Histopathologic Evaluation of Hyaluronic Acid and Plasma-Rich Platelet Injection into Rabbit Vocal Cords: An Experimental Study.

Objective: Various materials are used by otolaryngologists for vocal cord injections in the management of vocal cord paralysis. An ideal injection material should be long-term effective, readily available, cheap, easy to prepare, have no donor morbidity, easy to use, biocompatible, resistant to resorption or migration, and easy to extract during revision. In this study, we aimed to see the histopathological effects of hyaluronic acid (HYA) and platelet-rich plasma (PRP) injections into the vocal cords of New Zealand rabbits.

Methods: PRP was injected into the right vocal cords of twelve rabbits, which was prepared from their serum (PRP group). HYA was injected into the left vocal cords of first six rabbits (numbered 1-6) (HYA group), and the left vocal cords of the other six rabbits (numbered 7-12) were followed with no intervention (control group). Two months later, histomorphological findings in the vocal cords were assessed by two experienced pathologists in seven parameters: chronic inflammation, mucosal atrophy, necrosis, neovascularization, fibrosis, foreign body reaction, and muscular atrophy. They were scored double-blinded as negative (0), mild (+1), moderate (+2), and severe (+3). Fisher's chi-square test was used to evaluate any statistical significance among the three groups.

Results: Chronic inflammation, mucosal atrophy, necrosis, foreign body reaction, and muscular atrophy parameters were scored as "0" for each preparate by both pathologists. For neovascularization and fibrosis, a stasistically significant difference was seen among the three groups (p<0.05). Neovascularization was increased in the PRP and HYA groups compared with the control group. No significant difference was observed in fibrosis when the groups were compared separately. After two months, two of the six vocal cords injected with HYA revealed HYA; however, none of the PRP-injected vocal cords showed PRP.

Conclusion: HYA and PRP can be safely injected into vocal cords. Our findings show that HYA is a biocompatible and safe injection material for clinical use. Only two of the six vocal cords showed HYA at the end of two months, suggesting that HYA is a short-term effective material. Similarly, PRP was also shown to be a short-term effective material and can be used in patients for testing purpose before using a long-term effective material. The advantages of PRP are that it is inexpensive, readily available, and completely inert as it is prepared from the subject itself.