The middle ear lies behind the eardrum and is separated from the inner ear by the round and oval window. This area is somewhat shaped like a box with six walls. It contains the auditory ossicles (hearing bones) that transmits vibrations from the eardrum to the hearing apparatus in the inner ear. A hollow cavity known as the eustachian tube connects the middle ear to the back of the nasopharynx thereby allowing for the air pressure to be balanced on either side of the eardrum. Sometimes a cystic mass can grow in the middle ear. This tumor is known as a cholesteatoma, and despite its name, it is not always or entirely composed of cholesterol and neither is it cancerous.
What is a cholesteatoma?
A cholesteatoma, also referred to as a keratoma, is an abnormal growth of skin cells that is trapped in the middle ear. Apart from the danger associated with this expanding mass in the confined space of the middle ear, cholesteatomas contain enzymes which can also erode the surrounding skull bone and the damage can extend into the inner ear. Cholesteatomas may be congenital (present from birth) or acquired. It is a serious complication of chronic otitis media (middle ear infection). Surgical removal of the cholesteatoma is essential and if left untreated, it can lead to deafness, facial nerve palsy, meningitis or complicate into a brain abscess which is potentially fatal.
How does a cholesteatoma develop?
Squamous epithelium lines the outer ear canal and encroaches onto the lateral aspect (outer surface) of the eardrum but is largely absent in the middle ear. This epithelium makes up the epidermis of the skin surface and becomes highly keratinized to form an impermeable barrier that is shed on a daily basis. These cells are ‘sucked’ into the middle ear and form nests that are covered by keratinized squamous epithelium or the same mucus-secreting epithelium of the middle ear. It may also have small collections of cholesterol along with other debris within it. The cysts are usually 1 to 4 centimeters in diameter.
Causes of a Cholesteatoma
The causes of a cholesteatoma varies depending on whether it is congenital or acquired. With regards to acquired, it may be either primary or secondary.
Squamous epithelial cells may enter the middle ear during fetal development and develops into a cholesteatoma. It only becomes apparent later anywhere around the age of 6 months to 5 years. It is often missed in the early stages because unlike an acquired cholesteatoma, the eardrum is usually not perforated. The mass grows over time, obstructs the eustachian tube and disrupts the ossicles thereby leading to conductive hearing loss which is the often the first and sometimes only symptom that is seen.
Chronic allergic and infectious rhinitis, sinusitis and otitis media disrupts the function of the eustachian tube. Swelling of its walls blocks the tubular cavity and air pressure cannot be equalized on either side of the eardrum. A negative pressure (vacuum) develops within the middle ear and this causes the eardrum to retract. The eardrum along with epithelial cells are then ‘sucked’ into the middle ear as a pouch or sac. Over a period of time it develops further to form the typical cholesteatoma. This is known as a primary acquired cholesteatoma.
Another class of acquired cholesteatoma is the secondary acquired cholesteatoma which develops as a result of a perforation of the eardrum. This may arise with otitis media, trauma, insertion of grommets (tympanostomy tubes) or during surgery. Epithelial cells can then enter the middle ear and develop into a cholesteatoma.
A cholesteatoma will not develop in every one of the causes above but is more likely to occur in the chronic setting particularly when the causative condition is left untreated.
Signs and Symptoms
The typical signs and symptoms of a cholesteatoma includes :
- Ear discharge (otorrhea) which is usually foul smelling.
- Feeling of fullness or pressure in the ear but not pain (painless).
- Hearing loss ranging from partial to complete (unilateral).
- Perforated eardrum.
However, the clinical presentation is at times not typical and it is not uncommon for only one or even none of these symptoms to be present and may only develop later as the condition progresses. In a congenital cholesteatoma in particular, ear discharge is absent since the eardrum is not perforated.
Dizziness is not a common clinical feature but may be present. Cholesteatomas are prone to infection which is often persistent and difficult to treat. Therefore the presentation may include the symptoms of otitis media. In these cases fever, ear pain, poor balance and irritability in children may be noticed.
Complications of a Cholesteatoma
Apart from the damage to the ossicles and subsequent conductive hearing loss, a cholesteatoma may also lead to various other complications which may also be diagnosed. These complications arise as the cholesteatoma grows, compresses surrounding structures and erodes the bony walls of the middle ear thereby infiltrating the skull. Complications may include :
- Facial paralysis
- Brain abscess
The clinical features should prompt further diagnostic investigation by the means of radiographic imaging. A CT scan and/or MRI is usually sufficient to diagnose a cholesteatoma along with the clinical findings and medical history. Audiometry to assess hearing loss is advisable and may also serve as a means of evaluating the effectiveness of surgery and subsequent management.
What does it mean to have a cholesteatoma?
Many patients do not realize the serious nature of a cholesteatoma and are therefore hesitant to undergo surgery. A cholesteatoma means that a person has an abnormal growth in the middle ear which is gradually expanding in size and will damage the hearing apparatus of the ear, erode into the skull and lead to life-threatening complications if left unattended.
Surgery and Video
A cholesteatoma requires surgical removal but an infection first has to be treated prior to surgery in order to prevent spread of microorganisms to uninfected tissue. Depending on the degree of erosion of the ossicles, reconstruction may need to be considered either at the same time as the cholesteatoma removal or at a later stage. The eardrum (tympanic membrane) is also perforated in most cases and this also needs to be repaired. This surgical procedure (refer to video) is known as a tympanoplasty and the surgeon enters the middle ear through the ear canal.
Ossicular reconstruction is also dependent on whether the cholesteatoma can be removed as a single mass or in pieces. If removed in pieces then it is possible that some of the tissue may remain and grow again to form another cholesteatoma. In this case surgery will be needed again at a later stage to remove the new cholesteatoma and ossicular reconstruction may not be viable during the original procedure.
If the bony part of the skull known as the mastoid process has also been infected and eroded then this portion may have to be removed as well. This procedure is known as a tympanomastoidectomy. In this case, the surgeon will reach the middle ear from behind the ear. There are two variations of the mastoidectomy procedure which is known as the canal-wall-down (CWD) or canal-wall-up (CWU) mastoidectomy.
Canal-Wall-Up vs Canal-Wall-Down Mastoidectomy
In a CWD mastoidectomy, the posterior (back) wall of the ear canal is removed to make the ear canal and the mastoid a single cavity (mastoid bowl) which is exposed to the exterior environment. It is the preferred method for permanent eradication of a cholesteatoma. In a CWU mastoidectomy (also known as intact canal wall mastoidectomy), the bone that makes up the posterior wall of the outer ear canal is spared and there is no single large cavity as is the case with CWD mastoidectomy. There is a greater chance of recurrence of the cholesteatoma but allows for a normal appearance.
Recurrence of a Cholesteatoma
Cholesteatomas have a high risk of recurring if the underlying defect of the eustachian tube and other diseases contributing to it is not treated and managed effectively. There is also a chance of recurrence with incomplete removal of the cholesteatoma (residual-recurrent cholesteatoma) particularly when there is ossicular erosion. Recurrence may be is highest 3 to 6 years after surgery. Another factor for recurrence is by performing a canal-wall-up mastoidectomy when the middle ear does not have adequate natural ventilation.
1. Cholesteatoma. Emedicine
2. Cholesteatoma : Pathogenesis and Surgical Management. Department of Otolaryngology, University of Texas Medical Branch
3. Mastoidectomy. Ohio Ear Institute