What is the diagnosis for a 2-month-old baby who is not passing gas?

Differential Diagnosis for a 2-Month-Old Not Passing Gas

A 2-month-old infant who is not passing gas requires urgent evaluation for bowel obstruction, with the differential diagnosis including distal bowel obstruction (Hirschsprung disease, meconium plug syndrome, ileal atresia), functional constipation, or less commonly, malrotation with volvulus—all of which can present with failure to pass gas and stool. 1

Critical Initial Assessment

The absence of gas passage is a red flag that distinguishes this from benign conditions like gastroesophageal reflux. You must immediately determine:

• Meconium passage history: No passage of meconium in the first 48 hours of life strongly suggests distal bowel obstruction, particularly Hirschsprung disease 1
• Current stool pattern: Complete absence of stool passage versus decreased frequency 2
• Abdominal distension: Presence indicates obstruction requiring urgent imaging 1
• Vomiting characteristics: Bilious vomiting suggests obstruction distal to the ampulla of Vater and requires emergency evaluation for malrotation with volvulus 1, 3
• Feeding tolerance: Poor feeding or refusal suggests significant pathology 4

Most Likely Diagnoses Based on Clinical Presentation

If No Meconium Passage or Delayed Passage (>48 hours after birth):

Hirschsprung disease is the primary concern when an infant has chronic constipation with failure to pass gas, particularly if meconium passage was delayed beyond 48 hours of life 1, 2

Distal bowel atresia (ileal or colonic) presents with failure to pass meconium, abdominal distension, and no gas passage 1

If Meconium Passed Normally but Now Not Passing Gas:

Functional constipation can occur even at 2 months, though less common than in older infants 5

Meconium plug syndrome may present with delayed symptoms if incompletely cleared 1

Diagnostic Approach

Physical Examination Must Include:

• Abdominal examination: Palpate for distension, masses, or tenderness 3, 4
• Digital rectal examination: Essential to assess for impacted stool, anal patency, and may be therapeutic in meconium plug syndrome 1
• Lower back inspection: Look for cutaneous markers of spinal dysraphism (dimples, hair tufts, skin discoloration) that suggest neurologic causes of bowel dysfunction 2

Initial Imaging:

Plain abdominal radiograph is the first-line imaging to assess bowel gas pattern, looking for dilated loops, air-fluid levels, or absence of distal gas 1, 2

Contrast enema is the diagnostic procedure of choice when radiographs show distal bowel obstruction pattern (multiple distended loops with absent or decreased distal gas) 1, 2. This differentiates between:

• Structural causes requiring surgery (atresia, Hirschsprung disease showing microcolon)
• Functional causes requiring observation or therapeutic enema (meconium plug)

Management Algorithm

If Abdominal Distension + Abnormal Radiograph:

1. NPO status and nasogastric decompression 3
2. IV fluid resuscitation for hydration 3
3. Urgent surgical consultation for suspected mechanical obstruction 1
4. Contrast enema for both diagnosis and potential treatment (therapeutic in meconium plug) 1, 2

If No Distension + Normal Examination:

1. Rectal stimulation with glycerin suppository or thermometer may be diagnostic and therapeutic 5
2. Close observation with instructions to return immediately if vomiting (especially bilious), distension, or feeding intolerance develops 3
3. Consider dietary factors in breastfed infants (maternal diet) or formula-fed infants (formula type) 6, 7

Critical Pitfalls to Avoid

Do not dismiss this as simple constipation without thorough evaluation, as Hirschsprung disease can present subtly at 2 months and delayed diagnosis leads to enterocolitis with significant morbidity and mortality 1, 4

Malrotation with volvulus can present at any age, not just newborns—maintain high suspicion if any bilious vomiting develops, as this requires emergency surgery 1, 3

Neurologic causes (tethered cord, spinal dysraphism) are easily missed without careful back examination and can cause chronic bowel dysfunction 2

Do not use stimulant laxatives or enemas repeatedly without establishing a diagnosis, as this delays appropriate treatment for structural causes 5