Congenital Megacolon (Hirschsprung’s disease)

1. Congenital Megacolon (Hirschsprung’s disease) 소아과 R3 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)

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. 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