ranging from 1-11%. ^3,6,7,10,11
• Intra-amniotic bleeding: Vaginal bleeding, subchorionic hematomas, and placental lakes can be associated with the presence of intra-amniotic blood.^9,11 Bleeding can also occur following invasive procedures such as chorionic villus sampling and amniocentesis.  Amniotic fluid containing blood is then swallowed by the fetus, which has an echogenic appearance.
• Fetal growth restriction: In the setting of intrauterine growth restriction, there is a redistribution of blood to vital organs (brain, heart, and adrenal glands). The resultant decrease in splanchnic blood flow causes areas of bowel hypoperfusion and ischemia.  Impaired circulation secondary to uteroplacental insufficiency is also thought to play a role in bowel hypoxia, which can affect normal bowel function and peristalsis, resulting in echogenic bowel. ^4,5,8

Echogenic bowel can be an isolated finding in 55-80% of cases.^4,8,12 When associated with aneuploidy, other congenital abnormalities may be noted, most often involving the central nervous system, the heart or the skeletal system.⁷ Additionally, other findings associated with aneuploidy may be identified, such as thickened nuchal fold, short long bones, aberrant right subclavian artery, pyelectasis, echogenic intracardiac focus, choroid plexus cyst, or absent/hypoplastic nasal bone.⁷   

The presence of bowel dilation can be associated with small bowel atresia or other bowel abnormalities, which typically are identified in the third trimester.^3,6,9,10 Fetuses affected by congenital CMV may also have intracranial or intra-abdominal calcifications, hepatomegaly, and/or ventriculomegaly.¹²
 

Diagnosis is made when the echogenicity of bowel is comparable to or greater than that of adjacent bone (often the iliac crest.) The severity of echogenic bowel is sometimes stratified from grade 0 to grade 3. Grade 0 is normal bowel which is of similar echogenicity to liver, Grade 1 is mildly hyperechoic compared to liver but less than bone, Grade 2 is moderately hyperechoic compared to liver or as echogenic as bone, and Grade 3 is markedly hyperechoic compared to liver or greater than bone.¹³ Grades 2 and 3 are most often associated with increased risk for adverse pregnancy outcomes, corresponding to the diagnosis of echogenicity equal to or greater than that of bone.¹⁴ 
 

False positive diagnoses of echogenic bowel can occur when a high-frequency probe is used, such as the 8 MHz, which increases the subjective echogenicity of bowel. Therefore the diagnosis should be confirmed using a low-frequency probe (<5MHz.)^1,15 The diagnosis should not be made on transvaginal ultrasound. Additionally, when echogenic bowel is suspected, the gain should be decreased until only bowel and bone remain in the image, and the bowel imaged in both sagittal and transverse planes. Image enhancement systems and tissue harmonics should be inactivated. Though there have been attempts to standardize the diagnosis, interobserver variability does exist.^15,16 Care should be taken not to over call echogenic bowel after a new ultrasound machine is purchased. 

Echogenic bowel can be seen in several different conditions. Therefore, when found during routine ultrasound screening, it should prompt further evaluation for associated abnormalities and the underlying etiology.¹² If fetal echogenic bowel is an isolated sonographic finding, the risk is lower for aneuploidy (1.4% - 6.7%) compared to echogenic bowel with other major anomalies (up to 17.4%.)^7,12 Echogenic bowel found with additional anatomic anomalies has been associated with a 4.9-fold increase for CMV or toxoplasmosis, 10.8-fold increase for cystic fibrosis or other genetic disorders, 4.1-fold increase for IUGR and a 6.8-fold increase for other significant conditions.¹⁷

The prognosis when echogenic bowel is identified depends on the underlying cause, the timing of diagnosis, and the presence or absence of associated abnormalities.  When diagnosed late in pregnancy, the bowel may appear more echogenic due to the physiologic increase in meconium content in the bowel, lending a more favorable prognosis.¹² The prognosis in cases of congenital CMV or other congenital infections is dependent on the timing of infection and the severity of associated abnormalities. Similarly, the prognosis in pregnancies complicated by aneuploidy is related to the specific chromosome abnormality.  When associated with dilated bowel that persists until delivery, approximately 53% of fetuses will have a bowel abnormality diagnosed after birth.¹⁸

Up to 50% of echogenic bowel will resolve antenatally¹⁸ and improvement or stabilization of echogenic bowel has been associated with an 8.1-fold increased chance on normal neonatal outcome.¹²

A number of studies have also reported an association between echogenic bowel and adverse pregnancy outcomes such as intrauterine growth restriction (5.2-21%) and intrauterine fetal demise (3.2-9.5%.)^{3,5,8,9,11,12,17} Goetzinger et al. found that even in isolated cases of echogenic bowel (excluding cases of aneuploidy, congenital CMV and major anomalies), the incidence of fetal growth restriction was 19.7% and the incidence of fetal demise was 5.3%. This translates into a 2.1-fold increase odds of intrauterine fetal growth restriction and a 7.4-fold increase of fetal demise. The same study reports that the incidence of fetal demise was the highest in the setting of both echogenic bowel and fetal growth restriction.⁸ 
 

When echogenic bowel is suspected on second trimester ultrasound, subsequent management includes a thorough assessment for the underlying cause. Suggestions for evaluation include:

