Clinical Presentation Analysis

A 5-day-old neonate presents with:

• Abdominal distention
• Failure to pass meconium since birth
• Normal anal tone and an empty rectum
• Rapid expulsion of stool after digital examination (the "squirt sign")

These findings, particularly the combination of distal intestinal obstruction symptoms and the "squirt sign," strongly suggest Hirschsprung's disease.

Hirschsprung's Disease Explained

Hirschsprung's disease is a congenital condition where nerve cells (ganglion cells) are absent in a segment of the large intestine, usually starting at the rectum. This prevents the bowel from contracting normally, leading to obstruction.

Diagnostic Test Evaluation

The goal is to identify the test that definitively establishes the diagnosis of Hirschsprung's disease.

• Rectal Manometry: Assesses rectal muscle reflexes. While it can be abnormal in Hirschsprung's disease (absence of the rectoanal inhibitory reflex), it's not the primary method for establishing the diagnosis itself, especially in neonates.
• Barium Follow-Through Contrast Study: Can show characteristic features like a narrowed distal segment (aganglionic bowel) and a dilated proximal segment. However, results can be equivocal in neonates, and it doesn't provide histological confirmation.
• Rectal Suction Biopsy: This is the gold standard for diagnosing Hirschsprung's disease. It obtains a sample of the rectal mucosa and submucosa. Microscopic examination reveals the absence of ganglion cells, confirming the diagnosis.
• Colonoscopy: Primarily used for visualization and can be part of the workup, but it is not the primary test for establishing the diagnosis of Hirschsprung's disease based on the absence of ganglion cells. Biopsies taken during colonoscopy may not always reach the necessary submucosal layer.

Therefore, a rectal suction biopsy is the crucial test to confirm the absence of ganglion cells and establish the diagnosis.