Neonatal Distal Bowel Obstruction

Steven J. Kraus, MD

DIFFERENTIAL DIAGNOSIS

Common

Hirschsprung Disease (HD)
Meconium Plug Syndrome (MPS)

Less Common

Meconium Ileus (MI)
Jejunoileal Atresia

Rare but Important

Anorectal Malformation (ARM)
Midgut Volvulus (MV)
Omphalomesenteric Duct Remnant Obstruction
Rectal Atresia
Colonic Atresia

ESSENTIAL INFORMATION

Key Differential Diagnosis Issues

Findings of contrast enema (CE) limit differential diagnosis: Colonic vs. small bowel process
Antenatal or prenatal midgut volvulus late in natural history (ischemia); ileus can mimic distal bowel obstruction
Hirschsprung disease more common in patients with Down syndrome
Consider meconium ileus if family history of cystic fibrosis
Meconium plug syndrome associated with maternal Mg++ therapy, maternal diabetes
No rectal opening in male or single perineal opening in female patient with ARM
Abdominal radiographs: Many dilated bowel loops
- ± air-fluid levels
- If dilated bowel loops but no air-fluid levels, suspect meconium ileus
If CE and upper GI (UGI) normal in face of obstruction, consider omphalomesenteric duct remnant anomaly

Helpful Clues for Common Diagnoses

Hirschsprung Disease (HD)
- Often presents at birth with distal bowel obstruction
- Contrast enema primary findings
  - Rectosigmoid ratio < 1
  - Transition most commonly sigmoid
  - Transition often missed if at anorectal verge; enema misinterpreted as normal
- Other supporting CE findings
  - Distal colonic spasm
  - Colitis
  - Irregular contractions
  - Mucosal irregularity
  - Delayed evacuation
- Total colonic Hirschsprung
  - Small colon without transition ± intraluminal terminal ileal calcification
- Higher incidence in Down syndrome, especially total colonic disease
- Radiologic transition not equivalent to histologic transition, especially in long-segment HD
Meconium Plug Syndrome (MPS)
- Nonpathologic diagnosis
- Association with Mg++ therapy for preeclampsia and diabetic mother
- Presents clinically similar to Hirschsprung disease
- Enema findings
  - Rectosigmoid ratio > 1
  - Small left colon, abrupt transition to dilated bowel at splenic flexure, colonic meconium pellets
  - Evacuation of meconium during and after enema

Helpful Clues for Less Common Diagnoses

Meconium Ileus (MI)
- Possible radiographic findings
  - “Soap bubble” densities in right lower quadrant
  - Multiple dilated loops of air-filled bowel likely indicates simple MI
  - Air-fluid levels within bowel loops less likely due to thick meconium
  - Gasless abdomen indicates high risk of complicated MI
  - Peritoneal calcifications indicate meconium peritonitis (evidence of bowel perforation, complicated MI)
- Contrast enema findings
  - Microcolon
  - Small terminal ileum (TI) filled with meconium pellets
  - Dilated ileum proximal to obstructing meconium
- Possible ultrasound findings
  - Echogenic bowel loops
  - Meconium pseudocyst
  - Peritoneal calcifications
- Almost always associated with cystic fibrosis
Jejunoileal Atresia
- Possible radiographic findings
  - Multiple, dilated, air-filled bowel loops
  - Air-fluid levels within bowel loops
  - Gasless abdomen suggests bowel perforation
  - Peritoneal calcifications suggest meconium peritonitis due to bowel perforation
- Contrast enema findings
  - Rectosigmoid ratio > 1
  - Microcolon
  - Normal caliber TI without meconium
  - Refluxed contrast in TI abruptly terminates in ileum or distal jejunum

Helpful Clues for Rare Diagnoses

Anorectal Malformation (ARM)
- Imperforate anus or anteriorly located stenotic rectal orifice on physical exam in male
- Anterior stenotic rectal orifice or single perineal orifice on physical exam in female
- Distal bowel obstruction
  - Colon generally more compliant; dilates more than small bowel
Midgut Volvulus (MV)
- Late presentation: Dilated bowel due to ischemic ileus
- Radiographs show multiple dilated bowel loops
  - Sometimes pneumatosis or bowel wall thickening
- Normal caliber colon on CE
- UGI shows duodenal obstruction
  - Partial: Corkscrew with dilation of proximal duodenum
  - Complete: No contrast distal to obstruction
Omphalomesenteric Duct Remnant Obstruction
- Radiographs show dilated bowel loops of distal obstruction
- Contrast enema: Usually normal caliber colon; reflux contrast into beak-shaped, obstructed terminal ileum
- Normal duodenal rotation on UGI
- Volvulus of omphalomesenteric duct remnant
Rectal Atresia
- Radiographs show dilated bowel loops of distal obstruction
- Colonic loops usually dilate more than small bowel loops
- Contrast enema: Abrupt obstruction of colon just above anorectal verge
- Considered by some to be a type of anorectal malformation
Colonic Atresia
- Findings on radiographs similar to rectal atresia
- Contrast enema: Obstruction of colon proximal to rectum
- Etiology: Ischemic event in utero similar to small bowel atresias

Image Gallery

Anteroposterior fluoroscopic spot radiograph scout in an infant with infrequent stooling shows moderate to large stool load without other specific abnormality. The bones appear normal.