A mastoidectomy is any type of surgery that removes a portion of the mastoid bone.
The mastoid bone is a part of the temporal bone (the bone that surrounds the ear). The mastoid is situated behind the opening of the ear canal and is the lump behind the ear where the bone of the skull gives way to the muscle of the neck. The mastoid bone has a solid outer cortex (outer layer of bone), but is mostly composed of trabeculated (honey comb) bone. These trabeculae form a complex network of air containing passages that come together at the antrum, which is a bony cavity that opens into the middle ear.
Several very important structures are contained within the mastoid bone, but are usually surrounded by a layer of more solid bone. These structures include: the labyrinth (inner ear), facial nerve (the nerve that controls the muscles of facial expression), the corda tympani nerve (a nerve that supplies taste to the front two thirds of the tongue), and the sigmoid sinus (a venous blood vessel that drains blood from the brain). The temporal lobe of the brain lies immediately above the mastoid bone.
There are several reasons to do a mastoidectomy. The most common is to remove disease of the mastoid itself. Diseases of the mastoid include mastoiditis (an acute or chronic infection of the mastoid bone), and cholesteatoma (a disease of displaced skin growing and eroding bone inside of the ear). Both of these conditions are common causes of chronically ear drainage.
Another reason for a mastoidectomy is as an approach to other structures in the ear. For example, cochlear implants are inserted into the inner ear after performing a mastoidectomy. The mastoidectomy allows the surgeon to insert the cochlear implant into the inner ear at the proper angle and with good visualization.
A mastoidectomy may be needed as an approach to tumors of the middle ear or even deeper structures such as nerve tumors (acoustic neuromas or facial nerve tumors). These tumors cannot be approached and removed through the ear canal alone.
The physicians of the Ear Institute of Chicago will frequently perform mastoidectomy as part of an approach to give neurosurgeons access to parts of the brain and brainstem that otherwise would not be approachable, or not without more risks to the patient. Finally, mastoidectomy may be used as an approach to repair the facial nerve for facial paralysis, or to repair a cerebrospinal fluid fistula (a leak of the fluid that surrounds the brain).