Cholesteatoma 

Cholesteatomas have been recognized for decades as a destructive lesion of the skull base that can erode and destroy important structures within the temporal bone. Its potential for causing central nervous system complications (eg, brain abscess, meningitis) makes it a potentially fatal lesion.

Cholesteatomas were first described in 1829 by Cruveilhier, but Muller first named them in 1858. Throughout the early half of the 20th century, cholesteatomas were managed by exteriorization. The mastoid air cells were exenterated, the posterior external auditory canal removed, and the ear canal opening into the resulting cavity enlarged to ensure adequate air exchange and to make visual inspection simple.

In the 1950s and 1960s, a new approach was promulgated by William and Howard House's Otologic Medical Group (currently the House Ear Clinic). The surgical anatomy of the facial recess was described and clarified by William House, MD, the great pioneering otologist of the 20th century. Operating through the facial recess permitted access to the middle ear through the mastoid without removing the posterior canal wall.

By operating through the facial recess, cholesteatoma could be removed without taking down the posterior canal wall. Over time, more and more surgeons attempted to leave the basic underlying anatomic structure of the ear and temporal bone intact by preserving the canal wall. These aggressive attempts to conserve the normal anatomy of the ear created great controversy. Surgeons tended to align themselves with either the old canal-wall-down or with the new canal-wall-up philosophies.

Over the last couple of decades, most otologic surgeons have migrated to an intermediate position. Most otologic surgeons in the United States now perform both techniques, selecting one or the other of these operations depending on the individual circumstances of a particular patient.

A cholesteatoma consists of squamous epithelium that is trapped within the skull base. Squamous epithelium trapped within the temporal bone, middle ear, or mastoid can expand only at the expense of the bone that surrounds and contains it. Consequently, the complications associated with a growing cholesteatoma include injury to any of the structures normally found within the temporal bone. Occasionally, cholesteatomas escape the confines of the temporal bone and skull base. Extratemporal complications may occur in the neck, central nervous system, or both. Cholesteatomas sometimes become large enough to distort normal brain and produce brain dysfunction from mass effects.

Bony erosion occurs by 2 principal mechanisms. First, pressure effects produce bony remodeling, as occurs normally throughout the entire skeleton when pressure is applied consistently over time. Second, enzymatic activity at the margin of the cholesteatoma enhances osteoclastic activity, which greatly increases the speed of bone resorption. The level of these osteolytic enzymes appears to increase when a cholesteatoma becomes infected.^[1]

Frequency

The incidence of cholesteatomas is unknown, but it is a relatively common reason for otologic surgery (approximately weekly in tertiary otologic practices). Death from intracranial complications of a cholesteatoma is now uncommon, which is attributable to earlier recognition, timely surgical intervention, and supportive antibiotic therapy. Cholesteatomas remain a relatively common cause of permanent, moderate conductive hearing loss in children and adults.

Generally, 3 separate types of cholesteatomas are identified based on different etiologies: congenital, primary acquired, and secondary acquired. The evolution of these 3 different types of cholesteatomas is described in the section below on pathophysiology.

Congenital

Congenital cholesteatomas arise as a consequence of squamous epithelium trapped within the temporal bone during embryogenesis. The typical congenital cholesteatoma is found in the anterior mesotympanum or in the perieustachian tube area. They are identified most commonly in early childhood (6 mo to 5 y).

As they expand, they can obstruct the eustachian tube and produce chronic middle ear fluid and conductive hearing loss. They can also expand posteriorly to encase the ossicular chain and, by this mechanism, produce conductive hearing loss. Unlike other forms of cholesteatoma, congenital cholesteatomas are usually identified most commonly behind an intact and normal-appearing tympanic membrane. The child often has no history of recurrent suppurative ear disease, previous otologic surgery, or tympanic membrane perforation.^[2]

Primary acquired

Primary acquired cholesteatomas arise as the result of tympanic membrane retraction. The classic primary acquired cholesteatoma develops from progressively deeper medial retraction of the pars flaccida into the epitympanum. As this process continues, the lateral wall of the epitympanum (called the scutum) is slowly eroded, producing a defect in the lateral wall of the epitympanum that slowly expands. The tympanic membrane continues retracting medially until it passes over the heads of the ossicles and into the posterior epitympanum. Ossicular destruction is common. If the cholesteatoma pokes posteriorly into the aditus ad antrum and the mastoid itself, erosion of the tegmen mastoideum, with exposure of the dura and/or erosion of the lateral semicircular canal with deafness and vertigo, may result.^[3]

A second type of primary acquired cholesteatomas arises when the posterior quadrant of the tympanic membrane is retracted into the posterior middle ear. The drum initially adheres to the long process of the incus. As retraction continues medially and posteriorly, squamous epithelium envelops the superstructure of the stapes and retracts into the sinus tympani. Primary cholesteatomas arising from the posterior tympanic membrane are likely to produce facial nerve exposure (and occasionally paralysis) and destruction of the stapedial superstructure. Surgical removal from the sinus tympani may be extremely challenging.

