Large Bowel Obstruction

Large bowel obstruction is generally more difficult to diagnose than small bowel obstruction because there is considerable variability in the diameter of the normal fetal colon. The colon diameters of normal fetuses can overlap with those of fetuses with abnormally distended large bowel. During the latter part of the third trimester, the normal fetal colon can be particularly prominent and striking and could be mistaken as abnormal.

Incidence: About 1 in 2000 births.

Sonographic findings:

  • Dilated colon with or without dilated small bowel. Fig1
  • Dilated V- or U-shaped segment of bowel in the fetal pelvis suggestive of anorectal atresia. Fig2
  • Calcified intraluminal meconium. Fig3
  • The sensitivity of ultrasound for the diagnosis is rather low.
  • Congenital duplication of the cecum or colon shows peristaltic cyst with haustra at the lower abdomen, which may mimic colonic obstruction.

Fig 1:  Meconium ileus  Cross-sectional scan of the abdomen: Markedly dilated transverse colon (*) with meconium contents

Fig 2:  Anorectal atresia   Oblique cross-sectional scan of the abdomen: U-shaped cystic mass located at the lower abdomen (*), separated from the bladder (arrowhead=spine)

Fig 3:  Hyperechoic colon  Cross-sectional scan of the abdomen: hyperechoic colon (solid circle) (arrowhead = spine)

Video clips of large bowel obstruction

Distal bowel obstruction:  Cross-sectional scan of the lower abdomen: dilated rectum (*), the lesions became proven to be Hirschprung disease in neonatal life (this may be temporary normal variant) (solid circle = bladder)

Anorectal obstruction:  Dilated rectum and sigmoid colon resulting in V-shape appearance secondary to anorectal atresia

Anorectal atresia:  Anorectal atresia with ruptured large bowel: Oblique cross-sectional scan of the abdomen shows ascites with dilated rectum (R) and sigmoid colon

Associations: Related to other malformations in most cases including VACTERL syndrome, multiple congenital anomalies, caudal regression syndrome, and abnormal chromosome (15%).

Management: A careful search for associated anomalies is indicated. In general the disorder does not alter the standard obstetric care, however, the pregnancy should be managed in a tertiary center.

Prognosis: Poor overall (due to associated anomalies and prematurity), but good in isolated cases with surgical correction.

Recurrence risk: Sporadic with rare familial cases.