1. Detailed anatomic survey to assess for other structural abnormalities or other sonographic markers of aneuploidy.  
2. Obtain maternal history with special attention to any history of bleeding or past invasive procedures.
3. Offer Genetic counseling. Consider  amniocentesis for karyotype, microarray and viral PCR or cell-free fetal DNA testing. 
4. Offer parental screening for cystic fibrosis.
5. Offer maternal serology for viral infections if amniocentesis is not planned.
6. Follow-up serial growth ultrasounds. This also allows for continued reassessment of the fetal bowel. If fetal growth restriction is found, Doppler interrogation and antenatal testing is recommended. Some studies suggest antenatal testing even in the absence of fetal growth restriction due to the increased risk of fetal demise^{17, 4}

1. Melamed N, Kennedy A, Glanc P. The Fetal Gastrointestinal Tract and Abdominal Wall. Fifth Edit. Diagnostic Ultrasound. Elsevier Inc.; 2017. 1304-1335 p. 
2. Hurt L, Wright M, Brook F, Thomas S, Dunstan F, Fone D, et al. The Welsh study of mothers and babies: Protocol for a population-based cohort study to investigate the clinical significance of defined ultrasound findings of uncertain significance. BMC Pregnancy Childbirth. 2014;14(1):1–7. 
3. Catania VD, Taddei A, Pellegrino M, De Marco EA, Merli L, Manzoni C, et al. Hyperechogenic Bowel: Etiologies, Management, and Outcome according to Gestational Age at Diagnosis in 279 Consecutive Cases in a Single Center. Eur J Pediatr Surg. 2017;27(1):109–15. 
4. Ebrashy A, Kurjak A, Adra A, Aliyu LD, Wataganara T, De Sá RAM, et al. Controversial ultrasound findings in mid trimester pregnancy. Evidence based approach. J Perinat Med. 2016;44(2):131–7. 
5. Buiter HD, Holswilder-Olde Scholtenhuis MAG, Bouman K, van Baren R, Bilardo CM, Bos AF. Outcome of infants presenting with echogenic bowel in the second trimester of pregnancy. Arch Dis Child Fetal Neonatal Ed. 2013;98(3):256–9. 
6. Kesrouani AK, Guibourdenche J, Muller F, Denamur E, Vuillard E, Garel C, et al. Etiology and Outcome of Fetal Echogenic Bowel. Fetal Diagn Ther. 2003;18(4):240–6. 
7. Ekin A, Gezer C, Taner CE, Ozeren M. The effect of associated structural malformations in the prediction of chromosomal abnormality risk of fetuses with echogenic bowel. J Matern Neonatal Med. 2016 Jan 2;29(1):41–5. 
8. Goetzinger KR, Cahill AG, Macones GA, Odibo AO. Echogenic Bowel on Second-Trimester Ultrasonography. Obstet Gynecol. 2011 Jun;117(6):1341–8. 
9. Saha E, Mullins EWS, Paramasivam G, Kumar S, Lakasing L. Perinatal outcomes of fetal echogenic bowel. Prenat Diagn. 2012;32(8):758–64. 
10. Scotet V, Duguépéroux I, Audrézet MP, Audebert-Bellanger S, Muller M, Blayau M, et al. Focus on cystic fibrosis and other disorders evidenced in fetuses with sonographic finding of echogenic bowel: 16-year report from Brittany, France. Am J Obstet Gynecol. 2010;203(6):592.e1-592.e6. 
11. Ameratunga DM, Said JM, Reidy K, Palma-Dias R. Perinatal outcomes following the ultrasound diagnosis of echogenic bowel: An Australian perspective. Fetal Diagn Ther. 2012;31(3):179–84. 
12. Ronin C, Mace P, Stenard F, Loundou A, Capelle M, Mortier I, et al. Antenatal prognostic factor of fetal echogenic bowel. Eur J Obstet Gynecol Reprod Biol. 2017;212(2017):166–70. 
13. Slotnick RN, Abuhamad AZ. Prognostic implications of fetal echogenic bowel. Lancet. 1996;347(8994):85–7. 
14. Strocker AM, Snijders RJ, Carlson DE, Greene N, Gregory KD, Walla CA, et al. Fetal echogenic bowel: Parameters to be considered in differential diagnosis. Ultrasound Obstet Gynecol. 2000;16(6):519–23. 
15. Harrison KL, Martinez D, Mason G. The subjective assessment of echogenic fetal bowel. Ultrasound Obstet Gynecol. 2000;16(6):524–9. 
16. Faden MS, Brown RN. Hyperechogenic Fetal Bowel in the Era of Modern Ultrasound Equipment: It Is Not Only a Matter of Gain! J Obstet Gynaecol Canada. 2018;1–3. 
17. Findley R, Allen VM, Brock JAK. Adverse Perinatal Conditions Associated With Prenatally Detected Fetal Echogenic Bowel in Nova Scotia. J Obstet Gynaecol Canada. 2018;40(5):555–60. 
18. Ruiz MJ, Thatch KA, Fisher JC, Simpson LL, Cowles RA. Neonatal outcomes associated with intestinal abnormalities diagnosed by fetal ultrasound. Vol. 44, Journal of Pediatric Surgery. 2009. p. 71–5. 

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