A rich network of S100+/tropomyosin receptor kinase A+ nerve fibers in the connective tissue wall of radicular cysts: An immunohistochemical study of biopsy cases

Introduction: Limited information is available regarding the presence of nerve fibres in human radicular granulomas and cysts. The aim of the present study was to map the neural network of human radicular cysts by the immunohistochemical expression of S100 protein, tropomyosin receptor kinase A (TrkA), and p75 neurotrophin receptor (p75NTR). Material and Methods: Immunohistochemistry for S100 protein, TrkA, and p75NTR was performed on formalin-fixed and paraffin-embedded tissue sections of 16 cases. Positive structures were recorded in the wall of the cysts, arbitrarily divided into an outer layer adjacent to the jawbone and an inner layer, between the outer layer and the lining epithelium. Results: In the outer layer, a rich network was observed consisting mostly of nerve bundles that were S100-positive (16/16 cases) and TrkA-positive (13/16 cases) and thin fibres, S100-positive (8/16 cases) and TrkA-positive (7/16). In the inner layer, only S100-positive thin fibres were present. TrkA positivity was evident in the epithelial basement membrane zone. Conclusions: Human radicular cysts exhibit a dense peripheral neural network of S100-and TrkA-positive nerve fibres, consistent with Aδ and C fibers, and S100-positive fibres within the subepithelial connective tissue, primarily in association with blood vessels.