|
ANATOMY OF THE FETAL
COLON |
- Can be visualized as early as 22 weeks GA.
- Wide variation in diameter but rarely exceeds 23-26 mm (1).
- The length of contiguous bowel segments that are visible increases progressively with gestational age (1).
- The echo pattern is usually hypoechoic with respect to the liver and bowel wall but may occasionally be hyperechoic. After 14 weeks gestation, meconium collects in the colon. This is usually hypoechoic but may be hyperechoic.
- The characteristic course of the colon readily permits its distinction from pathologically dilated small bowel. Haustral folds, which can be frequently demonstrated, helps differentiate small from large bowel loops. In early gestation, haustral folds appear as thin linear echoes within the lumen of the colon. Later in gestation, the colon diameter increases and the haustral folds become longer and thicker.
|
|
22 weeks of
gestation |
|
|
28 weeks of
gestation |
|
|
|
|
GA (wks) |
Colonic Haustral Folds |
|
10-15 |
0% |
- Peristalsis.
- Colonic
diameter (Table) – Goldstein et.al. 1987
- Colonic diameter (Graph)– Goldstein et.al. 1987
PITFALL – THE PRESACRAL PSEUDOMASS (2,3) |
Do not mistake normal colon for a pelvic mass.
6.3% of third trimester fetuses may have a hypoechoic presacral mass measuring 15-30 mm. This represents the meconium filled rectum in the term fetus.
|
|
PITFALL – NON-OBSTRUCTED COLONIC DILATATION IN UTERO |
28 weeks gestation.
Large bowel measures 1.82cm. No obstruction demonstrated on postnatal investigations,
including rectal biopsy.
REFERENCES |
- Parulekar SG. Sonography of normal fetal bowel. J Ultrasound Med 1991;10:211-220.
- Karcnik T, Rubenstein JB, Swayne LC. The fetal presacral pseudomass: a normal sonographic variant. J Ultrasound Med 1991;10:579-581.
- Moreland SI III, Cohen MI, Leopold GR et.al. Third trimester fetal sonography: meconium simulating a presacral mass. AJR 1988;150:379-380.