1. Congenital Megacolon (Hirschsprung’s disease)
안선영

2. Incidence
absence of ganglion cells in the bowel wall beginning in the internal anal sphincter and extending proximally
1/5000 live births
M:F = 4:1
Racial distribution similar

3. Embryology and Etiology
Neuroenteric cells migrate from neural crest to upper end of alimentary tract and proceed in distal direction
12th week : migration to distal colon – first into myenteric (Auerbach’s plexus) then into submucosal plexus
Embryologic defect

4. Failure of neural crest migration
Immunologic mechanism: increased expression of class II antigens in the mucosa and submucosa-> causes fetus to mount an immunologic response against the neuroblast
Genetic factors: May affect more than one family member in 3-7% of cases
Deletion in the RET gene chromosome 10q11 and EDNRB gene located on 13q22 and EDN 3 gene (major role in the development of the enteric nervous system)
Endothelin receptor B, endothelin 3

5. Pathology Neonatal period: intestine is normal
Proximal ganglionic intestine hypertrophies and becomes thicker and longer than normal
Taeniae disappear and longitudinal muscle layer completely surrounds colon
Distal intestine: absence of ganglion cells in the submucosal (Meissner’s) plexus and myenteric (Auerbach’s) plexus
Marked increase in nerve fibers which extend into the submucosa (seen with acetylcholinesterase stain)
Aganglionosis extends to rectosigmoid region in 80% of cases

6. Clinical Symptoms
Should be considered in any child who has history of constipation dating to newborn period
90% of cases diagnosed in newborn period
Most common presentation in newborns: delayed stool passage within first 48 hrs of life
Constipation, abdominal distension, poor feeding and vomiting
Constipation followed by explosive diarrhea, failure to thrive
in older children, large fecal mass palpable in left lower quadrant. rectum is empty
stools: small pellets, ribbon-like, fluid consistency

7. Rectal exam: normal anal tone followed by explosive discharge of feces and gas
failure to pass stool leads to dilatation of proximal bowel -> increased intraluminal pressure, decreased blood flow and deterioration of the mucosal barrier
stasis leads to bacterial proliferation and enterocolitis with sepsis
early diagnosis important in reducing mortality

8. Study of 123 patients with HD
60% were diagnosed in neonatal period
Delayed passage of meconium (65%), abdominal distension and constipation
17% had associated anomalies
86% had aganglionosis extending to rectosigmoid region

9. Associated Anomalies Present in 10-30% of HD
Urogenital tract (11%), cardiovascular system (6%), GI system (6%), other malformations, cataract, cleft palate (8%)
3% Down SD

10. Diagnosis I
Abdominal x-rays: air fluid levels in colon and distended loops of intestine
Barium enema: narrow distal segment and dilated proximal intestine; presence of funnel-shaped transition zone between these 2 segments (diagnostic accuracy 80-90%)
Transition zone may not be present before 1-2 weeks of age
significant barium remaining in colon in 24-hr delayed film
helpful in determining level of aganglionosis
Should not be done with clinical enterocolitis: may cause perforation

11. Diagnosis II
Anorectal manometry: absence of relaxation reflex after distension of balloon in rectum
Diagnostic
accuracy 85%
May be done at bedside or as outpatient procedure : no complications
Test unreliable in cases where gestational age plus age after birth is less than 39 weeks and weight is less than 2.7kg

12. Diagnosis III Rectal biopsy: gold standard
Can be performed at bedside without general anesthesia
Biopsy taken at 2 cm, 3 cm, 5 cm above dentate line
Diagnostic accuracy: 99.7%
Most common problem is inadequate specimen (insufficient amount of submucosa)

13. Differential diagnosis
Meconium plug SD, small left colon SD, distal ileal atresia, low imperforate anus
Neonatal sepsis, hypothyroidism, brain injury, prematurity may result in delayed passage of stool

14. Treatment Decompression: nasogastric tube, rectal tubes
perform surgery after diagnosis established or perform temporary colostomy until infant is 6-12 mos old
3 basic surgical approaches:

15. Swenson: excise aganglionic segment and anastomose the normal proximal bowel to the rectum 1-2 cm above the dentate line
Duhamel: neorectum created-> normally innervated bowel brought down behind aganglionic rectum: anterior aganglionic half with normal sensation and posterior half ganglionic with normal propulsion

16. Ultrashort segmental HD: excision of strip of rectal muscle
3) Soave: endorectal pull-through procedure-> strip mucosa from the aganglionic rectum and bring normally innervated colon through the residual muscular cuff
Ultrashort segmental HD: excision of strip of rectal muscle

17. Complications
Early complications: anastomotic strictures (15%), wound infections (11%), anastomotic leaks (7%)
Late complications: chronic constipation, enterocolitis, encoporesis
Good prognosis: more than 90% of children achieve normal bowel movement