Cholesteatoma is a potentially harmful cyst of skin that occurs in the middle ear, the space behind the eardrum.
Congenital cholesteatoma is thought to arise from embryologic rests of epithelium, or skin cells, which are left behind in the middle ear during development in utero. These can be difficult to detect as often patients do not have symptoms of chronic ear disease until the cyst has become quite large.
Acquired cholesteatoma typically develops as a result of eustachian tube dysfunction and chronic negative middle ear pressure. This negative pressure creates a suction effect on the ear drum. The eardrum, or tympanic membrane, is comprised of three layers, and the outer layer is made of skin. Just like skin on any other part of the body, it creates keratin, or flakes of skin. When the eardrum is subjected to chronic negative pressure, it can collapse into the middle ear and wrap around the delicate structures present there. This can result in trapping of keratin debris and cyst formation, or cholesteatoma.
Other potential causes of cholesteatoma development include traumatic implantation of skin cells into the middle ear (either through perforation or fracture of the temporal bone or from previous surgery), and metaplasia, whereby normal mucosal cells of the middle ear lining convert into cholesteatoma-forming squamous cells. These are less common mechanisms of cholesteatoma formation.
Treatment of cholesteatoma typically begins with imaging, usually a CT scan, to determine the severity of the cyst. Once a cholesteatoma has formed, surgery is necessary for removal.
Cholesteatoma surgery is particularly challenging as there are many delicate structures in the middle ear which must be protected, particularly the hearing bones; the facial nerve, which controls the muscles of the face; and the chorda tympani nerve, which carries taste sensation from the tongue. Other critical nearby structures include large blood vessels such as the carotid artery and jugular vein; the dura mater, which is the fibrous cover of the brain; and the inner ear structures responsible for hearing and balance.
In some cases, some of the middle ear structures, typically the auditory ossicles and the chorda tympani nerve, must be taken out in order to completely remove the cholesteatoma. The middle ear space is continuous with the mastoid bone, and cholesteatoma can extend into this area. Often cholesteatoma surgery includes a mastoidectomy component, in which this bone is drilled away. This procedure can allow removal of tissue which may be chronically inflamed or which may contain cholesteatoma and also give additional exposure to the middle ear.
The goals of cholesteatoma surgery are to create a safe, dry ear free from cholesteatoma and to restore or preserve hearing. In many cases, hearing can be preserved; however, if the hearing bones have been surrounded by cholesteatoma, they may need to be removed during the course of surgery. This usually results in a hearing loss that can potentially be corrected by reconstructing the hearing mechanism. This reconstruction is typically done at a later surgery; however, if the surgeon concludes that there is low risk of residual disease, it may be possible to reconstruct the hearing mechanism at the initial surgery.
Often a second surgery will be needed to explore the middle ear to be sure that no cholesteatoma remains, as even a tiny amount of residual cholesteatoma can result in a recurrence. Typically reconstruction of the hearing mechanism is performed at this time, if necessary.
Michael Cohen, M.D.