**Core Concept**
Hirschsprung's disease is a congenital condition characterized by the absence of **ganglion cells** in the distal bowel, leading to a functional obstruction. This condition is typically diagnosed in infancy but can occasionally be found in adults. The primary issue is the lack of **peristalsis** in the affected segment.

**Why the Correct Answer is Right**
The correct answer involves understanding the pathophysiology of Hirschsprung's disease, which includes the absence of **ganglion cells** in the **submucosal (Meissner's) and myenteric (Auerbach's) plexus**. This absence leads to a contracted segment of the bowel, which is typically the distal segment, and a dilated segment proximal to the obstruction. The disease can indeed be diagnosed in adults, although it's less common, and it primarily affects the **colon** but can extend to involve the small intestine in severe cases.

**Why Each Wrong Option is Incorrect**
**Option B:** The dilated segment is actually the portion of the bowel proximal to the obstruction, not the segment involved by the disease itself.
**Option C:** While it's true that **Auerbach's plexus** is involved, stating it's absent oversimplifies the condition, as the primary issue is the absence of ganglion cells within this plexus.
**Option D:** This option is partially correct but is not the best choice because Hirschsprung's disease primarily affects the colon, not the small intestine.
**Option E:** Bleeding per rectum is not the usual presentation; instead, symptoms typically include severe constipation, abdominal distension, and failure to pass meconium in newborns.

**Clinical Pearl / High-Yield Fact**
Hirschsprung's disease should be suspected in any newborn who fails to pass meconium within the first 48 hours of life. The condition requires surgical intervention to remove the aganglionic segment of the bowel.

**Correct Answer:** A. Sometimes found in adult.