Hirschsprung’s disease is a congenital condition where nerve cells of the myenteric plexus are absent in the distal bowel and rectum. The myenteric plexus, also known as Auerbach’s plexus, forms the enteric nervous system. It is the brain of the gut.
This nerve plexus runs all the way along the bowel in the bowel wall, and is a complex web of neurones, ganglion cells, receptors, synapses and neurotransmitters. It is responsible for stimulating peristalsis of the large bowel. Without this stimulation the bowel looses it’s motility and stops being able to pass food along its length.
The key pathophysiology in Hirschsprung’s disease is the absence of parasympathetic ganglion cells (Auerbach’s and Meissner’s plexus). During fetal development these cells start higher in the GI tract and gradually migrate down to the distal colon and rectum. Hirschsprung’s occurs when the parasympathetic ganglion cells do not travel all the way down the colon, and a section of colon at the end is left without these parasympathetic ganglion cells.
The length of colon without innervation varies between patients from a small area to the entire colon. When the entire colon is affected this is called total colonic aganglionosis. The aganglionic section of colon does not relax, causing it to becomes constricted. This leads to loss of movement of faeces and obstruction in the bowel. Proximal to the obstruction the bowel becomes distended and full.
Risk factors:
The severity of the presentation and the age at diagnosis varies significantly depending on the individual and the extent of the bowel that is affected. It can present with acute intestinal obstruction shortly after birth or more gradually developing symptoms: