Experimental models of aural cholesteatomas in Mongolian gerbils.

Mongolian gerbils have a remarkable propensity for the development of aural cholesteatoma; canal cholesteatomas develop spontaneously in aged animals. In the present study, cholesteatomas were produced in a single species, Meriones unguiculatus, by three different methods of induction: 1) external canal ligation (ECL), 2) eustachian tube obstruction (ETO) by electrocautery, and 3) application of propylene glycol (PG) into the middle ear. Each method of induction resulted in cholesteatomas with characteristic features and success rates. With ECL, cholesteatomas could be induced in all ligated ears; stage III and IV cholesteatomas were seen in 4 of 12 ears after 8 weeks. With ETO, cholesteatomas were seen in 7 of 9 animals 8 weeks after induction. With PG, cholesteatomas developed in 2 of 7 animals 4 weeks after induction, although keratin accumulation in the external auditory canal could be found in all animals injected. Although epithelial hyperplasia of the external auditory canal was most prominent in the ECL group, it was also seen in the ETO and PG groups. Keratin accumulation in the ECL or PG group was much greater than that in the ETO group. Thickening of the tympanic membrane, which was most prominent in the PG group, was quite variable in the other groups. Adhesions of the tympanic membrane began at the prominence of the cochlea in the ECL group. In contrast, adhesions in the PG group usually began at the superior bulla, the area in which PG was applied. Each of the three methods of inducing cholesteatoma may be helpful in investigating different clinical aspects of this disease.