Cholesteatoma of the middle ear is a cystic structure formed by keratinized squamous epithelium within the middle ear, often containing white, desquamated epithelial debris. Based on its origin, cholesteatomas can be classified into congenital cholesteatoma and acquired cholesteatoma.
Congenital cholesteatoma develops from ectodermal tissue remnants trapped within the temporal bone during embryogenesis, forming isolated cysts in areas such as the petrous apex, tympanic cavity, or mastoid.
Acquired cholesteatoma arises from the invagination of tympanic membrane or external auditory canal epithelium into the tympanic cavity, often associated with infections. Acquired cholesteatomas are further divided into primary acquired cholesteatoma and secondary acquired cholesteatoma.
Primary acquired cholesteatoma forms when a retraction pocket develops in the tympanic membrane before infection occurs. Secondary acquired cholesteatoma results from inflammation, such as when epithelial tissue from the margin of a tympanic membrane perforation invades the tympanic cavity, though this type is relatively rare in clinical practice.
Pathogenesis
The main theories regarding the pathogenesis of acquired middle ear cholesteatoma include:
- Retraction pocket theory
- Epithelial migration theory
- Squamous metaplasia theory
- Basal cell hyperproliferation theory
Retraction pocket theory
Dysfunction of the Eustachian tube leads to negative pressure in the tympanic cavity, causing retraction of the pars tensa of the tympanic membrane. Adhesions form, creating a retraction pocket that invaginates into the epitympanum and mastoid, resulting in adhesive cholesteatoma. Adhesion sites are often found in the posterosuperior part of the tympanic membrane but can also involve the entire pars tensa.
Recurrent inflammation causes thickening and adhesion in the mucosa, folds, and ligamentous tissues of the tympanic isthmus located between the mesotympanum and epitympanum. Obstruction of the anterior and posterior tympanic isthmus or the Eustachian tube recess leads to negative pressure in the epitympanum and mastoid, resulting in retraction of the pars flaccida and the formation of an epitympanic cholesteatoma. This is the most common type of primary acquired middle ear cholesteatoma, although adhesive cholesteatomas are also frequently observed.
Epithelial migration theory
Squamous epithelium from the margin of a tympanic membrane perforation migrates into the tympanic cavity, forming a cholesteatoma.
Squamous metaplasia theory
Inflammatory stimulation causes metaplasia of the tympanic cavity mucosa into keratinized squamous epithelium, leading to cholesteatoma formation.
Basal cell hyperproliferation theory
The epithelium of the deep external auditory canal and tympanic membrane has high proliferative capacity. Under inflammatory stimulation, hyperproliferation of epithelial cells leads to the formation of a cholesteatoma.
Pathology
The cholesteatoma matrix forms the cyst wall, with its inner layer composed of keratinized squamous epithelium. The cyst is filled with desquamated epithelium and cholesterol crystals. The keratinized squamous epithelium of the cholesteatoma is thinner than normal skin and lacks hair follicles, sebaceous glands, and the subcutaneous papillary layer. The outer layer of the cyst wall often shows inflammatory cell infiltration and capillary proliferation. During active inflammation, cellular infiltration increases, and granulation tissue proliferates. Cholesteatomas can destroy surrounding bone structures through pressure-induced bone resorption.
The mechanisms of bone destruction are believed to involve the following factors:
- Subepithelial granulation tissue containing monocytes and macrophages that resorb bone
- Granulation tissue producing collagenase and acid phosphatase, which contribute to osteolysis
- Ischemia caused by pressure, leading to bone resorption
- Lipid acids produced by the decomposition of desquamated epithelium within the infected cholesteatoma matrix, which have osteolytic effects
Clinical manifestations
When symptoms are present, they are similar to those of chronic suppurative otitis media, including ear discharge and hearing loss, but are often accompanied by headache, ear pain, and other symptoms. As the disease progresses, vertigo, facial nerve paralysis, and other intracranial or extracranial symptoms may occur.
The desquamated epithelium is often infected by anaerobic bacteria, producing a foul-smelling discharge. Severe inflammation and granulation tissue growth may result in bloody secretions.
The severity of conductive hearing loss depends on the involvement of the ossicular chain and the condition of the tympanic membrane. In some cases, the damaged ossicular chain may be replaced by cholesteatoma tissue, restoring hearing to near-normal levels. If the inner ear is affected by inflammation, bone conduction thresholds may rise, and tinnitus may occur.
Destruction of the bony labyrinth wall may lead to labyrinthine fistula, causing vertigo when pressure changes occur in the ear canal (positive fistula test). Labyrinthitis caused by bacterial toxins can also result in vertigo.
Facial nerve paralysis may occur due to compression of the facial nerve by the cholesteatoma or infection involving the facial nerve. Early-stage facial nerve decompression surgery often yields a good prognosis.
Although the incidence of intracranial complications has significantly decreased with the widespread use of antibiotics, they still occur and require attention.
Figure 1 Cholesteatoma of the right middle ear
Diagnosis of middle ear cholesteatoma can generally be established based on examination of the tympanic membrane and tympanic cavity, especially in microscopy, which is critical for observation. After clearing purulent secretions and crusts, the entrance of a retraction pocket in the pars flaccida or retraction in the posterosuperior part of the pars tensa may be visible, along with white desquamated epithelium inside the pocket. If polypoid granulation tissue is present in the external auditory canal, cholesteatoma is often found deeper within.
