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. 

The vast majority of acquired cholesteatomas develop as a result of chronic middle ear infection and are usually associated with perforation of the tympanic membrane. Clinical presentation usually consists of conductive hearing loss, often with purulent discharge from the ear 6

Patients may also present due to one of many complications, which include: 

Cholesteatomas are composed of densely packed desquamated keratinizing squamous cells, arising from a peripheral shell of inward facing epithelium. As cells mature, they continue to be shed into the mass, resulting in slow growth 1-3

There are four hypotheses that relate to the formation of cholesteatomas; all may be true 1,6:

  • invagination / negative pressure
  • invasion/migration
    • in the setting of a previous perforation
    • keratinised cells 'invade' the middle ear through the perforation
  • basal cell hyperplasia and papillary ingrowth
    • invasive hyperplasia of the basal cell layer of the tympanic membrane as a result of infection
  • metaplasia
    • as a result of chronic irritation from middle ear infection
CT

CT is the modality of choice for diagnostic assessment of cholesteatomas, due to its ability to demonstrate the bony anatomy of the temporal bone in exquisite detail. Cholesteatomas appear as regions of soft tissue attenuation, exerting mass effect and resulting in bony erosion. 

Findings depend on the part of tympanic membrane the cholesteatoma arises from: 

  • pars flaccida (82%) 
    • superior extension: most common, it expands into Prussak's space, eventually eroding the scutum and displacing the ossicles medially
    • inferior extension: 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%)
MRI

Although MRI is unable to adequately delineate bony anatomy, it can potentially distinguish non-specific opacification from cholesteatomas. It is particularly useful in the postoperative setting when CT may be indeterminate, since granulation tissue, scarring and recurrent cholesteatoma may all appear similar 2

Cholesteatomas demonstrate:

  • T1: low signal
  • T2: high signal
  • T1 C+ (Gd): no enhancement
  • DWI: diffusion restriction

DWI is particularly useful when distinguishing a cholesteatoma from other middle ear masses. It is the only entity that demonstrates high signal intensity on DWI. However, the sequence is prone to artefact and care must be taken how the sequence is performed and interpreted 2

The mechanism responsible for a high signal on DWI remains somewhat uncertain but is thought to represent either T2 shine-through alone or in combination with true restricted diffusion 2-4.

Surgical excision is curative. However, recurrence is not uncommon because the lesion is often difficult to remove completely. 

The differential of a middle ear mass includes:

In the post-operative setting, the differential for a soft-tissue middle ear mass includes the entities above, but is usually restricted to three entities 2:

  • recurrent cholesteatoma
    • increased signal on DWI
    • no enhancement
    • high T1 signal
  • granulation tissue
    • intermediate T1 signal
    • enhancement
    • low signal on DWI
  • scarring
    • low T1 and T2 signal
    • low signal on DWI
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Article Information

rID: 841
System: Head & Neck
Section: Pathology
Synonyms or Alternate Spellings:
  • Acquired cholesteatomas
  • Acquired cholesteatomata

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