Congenital Megacolon

Congenital megacolon

Congenital aganglionic megacolon (Hirschsprung's disease) is caused by the absence of intestinal innervation that affects the internal anal sphincter and the adjacent proximal segment.

Epidemiology

• It is the most common cause of lower GIT obstruction in newborns;
• its incidence is 1:5000 live births;
• boys are affected 4 times more often than girls;
• and it may be associated with other birth defects (i.e: trisomy 21 or medullary thyroids carcinoma).

Etiopathogenesis and Pathophysiology

• a disorder of neuroblast migration from the proximal to the distal intestine with consequent absence of ganglion cells in the intestinal wall;
• histologically: absence of Meissner's and Auerbach's plexus with hypertrophic nerve endings and high concentration of acetylcholinesterase;
• short-segment disease aka the classical form(75%): aganglionosis in the rectosigmoid colon;
• long-segment disease (10%): aganglionosis in the whole colon
• ultra-short segment disease: aganglionosis in the rectum that is 1-3 cm long;
• the aganglionic region is permanently contracted (inhibiting neurons are missing) which causes a functional obstruction → thus, the healthy intestine dilates above it and hypertrophies to form a megacolon.

Clinical Picture

• in 90% of cases, manifestation begins immediately after birth;
• milder forms: chronic constipation, growth failure, gradually developing abdominal distension with an increase in pathogens and symptoms of enterocolitis to sepsis;
• the onset of difficulties is typical in infancy (often after the introduction of non-dairy foods): increased tone of the internal sphincter, small volume of stool during defecation, or no defecation;
• in ultrashort segment disease, stools accumulate in the rectum and the sphincters gradually weaken. Thus smearing + paradoxical diarrhea (soiled laundry).

Diagnosis

Histopathological specimen of Hirchsprung's disease showing fibers containing abnormal ACHE (brown) in the lamina propria mucosae.

Hirschsprung's disease
A–C Plain abdominal radiographs
D–E X-ray with contrast agent

• irigography – after previous emptying of the intestine by enemas, delayed evacuation, transition zone between the narrow distal aganglional segment and the proximally dilated section of the intestine; defecogram;
• anorectal manometry - measurement of anal pressure when inflating a balloon in the rectum (anal pressure does not decrease or it paradoxically increases);
• rectal biopsy - may be false negative in the ultrashort segment.

Therapy

• surgical solution: good prognosis, most patients have preserved continence.

Complications

• Toxic megacolon - can lead to sepsis with a risk of secondary meningitis or intestinal perforation.

Notes

• Megacolon idiopaticum : a disorder of vegetative innervation - the disparity between the sympathetic and parasympathetic .
• Megacolon symptomaticum : dilatation above the stenotic site - eg. congenital stenosis, scar after surgery…

References

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