ANATOMY OF THE SMALL INTESTINES  

In early gestation (10-20 weeks), the small bowel lumen is difficult to demonstrate. The region of the small bowel appears as a hyperechoic area (relative to the fetal liver), in the abdomen and pelvis. This hyperechoic appearance around the small bowel persists throughout pregnancy. Between 12-16 weeks, this hyperechoic area occupies a large portion of the fetal pelvis and lower abdomen.

Criteria for normality include:

As the gestation progresses, the hyperechoic area becomes less prominent and is more centrally located in the fetal abdomen (1).

The hyperechoic appearance is thought to be due to:

  1. Reflections from walls of collapsed loops of small bowel.
  2. Mesenteric fat between loops of collapsed small bowel, as later in gestation, spaces between loops of fluid-filled small bowel also appear hyperechoic.

This hyperechoic area may be unusually prominent and should not be mistaken for a pathologic mass (2,3). Follow up scans in a few weeks will show a change in appearance or disappearance of this hyperechoic area (1).

Between 13-20 weeks, hypoechoic rounded areas may develop within this hyperechoic region and probably represent small bowel lumen. Later in pregnancy, longer segments of fluid-filled small bowel loops can be demonstrated as rounded areas, however valvulae conniventes are only visualized in a small percentage of patients (1).

 

 

 

 

GA (wks)

Small Bowel Peristalsis

10-15
15-20
20-25
25-30
30-35
35-40
>40

0%
0%
0%
9%
47%
73%
77%

 

 

 

 

 

 

REFERENCES
  1. Parulekar SG. Sonography of normal fetal bowel. J Ultrasound Med 1991;10:211-220.
  2. 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 1986;5:489.
  3. Lince DM, Pretorius DH, Manco-Johnson ML. The clinical significance of increased echogenicity in the fetal abdomen. AJR 1985;145:683.