Megacolon congenitum

Congenital aganglionic megacolon (Hirschsprung's disease) is caused by abnormal innervation of the bowel, affecting the internal anal sphincter and the adjacent proximal segment of variable length.

Epidemiology

 * the most common cause of obstruction of the lower GIT in newborns;
 * incidence 1:5000 live births;
 * boys affected 4x more often than girls;
 * may be associated with other birth defects, trisomy 21 or medullary carcinoma of the thyroid gland.

Etiopathogenesis and pathophysiology

 * disorder of neuroblast migration from the proximal to the distal intestine with subsequent 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;
 * classic form (75%): aganglionosis in the rectosigmoid; in 10% the entire colon is affected; ultrashort form: aganglionic section in the rectum 1-3 cm long;
 * the aganglionic section is permanently contracted (missing inhibitory neurons) and causes functional obstruction → the healthy intestine above it dilates and hypertrophies to form a megacolon.

Clinical picture

 * in 90% of cases, manifestation immediately after birth: late departure of the pitchfork;
 * milder forms: chronic constipation, failure to thrive, gradually developing abdominal distension with overgrowth of pathogens and symptoms of enterocolitis to sepsis;
 * the onset of difficulties in infancy is typical (often after the introduction of non-dairy foods): increased tone of the internal sphincter, small volume of stool during defecation, smearing does not occur;
 * for ultra-short English section, stool accumulates in the rectum, the sphincters gradually weaken, soiling + paradoxical diarrhea (dirty laundry).

Diagnosis

 * irrigography – after previous emptying of the intestine with enemas, delayed evacuation, transition zone between the narrow distal aganglionic segment and the proximally dilated section of the intestine; defecogram;
 * anorectal manometry – measurement of anal pressure when a balloon is inflated in the rectum (anal pressure does not decrease, or paradoxically increases);
 * rectal biopsy (may be false negative for ultrashort segment).

Therapy

 * surgical solution; prognosis is good, most patients maintain continence.

Complications

 * toxic megacolon with a septic course with the risk of secondary meningitis or bowel perforation.

Related Articles

 * Congenital atresias and stenoses of the gastrointestinal tract
 * pylorostenosis congenita
 * arteriae mesentericae superioris syndrome
 * intestinal malrotation and volvulus
 * small bowel obstruction
 * meconium ileus