Thinning the external ear canal

If you drill through the bone of the external ear canal, you will find yourself of course, in the ear canal. The problem with that is, it is likely that skin will fall then into the mastoid air system, and that you can create a cholesteatoma. Also there is a risk of skin becoming completely buried in the mastoid and not then visible from observation.

If you leave a great deal of bone along the posterior aspect of the external ear canal you can be fooled into thinking that the facial nerve is in a different location to what it really is. If you inadvertently made a dissection too deep on the posterior areas near the mastoid tip you could arrive at the facial nerve before you had found two other landmarks (lateral semicircular canal and incus) that are known to be critical in terms of a safe location of this structure.