|Echogenic bowel (arrows) is seen in the lower fetal abdomen & pelvis|
|2nd Trimester fetus with normal bowel echogenicity (3.5 mHz)||Same fetus scanned at 8 mHz now demonstrates bright bowel|
For several years it was assumed that this increased echogenicity was a normal variant which was likely bowel related and in most cases would disappear by the third trimester. Subsequently reports appeared in the medical literature noting an association of hyperechogenic bowel with a variety of conditions including: cystic fibrosis, karyotypic abnormalities, fetal growth retardation and fetal death. These associations with hyperechogenic bowel will be discussed below.
Ever since the early reports of the detection of hyperechogenic bowel using ultrasound there have been numerous cases in which cystic fibrosis developed in neonates in which this finding was detected antenatally in fetuses. In the study by Dicke and Crane 13% of the patients in their study with hyperechogenic bowel had cystic fibrosis as compared to .05% expected in the general population. Cystic fibrosis is said to be the most common autosomal recessive disesase affecting Caucasions. The gene responsible for the development of cystic fibrosis was discovered in 1989. The gene was identified on the long arm of chromosome 7 at region q(31). Most cases of cystic fibrosis (>70%) are due to the ?F 508 allele. Genetic testing is not perfect as there are 400-500 other cystic fibrosis alleles and differences between different ethnic groups. As the fetus and neonate will only develop cystic fibrosis if both parents are carriers, testing of parental blood for carrier status using DNA probes can be carried out in a large percentage of the population, when indicated.
Three studies reported in 1996 evaluated the association of cystic fibrosis with hyperechogenic bowel. In the study by Slotnick and Abuhamad, they analyzed the relationship between echogenic bowel and cystic fibrosis and aneuploidy in 145 patients found to have hyperechogenic bowel. They subjectively "quantitated" the degree of echogenicity by comparing the echogenicity to the fetal iliac bone, with 0 being normal and the brightest bowel having a score of 3. Of the 40 fetuses with a score of 1, with mild increase in bowel echogenicity, none had cystic fibrosis or aneuploidy. Of those fetuses with a score of 2, moderately increased echogenicity, 2 patients had cystic fibrosis and 2 had aneuploidy. In the 24 cases with a score of 3, markedly increased bowel echogenicity, 5 patients had cystic fibrosis and 6 had trisomy 21. In the study by Sepulveda et al cystic fibrosis testing was performed in 45 pregnancies in which there was echogenic bowel. Three carriers for cystic fibrosis were detected, however no cases of cystic fibrosis subsequently developed in any of these fetuses. Their conclusion was that " the prevalence of cystic fibrosis mutations is not increased in a low-risk population of pregnancies complicated by fetal echogenic bowel". In a study of bowel abnormalities in the fetus, not limited to cases of echogenic bowel, Corteville et al found that six of the fetuses with dilated and hyperechogenic fetal bowel had gastrointesintal abnormalities diagnosed after birth, including three with cystic fibrosis. They concluded that hyperechoic bowel in conjunction with dilated bowel was more predictive of cystic fibrosis than was hyperechoic bowel alone, 3 of 10 vs 1 of 33.
Numerous songraphic findings have been described in fetuses subsequently found to have trisomy 21. In the past 10 years cases of echogenic bowel in fetuses with trisomy 21 have been reported. While in many cases there are other sonographic findings eg nuchal thickening, short limbs; cases of echogenic bowel being the only sonographic finding have been reported in fetuses with trisomy 21. Dicke and Crane found one case of Trisomy 18 in which echogenic bowel was the only finding. They concluded that cytogenetic testing should be reserved only for those fetuses with other strucural abnormalties. While virtually all of the reported cases of echogenic bowel and fetal trisomies have been described in the second trimester, a report by Sepulveda et al described a case of trisomy 21 in which normal bowel was seen in the second trimester but became echogenic in the third trimester.
The incidence of chromosomal abnormalities in patients with echogenic bowel is between 3.3% reported by Dicke and Crane and 25-27% reported by Scioscia et al and Nyberg et al. In the study by Bromley et al hyperechogenic bowel was found in 0.6% of patients. Of 50 fetuses with echogenic bowel 58% were normal and 16 of the fetuses were aneuploid. They noted 12.5% of fetuses with trisomy 21 diagnosed by second trimester karyotyping had hyperechogenic bowel. As a result of their findings, their estimate of the hypothetical calculated risk for having a trisomy 21 fetus when hyperechogenic bowel is the only finding is 1.4%.
In the study of Dicke and Crane echogenic bowel was associated with fetal growth retardation in 23% and perinatal death in 17%. Other groups have also noted these associations. When echogenic bowel is seen in pregnancies in which the maternal serum AFP is elevated the pronosis is poor. In the study by Achiron et al all six fetuses with the combination of elevated maternal serum AFP and echogenic bowel were growth retarded. Four of these fetuses died in utero and one of the two live-born infants died in the neonatal period.
Fakhry J, Reiser M, Shapiro LR et al. Increased echogenicity in the lower fetal abdomen: a common normal variant in the second trimester. J Ultrasound Med 5:489, 1986
Lince DM, Pretorius DH, Manco-Johnson ML. The clinical significance of increased echogeniciy in the fetal abdomen. Amer J Roentgenol 145:683, 1985
Dicke JM, Crane JP. Sonographically detected hyperechoic fetal bowel: significance and implication for pregnancy management. Obstet Gynecol 80:778-782, 1992
Sepulveda W, Bower S, Fisk NM. Third-trimester hyperechogenic bowel in Down syndrome. Am J Obstet Gynecol 172:210-211, 1995
Bromley B, Doubilet P, Frigoletto FD, Krauss C, Estroff JA, Benacerraf BR. Is fetal hyperechoic bowel on second-trimester sonogram an indication for amniocentesis? Obstet Gynecol 83:647-651, 1994
Slotnick RN, Abuhamad AZ. Prognostic implications of fetal echogenic bowel. Lancet 347:85-87, 1996
Rypens FF, Avni EF, Absehsera MM, Donner C, Vermeylen DF, Struyven JL. Areas of increased echogenicity in the fetal abdomen: diagnosis and significance. Radiographics 15:1329-1344, 1995
Scioscia AL, Pretorius DH, Budorick NE, Cahill TC, Axelrod FT, Leopold GR. Second-trimester echogenic bowel and chromosomal abnormalities. Am J Obstet Gynecol 167:889-894, 1992
Sepulveda W, LeungKY, Robertson ME, Kay E, Mayall ES, Fisk NM. Prevalence of cystic fibrosis mutations in pregnancies with fetal echogenic bowel. Obstet Gynecol 87:103-106, 1996
Corteville JE, Gray DL, Langer JC. Bowel abnormalities in the fetus-correlation of prenatal ultrasonographic findings with outcome. Am J Obstet Gynecol 175:724-9, 1996
Achiron R, Seidman DS, Horowitz A, Mashiach S, Goldman B, Lipitz S. Hyperchogenic fetal bowel and elevated serum alpha-fetoprotein: a poor fetal prognosis. Obstet Gynecol 88:368-371, 1996
Home | Teaching Files | Literature | Bulletin Board