How is Hirschsprung's disease definitively diagnosed?

Hirschsprung's disease is definitively diagnosed through a rectal biopsy. This procedure involves taking a small sample of tissue from the rectum, which is then examined for the absence of ganglion cells in the intestinal wall. In Hirschsprung's disease, there is a lack of these nerve cells in a segment of the bowel, which is critical in regulating bowel movements. The presence of ganglion cells indicates normal function, while their absence confirms the diagnosis of Hirschsprung's disease.

The significance of the rectal biopsy also lies in its ability to provide direct evidence of the condition, making it the gold standard for diagnosis. This is particularly important in distinguishing Hirschsprung's disease from other forms of constipation in children, which can present similarly but have different underlying causes and treatments. Other diagnostic tools, although useful in preliminary assessments or in shaping the clinical picture, do not provide the definitive diagnosis that a biopsy does.