This lesion is somewhat inappropriately named, as it is not exactly a tumour nor is it made of cholesterol but rather it is a three-dimensional collection of epidermal and connective tissues within the middle ear. Its significance lies in the fact that it grows independently and can be locally invasive and destructive, particularly affecting the bones of the middle ear. Bone erosion occurs mainly by pressure but release of osteolytic enzymes has been detected at the peripheral margins of the lesion. Osteolytic activity appears to be enhanced by the presence of infection. The (usually) unilateral lesion can give rise to a spectrum of problems, ranging from painless otorrhoea (discharge from the ear) through to serious central nervous system complications.
This occurs when squamous epithelium becomes trapped within the temporal bone during embryogenesis. It expands, resulting in conductive hearing loss either through obstruction of the Eustachian tube or by surrounding the ossicular chain.
Primary acquired cholesteatoma
The precise pathophysiology of these lesions is not absolutely certain but it is thought that chronic negative middle-ear pressure due to a dysfunction of the Eustachian tube causes the tympanic membrane to be 'sucked back' and retract. As this process continues, there is erosion of the lateral wall of the epitympanum (the upper portion of the tympanic cavity which contains the head of the malleus and the body of the incus), producing a slowly expanding defect. A pocket lined by squamous, non-keratinising epithelium is thus formed. The erosion often goes on, as the ball of epithelium grows, to surround the ossicles and may extend into the mastoid bone, lateral semicircular canal, middle and posterior cranial fossa.
Secondary acquired cholesteatoma
This arises as a result of insult to the tympanic membrane, such as perforation secondary to acute otitis media (AOM) or trauma, or due to surgical manipulation of the drum. Squamous epithelium may be inadvertently implanted by the insult so triggering the process of cellular growth resulting in cholesteatoma formation.
Spectrum of otitis media
Otitis media (OM) is an umbrella term for a group of complex infective and inflammatory conditions affecting the middle ear. All OM involves pathology of the middle ear and middle ear mucosa. OM is a leading cause of healthcare visits worldwide and its complications are important causes of preventable hearing loss, particularly in the developing world.
There are various subtypes of OM. These include AOM, otitis media with effusion (OME), chronic suppurative otitis media (CSOM), mastoiditis and cholesteatoma. They are generally described as discrete diseases but in reality there is a great degree of overlap between the different types. OM can be seen as a continuum/spectrum of diseases:
- AOM is acute inflammation of the middle ear and may be caused by bacteria or viruses. A subtype of AOM is acute suppurative OM, characterised by the presence of pus in the middle ear. In around 5% the eardrum perforates.
- OME is a chronic inflammatory condition without acute inflammation, which often follows a slowly resolving AOM. There is an effusion of glue-like fluid behind an intact tympanic membrane in the absence of signs and symptoms of acute inflammation.
- CSOM is long-standing suppurative middle ear inflammation, usually with a persistently perforated tympanic membrane.
- Mastoiditis is acute inflammation of the mastoid periosteum and air cells occurring when AOM infection spreads out from the middle ear.
- Cholesteatoma occurs when keratinising squamous epithelium (skin) is present in the middle ear as a result of tympanic membrane retraction.
The epidemiological data regarding this condition are somewhat scant, although it is one of the most common indications for otological surgery. Most of the studies are quite old but show a wide variety in geographical prevalence. This could reflect differences in medical practice rather than true epidemiological variation. Prevalence in Jerusalem has been quoted as being as high as 70 per 100,000 children, whereas a study of Australian Aboriginal children reported a prevalence of 50 per 100,000. One UK study suggests a genetic propensity in some families.
- Symptoms and signs vary according to the size of the cholesteatoma. Small lesions are associated with a progressive conductive hearing loss but, as the lesion grows and erodes into adjacent structures, there may be additional features such as vertigo, headache and facial nerve palsy.
- Associated infection can (rarely) manifest itself within the central nervous system (sigmoid sinus thrombosis, epidural abscess, meningitis) or as an abscess in the neck.
- There have been infrequent case reports of the cholesteatoma growing in:
- The former most commonly presents with otorrhoea (discharge) and hearing impairment. The latter may result in total deafness of the affected ear and impaired facial movement.
- This usually presents in childhood (6 months to 5 years) but may occasionally present much later, in adulthood.
- There is often no history of recurrent suppurative ear disease, previous ear surgery or tympanic membrane perforation.
- It may be an incidental finding on routine otoscopy of an asymptomatic child - a pearly white mass is seen behind an intact tympanic membrane.
