PATHOPHYSIOLOGY

Hirschprung’s disease or congenital aganglionic megacolon is a

bowel obstruction resulting to absence of ganglion cells in the myenteric plexus. It

is named after Harald Hirschsprung, the Danish physician who first described the

disease in 1886, describing two infants who had died with swollen bellies.

The ganglion cells reside in the adrenal medulla and are involved in the

SNS release of epinephrine and norepinephrine. They are special nerve cells in

the intestine that makes the muscles push stool to the anus. The myenteric

plexus is a major nerve supply in the GI system which controls GIT motility where

the ganglion cells enter. It is has two kinds namely-- Auerbach’s plexus and

Meissner’s plexus. Auerbach’s plexus provides motor innervations plus

secretomotor for PNS and SNS while Meissner’s plexus works parasympathetically

only. However, failure of the ganglion cells to migrate in the craniocaudal area

results to absent ganglion cells in the myenteric’s plexuses in the submucosa.

Parasympathetic innervation is depressed which results to uninterrupted

colonic, usually rectosigmoid, contraction. Decreased PNS stimulation signifies

inadequate expression of synaptic neurotransmitter, Ach and NO. Due to absence

of ganglion cells in the myenteric plexus, especially Meissner’s plexus, there is an

increase in synaptic activity of acetylcholinesterase, an enzyme which degrades

acetylcholine activity and a decrease of nitric oxide, an enzyme responsible for

the relaxation of smooth muscles in the endothelium in the recto-sigmoid

segment. Both of these factors inhibit relaxation of the contracted segments.

These strings of events will result to an ineffective peristaltic movement

that causes impaction of stool in the large intestines. Bowel distention also results

from impaction of feces and flatus.

The abdominal distention and fecal impaction will result to intestinal

perforation and constipation. Moreover, it will cause bacterial overgrowth in the

intestines and mucosal irritation of the linings of the intestines that may result to

complications such as enterocolitis and diarrhea, which is the most common

complication. If left untreated, hypovolemic shock will follow.

Absence of Ganglion Cells in Myenteric Plexuses

Bacterial Overgrowth Mucosal Irritation

Constipation

Inadequate expression of PNS stimulation(↑acetylcholinesterase, ↓NO)

Inhibits relaxation of contracted segment

Ineffective peristaltic movement

Bowel distention 2o to fecal stagnation and gas

Perforation

Enterocolitis and Diarrhea

(most common complication)

SHOCK