**Question:** Commonest cause of intestinal obstruction in children is

A. Meckel's Diverticulum
B. Fistula
C. Gastrointestinal Stromal Tumor
D. Hirschsprung's Disease

**Correct Answer:** D. Hirschsprung's Disease

**Core Concept:**
Hirschsprung's Disease (HD) is a congenital disorder characterized by the absence of ganglion cells in the distal part of the enteric nervous system, leading to a decreased number of intramural neurons responsible for smooth muscle contraction and relaxation in the colon. This results in impaired colonic motility and ultimately, the development of intestinal obstruction.

**Why the Correct Answer is Right:**
Hirschsprung's Disease is the commonest cause of intestinal obstruction in children due to the following reasons:

1. **Increased intramural neurons in the aganglionic segment:** In Hirschsprung's Disease, there is a deficiency of neurons in the ganglionic cells, leading to a decrease in intramural neurons responsible for smooth muscle contraction and relaxation in the colon. This results in impaired colonic motility and the development of intestinal obstruction.
2. **Affected segment is the rectosigmoid colon and rectum:** The disease primarily involves the rectosigmoid colon and rectum, which are responsible for the storage and propulsion of fecal matter. This specific segment involvement contributes to the high incidence of intestinal obstruction in Hirschsprung's Disease cases.
3. **Predominantly affects children:** Hirschsprung's Disease is more common in children than adults due to incomplete development of ganglion cells during embryonic life.

**Why Each Wrong Option is Incorrect:**

A. Meckel's Diverticulum: A Meckel's Diverticulum is a congenital remnant of the omphalomesenteric duct, which is a normal anatomical variation present in the majority of the population. While Meckel's Diverticulum can rarely cause intestinal obstruction due to diverticulitis, intussusception, or gastrointestinal bleeding, it is not the commonest cause of intestinal obstruction in children.

B. Fistula: Fistulae are abnormal connections between two normally separated organs or spaces. Intestinal obstruction caused by a fistula is usually secondary to an underlying condition, like tuberculosis or Crohn's disease, rather than the primary cause of obstruction itself.

C. Gastrointestinal Stromal Tumor (GIST): Gastrointestinal stromal tumors are benign tumors originating from the interstitial cells of Cajal. Although GISTs can cause intestinal obstruction, they are relatively rare in children, making them less likely as the primary cause of intestinal obstruction compared to Hirschsprung's Disease.

D. Hirschsprung's Disease: As explained above, Hirschsprung's Disease is the commonest cause of intestinal obstruction in children due to the absence of ganglion cells in the affected segment, leading to impaired motility and dilation of the colon.

**Clinical Pearls:**
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