- Larger lesions lead to conductive hearing loss.
- Frequent or unremitting painless otorrhoea which may be foul-smelling.
- Recurrent otitis, poorly responsive to antibiotic treatment.
- Progressive, unilateral conductive hearing loss.
- Tympanic membrane perforation (~90% of cases) or retracted tympanum.
- The only finding may be a pus-filled canal with granulation tissue.
- Congenital - cleft palate.
- Acquired - ear trauma (accidental or surgical), including insertion of grommets.
- Myringosclerosis: thickening and calcification of the tympanic membrane secondary to inflammation.
- Myospherulosis (spherulocytosis): a very rare foreign body reaction to oil-based ointments used in packing after surgery.
Following physical examination, these patients will undergo a spectrum of audiological tests:
- CT imaging is the investigation of choice if there is a need for assessment of the extent of the lesion and to assess subtle bony defects.This will guide the surgeon as to how to go ahead with surgery and to help in establishing how successful surgery is likely to be. However, patients should be advised that CT cannot always accurately predict what the operative findings will be and intraoperative 'surprises' are relatively common with this condition.
- Where there is concern about soft tissue involvement in addition to the bony erosion (eg, herniated brain, epidural abscess and sigmoid sinus thrombosis), an MRI scan may also be performed.
Medical therapy is reserved for those patients who refuse surgery or for whom a general anaesthetic would be too dangerous owing to comorbidity. In these patients, regular ear cleaning with treatment of infections (topical ± systemic antibiotics) is advised but, ultimately, this will not prevent cholesteatoma growth with its consequences.
The aim of surgery is to remove the cholesteatoma. Surgery involves a general anaesthetic and an incision behind the ear and in the auditory meatus. There will be a dressing applied which, depending on local practice, may be removed by the patient or the team - patients will be advised. Follow-up is any time between a day and three weeks after surgery depending on each individual surgeon's techniques and preferences. There will be a need for topical antibiotics in the first instance and possibly topical steroids later on if excessive granulation tissue forms.
There are two methods used: the open and the closed techniques; there is ongoing debate over which is ideal. Ultimately, it depends on individual patient circumstances and, sometimes, a decision cannot made until the operation has started.
- Open technique (tympanomastoidectomy): this is a longer and more involved procedure that entails removal of a number of structures postoperatively. This is the more successful of the two types of procedure in terms of cholesteatoma removal and therefore a single procedure is usually sufficient. Its drawbacks are that there is a resultant enlarged auditory meatus (at least to twice it normal size) making hearing aids difficult to fit and occasionally resulting in dizziness on exposure to cold water or air. There is a need for annual or biannual auditory canal cleaning too.
- Closed technique (tympanoplasty): this method is associated with a better end result with regards to cosmetic appearance but, as it is associated with a higher risk of persistent or recurrent cholesteatomas, a second-look operation 6-12 months down the line is mandatory. There have been promising developments in the role of specialised MRI imaging replacing the traditional second-look surgery.
- The use of otoendoscopy is being investigated.
The aims of surgery are:
- To eliminate the cholesteatoma and its associated complications.
- To enable all the usual activities of daily living, including swimming.
- To conserve residual hearing ± improve hearing if possible.
- To reconstruct the ear in a manner that reduces the chances of recurrence.
A cholesteatoma left in situ will inevitably grow. The complications depend on which structures it grows and erodes into. Thus, the patient develops a progressive conductive deafness and then may go on to have problems with dizziness, facial nerve palsy, central nervous system problems (through a mass effect or as a consequence of abscess formation) and so on.
All but the first of the complications listed below are rare (of the order of about 1% or less).
- Temporary (few months) alteration of taste.
- Ear canal stenosis.
- Facial nerve injury.
- Formation of a fistula into one of the semicircular canals.
- Labyrinthine or middle-ear injury leading to long-term dizziness.
- Acquired cholesteatoma following surgery for congenital cholesteatoma has been reported.
Surgical removal of a cholesteatoma is usually complete, although this may take more than one procedure (in no more than 5% of the patients who have had the open technique used and in 20-40% of those who have had the closed technique). Death from intracranial complications is now rare, due to earlier recognition, effective surgical treatment and control of infection with antibiotics. Life-long follow-up is required, as cholesteatomas may recur, especially congenital ones. Regular facial nerve monitoring is gradually being replaced by testing for selected cases only (eg, revision surgery, previous facial nerve weakness). Cholesteatoma remains an important cause of permanent, moderate conductive hearing loss.
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