Anatomy and Physiology
The temporal (mastoid) bone sits at the back of the ear and is composed of 4 portions
- The petrous temporal bone
- The squamous temporal bone (mastoid)
- The styloid process
- The tympanic ring
The mastoid air cells exist within the squamous and petrous temporal bone. There is variation in the pneumatisation (aeration) of these air cells but they are in continuity with the middle ear via a connection called the aditus ad antrum. Within the mastoid the facial nerve runs a course firstly in the middle ear then descending down in the mastoid to exit in the stylomastoid foramen and then to enter into the parotid gland.
The mastoid air cells not only run close to the facial nerve but are also intimate with a thin plate of bone superiorly (tegmen) that abuts the meninges and posteriorly bone overlying the sigmoid sinus that drains into the internal jugular vein.
This operation is performed typically for chronic ear disease in the form of Cholesteatoma or Non cholesteatoma Chronic Suppurative Otitis Media. Occasionally it is performed in addition to a myringoplasty .
Cholesteatoma is a condition where a piece of skin from the tympanic membrane encroaches into the middle ear. The skin sac finds it difficult to self cleanse like the normal ear canal skin and infections recur. The skin sac extends into the space of the middle ear and then into the mastoid air cells as it grows.
Surgery to remove a cholesteatoma follows this skin sac to remove every piece of it so as not to allow a recurrence. There are two types of approaches:
- Canal Up – Where the ear canal is left intact
- Canal down – Where the mastoid is left in continuity with the ear canal.
A mastoidectomy operation has varying degrees of difficulty depending on the disease process. There are risks of a change in the level of hearing, balance alteration, facial nerve weakness (very rare), meningitis (very rare), recurrence of disease, discharge from the ear. The key is a thorough operation ridding the individual of the disease process. The patient has a head bandage that can come down the day after the operation. Typically the patient goes home the following day. A dressing is often placed in the ear canal / cavity for a few weeks and is then removed in the clinic. Often long term follow up is necessary to monitor the ear and look out for recurrence of disease.