Pure tone audiometry typically shows conductive hearing loss, but mixed or sensorineural hearing loss may occur if labyrinthitis is present.
Temporal bone CT reveals bony destruction in the epitympanum, mastoid antrum, and mastoid area, with dense, well-defined margins. CT can assess the degree of mastoid pneumatization, the extent of the lesion, ossicular destruction, facial nerve canal condition, presence of labyrinthine fistula, jugular bulb height, and more. For evaluating mastoid cholesteatoma and intracranial or extracranial complications, MRI with different sequences is required, providing valuable information for surgical planning.
Diagnosis
Diagnosis is based on symptoms and examinations. Middle ear cholesteatoma must be differentiated from chronic suppurative otitis media and malignant tumors of the middle ear. In some cases, these conditions may coexist with cholesteatoma. Malignant tumors are characterized by more severe ear pain, early bony destruction with poorly defined margins, and irregular granulation tissue. If necessary, pathological examination is required for differentiation.
Treatment
Surgical treatment should be performed as early as possible. The principles of surgical management for middle ear cholesteatoma include:
- Complete removal of the cholesteatoma
- Preservation and improvement of auditory function whenever possible
- Maintenance of the physiological structure and function of the external auditory canal as much as possible
Middle ear cholesteatoma surgery is an elective procedure. Preoperative preparation typically involves 1 - 2 weeks of local treatment in the outpatient setting. Under a microscope, epithelial debris at the entrance of the retraction pocket is suctioned out, and granulation tissue is removed to ensure adequate drainage and control of local inflammation. This preparation can reduce surgical difficulty and improve outcomes.
Preservation and improvement of hearing is a fundamental goal. If the hearing in the contralateral ear is normal or at a functional level, efforts should be made to improve hearing while removing the lesion. When surgery is required on both ears, the ear with poorer hearing is usually operated on first. If the ear to be operated on has better hearing, especially when the contralateral ear is completely hearing loss, or if it is the only hearing ear, extreme caution is necessary, with priority given to preserving existing hearing.
Since middle ear cholesteatoma often involves mastoid management, the basic surgical techniques include canal wall-up tympanoplasty and canal wall-down tympanoplasty, as well as other derived methods. In recent years, the development of endoscopic techniques has also enabled the gradual adoption of endoscopic cholesteatoma surgeries.
Canal wall-up tympanoplasty
This technique involves removing the lesion while preserving the bony posterior wall of the external auditory canal, followed by ossicular chain reconstruction and tympanic membrane repair. The approach includes opening the posterior tympanic cavity via the facial recess, exposing the epitympanum, and extending forward into the supratubal recess. The skin of the external auditory canal and the full thickness of the tympanic membrane are elevated from the ear canal, and the cholesteatoma is completely removed up to the retraction pocket. The residual edge of the retraction pocket is trimmed and everted into the external auditory canal. Depending on the extent of the lesion, the incus and malleus head may be removed, while the tensor tympani tendon is preserved if possible. After ossicular chain reconstruction, cortical bone or cartilage is used to repair the defect in the outer wall of the epitympanum, and the tympanic membrane is repaired using an underlay or inlay technique with the temporalis fascia.
This technique has a relatively high recurrence rate and requires strict adherence to indications:
- Cases with epitympanic cholesteatoma where the bony wall of the external auditory canal is not severely damaged and adhesive cholesteatoma should be approached with caution
- Complete removal of the cholesteatoma matrix during surgery
- Well-developed mastoid air cells
- Pediatric patients, as their external auditory canal and temporal bone are still developing, making this technique preferable
- Staged surgery, where patients who can undergo regular postoperative follow-ups and are prepared for a second surgery if necessary
- Surgeons with sufficient experience and skills in otologic microsurgery
Canal wall-down tympanoplasty
This technique has the advantages of providing maximum exposure of middle ear structures, facilitating lesion removal, reducing cholesteatoma recurrence rates, and achieving satisfactory hearing outcomes. However, it leaves a large mastoid cavity, which is prone to postoperative infections, requires regular cavity cleaning, and may hinder the use of hearing aids.
Indications include:
- Severe destruction of the bony wall of the external auditory canal
- Low-lying tegmen tympani or anteriorly positioned sigmoid sinus
- Presence of intracranial or extracranial complications
- Patients unable to undergo regular follow-ups or multiple surgeries for various reasons
Canal wall-down tympanoplasty with mastoid cavity obliteration
This technique involves filling the mastoid cavity to reduce its size after completing a canal wall-down tympanoplasty. Autologous materials, such as cortical bone chips, bone dust, U-shaped myoperiosteal flaps, Palva flaps, and auricular cartilage, are commonly used for obliteration. Cortical bone chips and bone dust are mixed with fibrin glue and used to fill the mastoid cavity, up to the level of the tympanic annulus, slightly above the horizontal segment of the facial nerve canal. This ensures the normal depth of the tympanic cavity postoperatively. A vascularized tissue flap is placed over the filling material to effectively prevent infection.