Histological behavior of the vocal fold after hyaluronic acid injection.

The vocal fold is formed by tissues with abundant cells surrounded by an extracellular matrix. One of the most important components of the extracellular matrix is hyaluronic acid (HA). This study evaluated the inflammatory response of the vocal folds of rabbits submitted to local injection of Restylane HA. We performed a prospective, experimental, and controlled study in 22 New Zealand rabbits with injection in vocal fold. The 22 adult male rabbits underwent a 0.1-ml injection of Restylane HA in one vocal fold and a 0.1-ml injection of saline solution in the other vocal fold, at random. The animals were then subdivided in two distinct groups. One group was sacrificed after a 1-week follow-up and the other group after 3 months. Slides were then stained with hematoxylin-eosin (HE), Masson's trichrome, and toluidine blue. HA was found microscopically in all specimens of both groups. Using the stain (HE), it was easily distinguished. We have measured the inflammatory reaction by histopathology conducted by a pathologist. An increase in connective tissue was found surrounding the HA, and was always associated with a mild inflammatory response. The extended time of exposure did not increase the intensity of the inflammatory reaction. Tissue necrosis and foreign body inflammatory reaction were not observed in either group. The current study suggests that HA is a good alternative for a filling material of the vocal folds when treating glottal insufficiency.