**Question:** Biopsy in Hirschsprung's disease can be taken from:

A. rectal mucosa
B. submucosa
C. muscularis propria
D. muscularis mucosae

**Correct Answer:** .

**Core Concept:**
Hirschsprung's disease is a congenital disorder characterized by the absence of ganglion cells in the myenteric and submucosal plexuses of the distal colon, leading to impaired bowel motility and constipation. A biopsy is essential to confirm the diagnosis and differentiate it from other conditions like aganglionic megacolon.

**Why the Correct Answer is Right:**
In Hirschsprung's disease, the biopsy is taken from the muscularis propria, where ganglion cells are absent. This helps in confirming the diagnosis and ruling out other conditions. The muscularis propria is the layer between the internal and external circular muscles and is the site where ganglion cells are typically found in normal bowel.

**Why Each Wrong Option is Incorrect:**

A. Rectal mucosa: This option is incorrect because the biopsy should be taken from the muscularis propria, not the mucosa which is normally rich in ganglion cells and would not confirm the absence of ganglion cells seen in Hirschsprung's disease.

B. Submucosa: Similar to rectal mucosa, the biopsy should be taken from the muscularis propria, not the submucosa. The submucosa contains ganglion cells and would not confirm the absence of ganglion cells in Hirschsprung's disease.

C. Muscularis mucosae: This is incorrect because the biopsy should be taken from the muscularis propria, not the muscularis mucosae. The muscularis mucosae contains ganglion cells and would not confirm the absence of ganglion cells in Hirschsprung's disease.

D. Muscularis externa: This is also incorrect as the biopsy should be taken from the muscularis propria, not the muscularis externa. The muscularis externa contains smooth muscle fibers and would not confirm the absence of ganglion cells in Hirschsprung's disease.

**Clinical Pearl:**
Hirschsprung's disease is typically diagnosed by demonstrating the absence of ganglion cells in the muscularis propria layer, which is the correct target for biopsy. Failure to find ganglion cells in this layer would suggest Hirschsprung's disease, while finding ganglion cells in mucosa, muscularis mucosae, muscularis externa, and rectal mucosa would be inconsistent with the disease and indicate an incorrect site for biopsy.