Hirschsprung's Disease (HD)

The congenital defect where nerve cells at the end of the bowel are missing is known as Hirschsprung’s disease (HD). This absence of ganglia at the distal end of the colon results in functional obstruction of the bowel where the stool moves really slowly or doesn’t move at all. HD should be considered as a potential diagnosis in any newborn baby who fails to pass meconium (i.e., the baby’s first stool) within the first 24 – 48 hours after birth.

The disorder typically and most often presents in the rectum and the sigmoid colon. However, there are cases where children may have nerve cells missing from the entire colon and/ or even part of the small intestine. These possibilities allow for the categorization of HD as short- or long-segment disease. In short-segment HD, only the last part of the large intestine has an absence of innervation. In contrast, long-segment HD presents as most or sometimes all of the large intestine missing cells, which may at times extend to the first part of the small intestine. However, extensive long-segment HD is very rare.

Pathophysiology

Under normal conditions, the intestines are innervated by a complex of enteric nerve plexuses (i.e., submucosal Meissner and myenteric Auerbach plexuses), which play imperative roles in bowel motility, secretion, absorption, and the regulation of blood flow. The enteric nervous system (ENS) is capable of managing all aspects of bowel function mostly without the assistance of the central nervous system (CNS). Thus, it basically functions as what may be called a second brain, with its own intrinsic and complex reflexive controls.

In order for the smooth muscles of the intestines to contract or relax to allow for the passage of bowel contents (e.g., stool), they must be innervated with enteric ganglia. These extensive neural circuits, which are capable of autonomous local control, possess extrinsic neural afferents that contain cholinergic and adrenergic fibers that are responsible for contraction and inhibition, respectively. Relaxation is generally mediated by nitric oxide and other neurotransmitters of the enteric system. In patients with HD, both of the enteric nerve plexuses are absent.

Loss of enteric autonomy leads to an attempted extrinsic takeover of smooth muscle control. However, this control is not balanced, because there is a predominance in excitatory signals over the inhibitory ones. This leads to an increase in smooth muscle tone that is unopposed due to the loss of intrinsic enteric reflexes. Functional obstruction of the bowel ensues due to the imbalance in smooth muscle contractility and the uncoordinated peristalsis (i.e., wave-like muscle contractions of the gut).

Epidemiology

HD is a condition that is estimated to affect about 1 in every 1500 – 1700 newborns worldwide and seems to have an occurrence three times more frequent in Asian-Americans compared to other races. Moreover, the disease has a greater predilection for males than in females with a male to female ratio of 4:1. Thanks to great strides in medicine and technology, most cases can be diagnosed in the neonatal period, much earlier than diagnosis at 2 – 3 years, which was the case in the early to mid 1900s.