The initial signs of a cholesteatoma are drainage from the ear canal and hearing loss.
A cholesteatoma is a benign growth of skin in an abnormal location such as the middle ear or petrous apex. The latter is an area of bone located deep to the inner ear. Normally, squamous epithelium or skin lines the entire ear canal and the outer surface of the eardrum. The outermost layer of skin is actually composed of dead cells which are constantly being sloughed off and expelled with earwax. A major component of these dead cells is a protein called keratin.
A cholesteatoma can form in the middle ear in three ways:
- A perforation of the eardrum occuring because of a chronic infection or direct trauma can lead to a cholesteatoma. The skin over the outer surface of the eardrum can start to grow through the perforation and into the middle ear.
- Some patients are born with small remnants of skin which become entrapped within the middle ear (congenital cholesteatoma) or petrous apex (petrous apex epidermoid).
- The third mechanism which his most common involves an improperly functioning eustachian tube. The eustachian tube is a canal which connects the middle ear to the back of the nose. It is responsible for equilibrating middle ear pressure to the pressure in the external environment. This tube is normally collapsed in its resting state and when we swallow or yawn, the muscles around the tube contract and cause the tube to open allowing the influx of air into the middle ear space. When this tube does not work appropriately, a relative negative middle ear pressure is generated and maintained. Over time the intact eardrum begins to retract back toward the inner ear. Eventually a skin-lined sac forms which continues to grow and cause infection and bony destruction. The problem occurs when the dead cells accumulate in the middle ear and can not be expelled. Typically an infection occurs with intermittent drainage from the ear. As this ball of dead cells acumulates it produces enzymes which cause the destruction of bone.
Complications from untreated cholesteatoma:
Erosion of the ossicles or bones behind the eardrum can lead to a conductive hearing loss. The bone over the facial nerve can also be destroyed and a facial paralysis can result. The inner ear is composed of a bony labyrinth which can also be partially destroyed. This can lead to a sensorineural hearing loss and dizziness. The infection can also spread into the veins carrying blood from the brain to the heart. This large vein called the lateral venous sinus can obstruct and cause excessive fluid to accumulate within and around the brain leading to a condition called hydrocephalus. The infection can also spread to the covering of the brain and cause meningitis. In rare circumstances, a brain abscess can result.
Tests which are oftentimes helpful include an audiogram and a CT scan of the temporal bone. An audiogram is a hearing test conducted in a sound proof room by an experienced audiologist. There the ability to hear various frequencies can be checked. How loud the various frequencies have to be before you hear them is determined. The audiologist will typically check the hearing through the air, using the eardrum, bones behind the eardrum or ossicles, inner ear and hearing, cochlear nerve and central auditory pathways. This is usually compared to the hearing obtained through the mastoid bone or bony prominence behind the ear. The latter checks the hearing attained by directly stimulating the inner ear thereby bypassing the ear canal, eardrum and ossicles. This is also referred to as sensorineural hearing.
The difference between the hearing through the air and bone is called conductive hearing.
A CT scan is a special X-ray which is taken with the patient lying down and wheeled into a large doughnut-shaped machine. Images are obtained of the temporal bone which is the bone which houses the hearing and balance mechanism. A regular CT scan of the head is not sufficient to clearly see the minute structures within the temporal bone. A detailed study with thin sections through the temporal bone is required. CT scans and all other imaging techniques allow us to get a gross idea of what might be going on in the middle ear and mastoid. These scans are the equivalent of shining light onto an object and trying to make out what the object is by studying the shadows made by it. Consequently these scans are not absolute in telling us all we want to know. Normally the middle ear and mastoid should appear black on a CT scan. Gray-colored areas may represent fluid, infection, cholesteatoma or scar from previous surgery.
If the the sac is relatively small and the ear can be kept without infection, and the hearing remains at an acceptable level, the keratin may be cleaned out in the office under microscopic examination at periodic intervals. In all other circumstances, surgery is required to help prevent the progression of infection.
The primary goal of surgery for cholesteatoma is treating the infection. The secondary goal is to restore hearing. As previously stated, an uncontrolled infection in this area can lead to complications.
In all circumstances, surgery involves general anesthesia and the procedure can last anywhere from one hour to three hours depending on the size of the cholesteatoma and extent of infection. The delicate procedure is performed using a high powered microscope. Patients typically go home either the same day after surgery or the next day depending on how they respond to general anesthesia. There are temporary restrictions following surgery which include restraining from heavy lifting, straining, nose blowing and sneezing with the mouth open only. Patients are typically seen weekly until all ear canal packing is removed.
