Cholesteatoma is an uncommon disease of the ear in which non-neoplastic, keratinizing squamous cell epithelium grows from the tympanic membrane or within the middle ear. Cholesteatomas consist of accumulated keratin surrounded by squamous cell epithelium. Although they are non-neoplastic, cholesteatomas have a tendency to invade into surrounding structures, leading to destructive symptoms.

Cholesteatomas can be classified as either congenital or acquired.

Congenital: Congenital cholesteatomas occur in 3 per 100 000 children. The average age of affected individuals is 6.58 years, with a predilection for boys; the male to female ratio is 3:1.

The pathophysiology of congenital cholesteatomas is poorly understood. Many theories have been postulated attempting to explain the etiology.

• Migration theory – The migration theory emphasizes the topographic location of the lesion near the tympanic isthmus. During fetal development, the tympanic annulus drives the proliferation and migration of skin from the external ear. Without a barrier between the external and middle ear, ectodermal tissue migrates and continues to proliferate within the middle ear, subsequently resulting in cholesteatoma formation.
• Amniotic fluid contamination theory – Epidermal cells present within amniotic fluid, enter the middle ear via the eustachian tube, and proliferate to form a cholesteatoma.
• Inclusion theory – Inflammation and retraction that occurs near the malleus handle and neck result in cells of the tympanic membrane inoculating the middle ear.
• Epidermoid formation theory – An epidermoid is a lesion surrounded by squamous cell epithelium. During embryogenesis, an epidermoid forms from the first pharyngeal cleft. The persistence of this epidermoid results in a cholesteatoma.

Acquired: Acquired cholesteatoma has an incidence of 1.2-7.1 per 1000 people. The mean age of affected individuals is 41.2 years.

• Metaplasia theory – Chronic inflammation results in a metaplastic transformation from the typical cuboidal epithelium of the middle ear into squamous epithelium.
• Basal hyperplasia theory – Chronic inflammation triggers active proliferation of the basal layer of the pars flaccida, forming microcysts that invaginate into the middle ear. These cysts later become filled with keratin and result in a cholesteatoma.
• Immigration theory – Cholesteatoma formation results from keratinizing squamous epithelium migrating from the outer surface of the tympanic membrane and external auditory canal into the middle ear via a perforation.
• Implantation theory – The implantation theory proposes the formation of cholesteatomas via accidental introduction of squamous epithelium into the tympanic membrane following surgery, trauma, or blast injury.
• Retraction pocket theory – This theory emphasizes eustachian tube dysfunction in the formation of cholesteatomas. The resulting negative pressure and lack of ventilation triggers a retraction pocket in the region of pars flaccida. Keratin fibers accumulate in the pocket and result in a cholesteatoma. Chronic infection and inflammation lead to a local inflammatory environment that fosters growth and migration of the lesion. Increased osteoclastic activity results in bone resorption of surrounding structures. Furthermore, bacteria such as Pseudomonas aeruginosa, Streptococcus, Staphylococcus, Proteus, Enterobacter, and anaerobes thrive in this environment. The retraction pocket theory is the most widely accepted.

Acquired cholesteatomas can be further divided into primary and secondary. Primary acquired lesions typically develop from a normal tympanic membrane. Conversely, secondary acquired lesions result from an abnormal tympanic membrane.

A large proportion of patients with cholesteatomas remain asymptomatic. Increased awareness and advancements in otoscopes have led to increased detection in the asymptomatic phase. As the lesion progresses and invades surrounding structures, compressive symptoms develop. Symptoms may include hearing loss, otalgia, aural fullness, pruritus, vertigo, tinnitus, and facial dysfunction. Cardinal symptoms include painless otorrhea and hearing loss and should prompt further workup.

Failure of expedient diagnosis and management can result in complications. Common complications include secondary infections, perilymph fistulas, destruction of ear ossicles, and cranial nerve palsies. If the lesion invades the temporal bone, subsequent abscess formation, mastoiditis, meningitis, and/or sigmoid sinus thrombosis can result. Evidence of intracranial involvement includes fever, seizures, headache, nausea, vomiting, and focal neurologic symptoms. It is imperative for clinicians to be aware of these signs as prompt antibiotic treatment is warranted.

Patients with a history of recurrent ear infections, external auditory canal stenosis, and postoperative or posttraumatic external auditory canal defects are at increased risk for cholesteatoma development.

Related topics: cholesteatoma, cholesteatoma of middle ear