Hirschsprung Disease

Pathogenesis

Characterized by aganglionated distal colon/rectum.
- Absence of ganglion cells in:
  - Myenteric (Auerbach) plexus.
  - Submucosal (Meissner) plexus.
Occurs in 1 in 5000 live births.
Boys are affected four times more frequently than girls.
Associations:
- 3%-5% of cases with Down syndrome.
- Increased risk with family history.
- Linked to RET oncogene on chromosome 10.

Muscular spasm of the distal colon and internal anal sphincter causes a functional obstruction.
Contracted distal bowel is abnormal, while the proximal bowel becomes dilated.
Aganglionosis begins at the anorectal line and affects:
- Rectosigmoid colon in 80% of cases.
- Splenic or transverse colon in 17%.
- Entire colon in 8%.
The area between the dilated and contracted segments is the transition zone.

>90% of infants present with:
- Abdominal distention.
- Bilious emesis.
- Failure to pass meconium within the first 24 hours of life.
Missed diagnoses in older children present with chronic abdominal distention and constipation.
Enterocolitis is the most common cause of death in untreated Hirschsprung disease.
- Symptoms: Diarrhea, obstipation, abdominal distention, fever, hematochezia, peritonitis.

Contrast enema:
- Narrow distal rectum with a transition zone.
- Failure to evacuate contrast after 24 hours indicates Hirschsprung disease.
Manometry study (in older toddlers): Shows high internal sphincter pressure upon rectal balloon distention.
Rectal biopsy (gold standard):
- Performed 2 cm above the dentate line in newborns using a suction biopsy kit.
- In older children, a full-thickness biopsy under general anesthesia.
- Histopathology shows absent ganglia, hypertrophied nerve trunks, and acetylcholinesterase staining.
- Calretinin immunostaining is a standard adjunct.

Advantages:
- Minimally invasive.
- Does not require leveling colostomy.
Steps:
1. Seromuscular biopsies of the distal colon to identify transition zone.
2. Dissection of distal rectum.
3. Endorectal mucosal dissection via transanal approach.
4. Coloanal anastomosis performed after pulling through ganglionated normal colon.
Transanal Soave Procedure: Entirely performed through the transanal approach.

Stool dysfunction, constipation, soiling, incontinence, and enterocolitis.
Histologic reevaluation required if complications persist.

Swenson Procedure:
- Aganglionic bowel removed down to internal sphincters.
- Coloanal anastomosis performed.
Duhamel Procedure:
- Aganglionic rectal stump left in place.
- Normal ganglionated colon pulled behind the stump.
- Stapling creates a neorectum with normal emptying.

Rarely performed today, except in cases of massively dilated colon.
- Initial diverting end colostomy may be necessary to allow colon shrinkage before coloanal anastomosis.

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