Identify the lateral semi-circular canal

Several drilling techniques are required to clear pneumatised bone from the sinodural angle, over the antrum, and into the epitympanum and its lateral extension. As you drill anteriorly towards the epitympanum and find that the drill is too large for the task, change to a burr that will fit easily into this space.

In the superior part of the region you can use a large sized burr because you are not likely to damage the vital structures particularly in the air filled space. The orientation of the drilling should be changed in the sino-dural angle. It has no vital structures.

In the region between the tegmen and the external ear canal use a burr that is large enough to occupy the space between them. Apply the drill first at the level of the antrum and use its shoulder to remove the bone with an outward sweeping action.