Evidence of Innervation in Talc-Induced Pleural Adhesions: Recommendation

Evidence of Innervation in Talc-Induced Pleural Adhesions: RecommendationThese findings concur essentially with those of previous studies addressing this issue, since new blood vessel formation has been reported in human and animal pleural adhesions, as well as in human and animal peritoneal adhesions. In any event, the pivotal role of angiogenesis in the production of pleurodesis was clearly demonstrated by Guo et al who, by inhibiting angiogenesis with anti-vascular endothelial growth factor antibody, reported a significant reduction in the pleurodesis score in a rabbit model.
On histopathologic analysis, all the newly formed vessels observed in the present study showed a normal histologic pattern, and morphologic abnormalities previously described in peritoneal adhe-sions, such as medial and adventitial wall thickening, were not found. However, to our knowledge, this is the first report to demonstrate lymphatic vessel growth above visceral pleura elastic lamina following talc pleurodesis. Although the role of lymphangiogenesis in adhesion formation remains unknown, it has been pointed out that visceral pleura lymphangiogenesis above the elastic lamina may either contribute to pleural drainage during pathologic states or serve to recruit cellular effectors to sites of tissue inflammation. Likewise, it is interesting to note that most arterioles observed in the present study were spatially associated with nerve fibers, thus supporting similar findings obtained in human and murine peritoneal adhesions. It has been suggested that this association is a consequence of the control role played by the angiogenic process in nerve growth during adhesion formation.
Overall, our findings provide evidence that restoration of the interrupted pleural tissue continuity resembles a regeneration, rather than a wound healing, process. Indeed, pleural repair after talc instillation is not based on the formation of a prototypical granulation tissue, since the repair process here observed was defective in the dense network of enlarged vessels. Furthermore, the initial fibroblast invasion of the fibrinous bridges ends in the organization of well-vascularized and innervated connective tissue that resembles that of the undamaged pleura. Therefore, pleural adhesion is not just a scar produced as a consequence of the repair process, but a structure establishing a functional continuity between both visceral and parietal pleura.
In conclusion, the present study demonstrates that as early as 1 week after instillation, talc-induced pleural adhesions are fibrovascular bands containing well-developed blood and lymphatic vessels more resembling newly formed pleural tissue than a simple scar. Likewise, this study shows for the first time the presence of nerve fibers within pleural adhesions, thereby suggesting that these adhesions are potentially capable of conducting pain stimuli. Further studies are required to confirm our results in human pleural adhesions.

This entry was posted in Pulmonary Function and tagged adhesion, innervation, lymphangiogenesis, neovascularization, pleurodesis, talc, ultrastructure.