Pathophysiology Hirschprung’s Disease Or Congenital Aganglionic Megacolon Is A Bowel

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

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

Inhibits relaxation of contracted segment

Ineffective peristaltic movement

Bowel distention 2o to fecal stagnation and gas

Bacterial Overgrowth

Mucosal Irritation

Enterocolitis and Diarrhea (most common complication)

SHOCK

Perforation

Constipation