Okay, let's tackle this question. The patient is a male infant with abdominal distension after birth and less meconium passage. The key here is the clinical presentation. When an infant has these symptoms, I'm thinking about intestinal obstruction. Common causes in newborns include Hirschsprung's disease, which is a congenital absence of ganglion cells in the myenteric and submucosal plexuses of the colon.

The question mentions a full-thickness rectal biopsy. Full-thickness biopsies are gold standard for diagnosing Hirschsprung's. The biopsy would show absence of ganglion cells and increased number of nerve fibers in the affected segment. This is because Hirschsprung's is due to a failure of neural crest cells to migrate, leading to aganglionosis.

Looking at the options, the correct answer should be the one that states absence of ganglion cells and hypertrophy of nerve fibers. The other options might include things like normal ganglion cells (which would rule out Hirschsprung's), inflammation (like in infectious causes), or other structural issues. Each of those would be incorrect because they don't align with the pathophysiology of Hirschsprung's.

The clinical pearl here is that Hirschsprung's is a key consideration in neonates with delayed meconium passage and abdominal distension. The biopsy findings are definitive. So the correct answer would be the one that points to those specific histological changes.

**Core Concept** This question tests the pathophysiology of Hirschsprung's disease, a congenital aganglionic megacolon caused by the failure of neural crest cells to migrate to the distal bowel. A full-thickness rectal biopsy is diagnostic, revealing absence of ganglion cells and hypertrophied nerve fibers.

**Why the Correct Answer is Right** In Hirschsprung's disease, the rectal biopsy shows **aganglionosis** (absence of ganglion cells) in the myenteric (Auerbach's) and submucosal (Meissner's) plexuses. The biopsy also demonstrates **hypertrophied and hyperplastic nerve fibers** due to unopposed acetylcholine release from non-innervated smooth muscle. This "string of beads" appearance is pathognomonic.

**Why Each Wrong Option is Incorrect**
**Option A:** Normal ganglion cells would rule out Hirschsprung's disease.
**Option B:** Inflammation or fibrosis suggests other conditions (e.g., colitis) but not congenital aganglionosis.
**Option C:** Presence of ganglion cells in the biopsy indicates the transitional zone or normal bowel, not the aganglionic segment.

**Clinical Pearl / High-Yield Fact** Remember: **Hirschsprung's = AGANGLIONIC COLON + STRING OF BEADS ON BIOPSY**. Always associate delayed meconium passage (<24 hours), abdominal distension, and failure to thrive with this diagnosis. The biopsy confirms the diagnosis, while imaging (e.g., contrast enema) shows transition zones. **Correct Answer: C. Absence of ganglion cells with hypertrophied nerve fibers**

✓ Correct Answer: B. Lack of ganglion cells