Introduction and Aim In about 20-25% of appendicectomies performed for clinically suspected acute appendicitis, definite morphological changes are lacking on histopathological examination. The present study was done to investigate whether any changes in neurons and mast cells could be detected in patients presenting with clinical acute appendicitis but found to have normal appendix at histopathology. Methods A descriptive study was conducted on 50 appendix specimens which were categorized as histology-positive acute appendicitis (HPAA), clinically acute appendicitis but histologically negative (HNAA), appendices resected for other causes and appendices from forensic autopsy. A morphometric and quantitative evaluation of nerve fibers and ganglion plexus and its relation to mast cell density were studied. All sections were subjected to hematoxylin and eosin stain, toluidine blue stain, S 100 protein and neuron specific enolase (NSE) immuostaining and a quantitative image analysis system. Results Mucosal and submucosal neuronal components highlighted by NSE and S100 immunostaining observed in cases of HNAA were comparable to cases of HPAA. With S 100 immunostaining in HNAA cases, the increase in number and size of myentric neuronal plexus were mild in 40% (10/25) cases, moderate in 40% (10/25) and marked in 20% (5/25) cases as compared to 66.7% (10/15) cases of HPAA showing moderate and 33.3% (5/15) cases showing marked increase (p = 0.018). The mean mast cell count was highest in the HNAA cases (2.74) in all the four layers as compared to the HPAA (1.85) and control group (2.05). There was no difference in the relationship of the size of ganglion cells and the mast cell concentration. Conclusions Neuronal hypertrophy and mast cells may play a role in the pathogenesis of appendicitis-like pain in patients with histologically normal appendices.
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