Secondary acquired

Secondary acquired cholesteatomas occur as a direct consequence of some type of injury to the tympanic membrane. This injury can be a perforation that has arisen as a result of acute otitis media or trauma, or it may be due to surgical manipulation of the drum. A procedure as simple as the insertion of tympanostomy tubes could implant squamous epithelium into the middle ear, ultimately producing a cholesteatoma. Posterior marginal perforations are the most likely to result in cholesteatoma formation. Although central perforations are considered unlikely to produce cholesteatomas, central perforations occasionally result in cholesteatoma formation. Any deep retraction pocket can result in cholesteatoma formation if the retraction pocket becomes deep enough to trap desquamated epithelium.^[4]

The hallmark symptom of a cholesteatoma is painless otorrhea, either unremitting or frequently recurrent. When the cholesteatoma becomes infected, the infection may be extremely difficult to eradicate. Because the cholesteatoma has no blood supply, systemic antibiotics cannot be delivered to the center of the cholesteatoma. Topical antibiotics often surround a cholesteatoma, suppress infection, and penetrate a few millimeters toward its center; however, a large, infected cholesteatoma is resistant to any type of antimicrobial therapy. Consequently, otorrhea either persists or recurs, despite frequent and aggressive treatment with antibiotics.

Hearing loss is also a common symptom of cholesteatomas. Large cholesteatomas fill the middle ear space with desquamated epithelium, with or without associated mucopurulent discharge. Ossicular damage is frequently present and can produce or magnify a conductive loss. See the images below.

Dizziness is a relatively uncommon symptom of cholesteatomas, but it does occur if bony erosion produces a labyrinthine fistula or if the cholesteatoma is lying directly on the footplate of the stapes. Dizziness is a worrisome symptom because it may presage the development of more serious complications.

Upon physical examination, the most common sign of a cholesteatoma is drainage and granulation tissue in the ear canal and middle ear unresponsive to antimicrobial therapy. A tympanic membrane perforation is present in more than 90% of cases. Congenital cholesteatomas are an exception and the drum often remains intact until the middle ear component is quite large. Occasionally, a cholesteatoma that is produced by surgical implantation of squamous epithelium manifests prior to disruption of the tympanic membrane, but even in such cases, the cholesteatoma eventually produces a tympanic membrane perforation.^[5]

Quite frequently, the only finding upon physical examination is a canal filled with mucopus and granulation tissue. Sometimes eliminating the infection and resolving the granulation tissue with either systemic antibiotics or ototopical antibiotic drops is impossible. When ototopical therapy is successful, a deep tympanic retraction pocket may be seen in the pars flaccida or posterior quadrant.

Very seldom is a cholesteatoma first identified based on one of its complications; however, this occasionally happens in children. An infection associated with the cholesteatoma can erupt through the inferior mastoid cortex and manifest as an abscess in the neck. Occasionally, cholesteatomas first manifest with the signs and symptoms of central nervous complications: sigmoid sinus thrombosis, epidural abscess, or meningitis.

Virtually all cholesteatomas should be excised. Occasional exceptions include the patient whose general health is so poor that it makes a surgical procedure too risky. Some patients who have cholesteatomas in their only hearing ear are, with good reason, reluctant to undergo surgery. The risks of profound hearing loss from surgical removal are generally less than the risk associated with leaving the cholesteatoma in situ.

The only absolute contraindications to the surgical removal of cholesteatomas are medical in nature. Some individuals have health problems of such gravity as to make the risk of surgical intervention unacceptably high.

Absence of hearing in the contralateral ear is a relative contraindication to surgery. Frequently, the cholesteatoma presents a greater risk to residual hearing than surgery, and, more often than not, surgical removal is the management option of choice even when the cholesteatoma is in the only hearing ear.