Identify the dura of mastoid region

The dura of the tegmen tympani is not smooth. It has irregularities corresponding to the gyri on the surface of the brain and it is curved. The most inferior part of the tegmen dura is at the most lateral part of the region. It curves down at the lateral extremity of the middle cranial fossa. As you extend drilling into the mastoid cavity you will notice the dura actually curves upwards and requires reorientation of the head if the equator of the burr is to be kept visible. Note that if you don’t remove that bone over the dura deep in the cavity, you will have a more limited access to structures like the incus. The space for the drill will be somewhat restrained.

The dura over the sigmoid sinus balloons out smoothly and if the equator of the burr is to be kept visible the head should be rotated towards the surgeon.

The intent of temporal bone surgery in most cases is to leave a very thin layer of cortical bone over the dura.