Acquired cholesteatoma

Acquired cholesteatomas make up 98% of all middle ear cholesteatomas, and are almost always closely related to the tympanic membrane, from which most are thought to arise.

Acquired cholesteatomas can also be divided into:

• Primary (no history of chronic otomastoiditis)
• Secondary

They can further be divided according to the part of the tympanic membrane from which they arise:

• pars flaccida (82%) - Extension superiorly is most common, where it expands into Prussak's space, eventually eroding the scutum and displacing the ossicles medially. Inferior extension is less common, but more frequently seen in children.
• pars tensa
  • posterosuperior (78%) - extends medial to the incus and displaces the ossicles laterally.
  • anterior and inferior (22%)

The pars flaccida cholesteatomas are more frequent in children and tend to be more aggressive.

There are four hypotheses as to how cholesteatomas are formed... all of which may be true in some cases:

1. Invagination - most common. Results from Eustachian tube dysfunction and tympanic membrane retraction, with debris and keratin eventually obstructing the neck of the retraction.
2. Invasion - common among perforations. Keratinized cells 'invade' the middle ear through the perforation.
3. Basal cell hyperplasia (unlikely)
4. Metaplasia (unlikely)

Complications=

• Labyrinthine fistula - episodic vertigo typical. Lateral semicircular canal is most frequently involved.
• Cochlear fistula - less common
• Perilymphatic fistula can be spontaneous or as a result of surgery to treat existing labarinthine or cochlear fistulas.
• Labyrinthitis
• Facial nerve dsyfunction including the rare inflammatory neuroma of the facial nerve.
• Extension through inner ear into internal acoustic meatus leading to deafness.
• Extension into the middle cranial fossa with possible meningitis, cerebral abscess etc...
• Extension into the petrous apex (rare) with similar complication as petrous apicitis.