• Irregular bowel movements and constipation are a common complaint pediatric complaint.
• The majority of cases are functional, but providers should take extra care to rule out organic causes like Hirschsprung's disease particularly during the neonatal period. 
• 1 in 5000 incidence, with abnormal innervation of the distal colon resulting in tonic contraction, and obstruction of feces.
• In most cases, the agangionic segment is limited to the rectosigmoid area.
• Symptoms usually begin in the first month of life and consist of obstuctive complications such as abdominal distension, bilious vomiting, and poor feeding.
• Rectal examination should be done in all patients with constipation, and often reveals a narrowed high-pressure region adjacent to the anal sphincter.
• Barium enema, anal manometry, and rectal biopsy all aid in the diagnosis.

References

NMS Pediatrics. Lippincott Williams and Wilkins. 4th Edition. Paul Dworkin editor.