One of the main differentials for external auditory canal cholesteatoma (EACC) is keratosis obturans. What is the most important imaging finding in distinguishing both entities?
Both lesions may cause canal expansion. Erosion of the adjacent bony canal walls is an important feature of EACC, which is not seen in keratosis obturans.
List other important differential diagnoses for EACC.
Postinflammatory medial canal fibrosis, malignant (necrotizing) otitis externa and malignant masses of the external auditory canal (squamous cell carcinoma).
There is a rather large mass of soft tissue attenuation centered within the bony portion of the left external auditory canal, resulting in significant canal expansion and marked circumferential canal wall erosion with multiple small predominantly peripheral bony fragments.
Thinning and destructive changes of the tympanic and mastoid parts of the left temporal bone are noted, with a small amount of retained fluid within the left mastoid air cells.
The mass erodes the left scutum, extending into the left middle ear cleft, encasing and slightly eroding the left middle ear ossicular chain, obliterating the left Prussak space, aditus ad antrum and mastoid antrum.
Complete obliteration of the facial recess with thinning and erosion of the posterior genu and tympanic segment of the left facial nerve canal, suggestive of facial nerve involvement.