Whenever surgery is performed for cholesteatoma, there are three possible results of surgery depending on what is found during the operation. If the cholesteatoma is small and can be removed entirely in one piece, the eardrum and the ossicles are reconstructed all in one operation.
If the cholesteatoma can be removed only in pieces, there is always a chance cholesteatoma fragments left behind may regrow at a later time. In this case it is our preference to come back several months later to remove any fragments which may have grown when they may be a favorable size for total excision. We would also delay ossicular reconstruction until the second operation.
If the cholesteatoma is rather extensive and adherent to the inner ear or facial nerve, it may not be possible to remove the entire cholesteatoma and a radical mastoidectomy is performed. The portion of the cholesteatoma that is adherent to the inner ear and/or facial nerve is left. In this case a situation is created where the keratin accumulation can be safely removed in the office. The bony partition between the back part of the ear canal and the mastoid bone is removed. The eardrum, malleus and incus are removed in order to allow exposure of the inner ear and facial nerve for cleaning in the office. The opening to the ear canal is also enlarged. In this case periodic cleaning of this mastoid cavity every 3-6 months is essential.
Surgery can be performed either through the ear canal or in combination with an incision behind the ear.
With a cholesteatoma limited to the tympanic membrane or with a small congenital cholesteatoma or with a limited cholesteatoma forming through an eardrum perforation, the procedure can be done through the ear canal. Incisions are made within the ear canal and the ear canal skin along with the eardrum are lifted to inspect the middle ear.
Frequently the chorda tympani nerve (taste nerve) may need to be moved aside to allow adequate inspection. This may cause a temporary taste disturbance from the front part of the tongue on that side. If the nerve becomes overly stretched, the patient can have a permanent metallic taste. In order to avoid this the nerve is divided. Eventually the taste buds on that side usually become reinnervated from taste fibers from the opposite side of the tongue. Occasionally the cholesteatoma may invade this nerve and it may be necessary to resect the nerve anyway.
In order to allow clear visualization of the cholesteatoma, frequently it is necessary to remove the incus bone. Inner ear trauma leading to temporary dysquilibrium from overmanipulation of the stapes bone while dissecting the cholesteatoma from the surrounding structures can occur. Removal of the incus bone helps prevent inner ear trauma.
The cholesteatoma and/or retracted porrtion of the eardrum is then dissected and removed. The eardrum is repaired using the covering (fascia) of the chewing muscle (temporalis) as a template for tympanic membrane growth. The continuity of the ossicles is then restored using either the patient’s own incus or an artificial prosthesis.
Frequently the mastoid bone located behind the ear must be explored to remove any cholesteatoma that may have spread there through the middle ear. Another reason to perform a mastoidectomy is to improve ventilation of the middle ear. This can be done in addition to the tympanoplasty as described above. Whether the bony partition between the external ear canal and mastoid is removed or not depends on the extent of disease. Canal-wall-down refers to the removal of this bony partition. Canal-wall-up refers to keeping this bony partition intact. The term modified radical mastoidectomy refers to an operation where this bony partition is removed and the eardrum and ossicles are reconstructed. A radical mastoidectomy is an operation where this bony partition is removed and the eardrum, malleus and incus bones are permanently removed so that the inner lining of the large cholesteatoma sac can be safely cleaned in the office. This operation is done when an extensive cholesteatoma is encountered or one that is adherent to the inner ear or facial nerve.
Experienced surgeons can usually perform this type of surgery in about two hours.
Consequences & Risks of Surgery:
Numbness of the external ear is a natural consequence of an incision behind the ear. Some sensation returns several months later but return is usually incomplete. Most patients do not find this troublesome. Shortly after surgery the ear may protrude slightly. The ear almost always returns to normal as the wound behind the ear heals.
Risks of the surgery include taste disturbance, facial paralysis, recurrence of cholesteatoma, hearing loss and dysequilibrium.
Temporary taste disturbance as previously discussed can be a consequence of chorda tympani nerve (taste nerve) injury.
The facial nerve courses through the middle ear on its way to the muscles of the face. Paralysis of the face can occur after ear surgery but is extremely uncommon. There is a general feeling that surgeons who are fellowship trained in otology/neurotology and those who perform ear surgery exclusively have a reduced incidence of facial nerve injury.
Temporary dysequilibrium can occur from dissection of the cholesteatoma from surrounding structures such as the inner ear and stapes bone.
Even after having surgery, cholesteatoma can recur. For this reason patients who have had a cholesteatoma surgically treated and especially those who have had a canal-wall-down procedure require close follow-up to detect early recurrence.