Suitability of Formaldehyde-Treated Acellular Dermis for Tympanic Membrane Repair in Chinchillas

Abstract

Formalin-fixed acellular dermis (AlloDerm; LifeCell Corporation, Branchberg, NJ, USA) is safe and efficacious for tympanoplasty in the chinchilla model as compared with the established technique of nonfixed acellular dermis tympanoplasty. Temporalis fascia autografts have been shown safe and effective in the treatment of near-total tympanic membrane (TM) perforations. The formalin-fixation technique first described by Perkins allows the autologous fascia graft to be shaped to more closely resemble the natural TM and has been successful but somewhat cumbersome. The use of acellular dermis as a fascia substitute has also been shown safe and effective in closing smaller perforations. We sought to determine whether formalin-fixed acellular dermis is as safe and useful as nonfixed acellular dermis for TM perforation repair by examining inflammation and tissue effects in a well-established animal model of perforation. Fifteen adult chinchillas underwent creation of 2-mm central perforations created using a Coherent CO2 laser. Each chinchilla underwent an immediate formalin-fixed acellular dermis repair in one ear and an unfixed acellular dermis repair in the other ear as a control. The chinchillas were randomized with regard to the repair applied to each ear. After 6 weeks of observation, the animals were killed by using sodium pentobarbital (dose, 150 mg/kg). The TMs were otomicroscopically examined for tissue reaction and repair success by a blinded observer. An estimate of residual perforation, if any, was made at that time. The TMs were then harvested and examined histopathologically by a blinded veterinary pathologist. Thirteen chinchillas survived to the evaluation endpoint. There were no significant differences in inflammation, fibrosis, and cellular ingrowth between the 2 groups, although there was a trend toward less inflammation in the formalin-fixed ears. Effusions were present in 15% of non-formalin-fixed ears. Adhesions were present in 15% of non-formalin-fixed ears and 8% of the formalin-fixed ears. A TM cholesteatoma was observed in one non-formalin-fixed ear. The TMs were completely healed in 11 (85%) of 13 TMs in each group. Formalin-fixed acellular dermis was as safe and efficacious as nonfixed acellular dermis in the repair of TM perforations in a chinchilla model. No adverse tissue effects related to formalin treatment were observed.