Identifying the dura

In cortical mastoidectomy, you will be thinning the bone over the dura and it’s quite possible that some dissections will expose the dura. This is usually not a problem. It’s not easy to go through the dura with a drill. You have to have the drill engaged on the dura for more than an instant in this circumstance for that to happen. You shouldn’t be overly worried when you are drilling near the dura that you will inadvertently go straight through it. This is actually very difficult to do, though worth mentioning that under some situations, the bone overlying the dura will be missing. In fact the dura may be hanging down into the mastoid cavity. Always be aware of that possibility and if there has been previous infection or inflammation in the mastoid, and previous surgery, there can be scarring between the dura and there can be fibrous tissue surrounding the dura that can present much more of a risk to the naïve surgeon who can be drilling along not recognising this.

Not being aware that there is some bone missing, and not realising the fact that the dura is immediately behind the scar tissue, the surgeon may cause a breach in the dura and therefore a CSF leak. Part of the training for the cortical mastoidectomy is to be able to identify the general direction and orientation of the dura, so that the position of this particular structure can be predicted by the surgeon and that their drilling technique will be in an orientation that will take them parallel to the structure and therefore they will be highly unlikely, even in cases of unusual pathology to inadvertently damage or cause a tear within the dura.

Repair the dura or exposure of the ear canal with a fibrous sheet of temporalis fascia supported by bone paté.