Effect of mastoid cavity modification on middle ear sound transmission

The modified radical mastoidectomy and intact canal wall mastoidectomy are the two most popular procedures used today for the treatment of chronic middle ear and mastoid disease. Their effects on the anatomy of the middle ear and mastoid cavity are quite different and it might also be expected that they would modify middle ear sound transmission in different ways. This paper describes experiments with human temporal bones and a middle ear computer analog model that attempt to define acoustic differences produced by cavity modifications in these two procedures. The temporal bone studies showed that blocking the aditus (as in modified radical mastoidectomy) produced improved sound transmission in the 1,500- to 4,000-Hz range and decreased transmission below 1,000 Hz when compared to the enlarged aditus and enlarged mastoid condition (as in intact canal wall mastoidectomy). Computer model showed better transmission at all frequencies with the intact canal wall mastoidectomy simulation.