The bone immediately behind the external ear is known as the “mastoid bone”. This bone can be felt behind the ear and is the area without hair growing from it. The mastoid bone is configured very similar to a sponge made out of bone. Since the air cells in the bony sponge need to be aerated through the Eustachian tube, any blockage of the Eustachian tube or the air tract within the mastoid bone can give rise to acute and chronic infected collections within the bone. Those collections then need to be removed in order to stop the infective process.
There is a special type of mastoid bone infection known as cholesteatoma. In this case, the bone has a problem with skin from the ear canal having grown through an eardrum perforation and into the mastoid bone. This gives rise to chronic drainage and loss of hearing.
All the types of mastoiditis are treated with an operation known as mastoidectomy. An incision is made behind the ear where the ear connects with the head. Through this incision specialized drills and a microscope are used to remove all infected material. This includes the cholesteatoma, if present. Once all the infection has been removed, the surgeon will decide whether the ear is appropriate for an ear bone reconstruction at the time of mastoidectomy. Sometimes, a “second-look” is needed four to six months later. The second-look allows the ear to heal and scar tissue to mature prior to placing the small ear bones. If they are placed too soon, then they may not heal correctly and result in some hearing loss.
Even with microscopic removal of the cholesteatoma, there is a rate of recurrence of approximately 15%. Children, in particular, have aggressive acting cholesteatomas and may indeed need further surgery to remove the cholesteatoma and improve the mastoid condition.
In aggressive mastoiditis or cholesteatoma cases, a “canal-wall-down” procedure may be needed. In this case, the natural configuration of the ear canal is removed and the mastoid is opened to the ear canal. From the outside, this is not really appreciated, but using a speculum and looking through the ear canal a physician can determine that a canal-wall-down procedure has been performed. The reason a mastoid canal-wall-down procedure is performed is to limit the space where cholesteatoma or mastoiditis could reside. Therefore, the recurrence rates are lowered.
A disadvantage of the canal-wall-down mastoidectomy is that the natural ossicular chain is usually disrupted by this operation. Thus, it is a balance between removing the underlying progressive disease and sacrificing hearing function. The hearing function can either be recreated through hearing aid usage or by an ear bone ossicular reconstruction.