Hirschsprung disease, also known as congenital aganglionic megacolon, is a developmental disorder characterized by the absence of enteric ganglia in a segment of the bowel. This absence leads to a failure of peristalsis in the affected segment, causing severe constipation or intestinal obstruction.
Histological Features
The hallmark of Hirschsprung disease in histology is the absence of the ganglion cells in the submucosal (Meissner's) and myenteric (Auerbach's) plexuses. These ganglion cells are crucial for the normal motility of the intestines. Instead of these ganglion cells, one might observe hypertrophic nerves in the aganglionic segment.
Diagnosis often involves a rectal biopsy. The biopsy is usually taken from the rectum because the disease most commonly affects the rectosigmoid colon. The specimen is then subjected to histological examination to identify the absence of ganglion cells.
Role of Immunohistochemistry
Immunohistochemistry (IHC) can be particularly useful in identifying the absence of ganglion cells. Stains such as calretinin are often used. In normal tissue, calretinin stains ganglion cells and nerve fibers, but in Hirschsprung disease, these cells are absent, confirming the diagnosis.
Pathophysiology
The pathophysiology of Hirschsprung disease involves the disruption of neural crest cells migration during embryonic development. These neural crest cells fail to populate the distal segments of the bowel, leading to the absence of enteric ganglia. This results in a functional obstruction and dilatation of the proximal bowel, while the distal segment remains contracted.
Clinical Implications
Clinically, patients with Hirschsprung disease present with symptoms of intestinal obstruction. Newborns may exhibit delayed passage of meconium, abdominal distention, and bilious vomiting. Older children may present with chronic constipation, abdominal distention, and failure to thrive.
Histological Differential Diagnosis
Differential diagnosis in histology includes other causes of megacolon, such as chronic idiopathic intestinal pseudo-obstruction or Chagas disease. However, the absence of ganglion cells is a distinguishing feature of Hirschsprung disease.
Treatment
The definitive treatment for Hirschsprung disease is surgical resection of the aganglionic segment. Pull-through procedures are commonly performed, where the normal ganglionated bowel is pulled through to the anus.
Prognosis
With early diagnosis and appropriate surgical intervention, the prognosis for Hirschsprung disease is generally good. However, some patients may experience complications such as enterocolitis or post-surgical bowel dysfunction.
Conclusion
Hirschsprung disease is a significant developmental disorder with distinctive histological features. The absence of ganglion cells in the submucosal and myenteric plexuses is critical for diagnosis. Understanding the histological and clinical aspects of this disease is essential for effective management and improved patient outcomes.
