**Core Concept:** Hirschsprung's disease is a congenital gastrointestinal disorder characterized by the absence of functioning neurons in the distal portion of the colon, leading to impaired bowel motility and constipation.

**Why the Correct Answer is Right:** Hirschsprung's disease is caused by the absence of enteric neurons in the myenteric (Auerbach's) plexus and submucosal (Meissner's) plexus in the distal colon, resulting in impaired colonic smooth muscle contraction and impaired peristalsis. This leads to constipation, obstructive megacolon, and, in severe cases, megacolon with rectal distension and volvulus, which can be life-threatening.

**Why Each Wrong Option is Incorrect:**

A. **Absence of ganglion cells:** This is incorrect because the correct answer focuses on the absence of enteric neurons, not ganglion cells.

B. **Increased smooth muscle:** This is incorrect because Hirschsprung's disease is caused by the absence of enteric neurons, not increased smooth muscle.

C. **Developmental delay:** This is incorrect as it does not address the specific underlying cause of the disorder - the absence of enteric neurons.

D. **Neuroblastoma:** This is incorrect because Hirschsprung's disease is a congenital disorder, whereas neuroblastoma is a malignant childhood tumor of neural crest cells.

**Clinical Pearl:** Hirschsprung's disease is often diagnosed in infancy or early childhood, and its management may involve surgical options like pull-through procedures to establish a functional anastomosis between the rectosigmoid colon and the distal small bowel, ensuring adequate transit of feces from the colon to the rectum.

**Correct Answer:** D. Absence of enteric neurons (Hirschsprung's disease)