High resolution computed tomography of the temporal bone has an excellent spatial resolution, thus even small soft-tissue lesions of the temporal bone can be accurately delineated. However, CT has poor specificity. CT is required preoperative to exclude perforation of the bone.  [1,2] [Fig.1]

Although MRI is unable to adequately delineate bony anatomy, it can potentially distinguish non-specific opacification from cholesteatomas. It can be used to detect them when the physical examination is difficult and CT findings are ambivalent.

Non-contrast MR imaging with diffusion-weighted imaging is recommended in all patients with a suspicion of cholesteatoma. It is particularly useful in the postoperative setting when CT may be indeterminate, since granulation tissue, scarring and recurrent cholesteatoma may all appear similar. 

If negative, it can avoid "second look" surgery. 

MRI is particularly useful for evaluating the extension of a cholesteatoma into the middle and posterior fossa, and for demonstrating possible herniation of intracranial contents into the temporal bone - especially after surgery. [fig2,3]

Newer techniques allow detection of small lesions and may be sufficient to replace second-look surgery in patients with prior cholesteatoma resection.  [4]

Cholesteatomas demonstrate:

Diffusion weighted imaging is particularly useful when distinguishing a cholesteatoma from other middle ear masses. This techniques, are capable of differentiating cholesteatoma from inflammatory tissue cholesterol granuloma and granulation tissues. Diffusion weighted MR can differentiate between a cholesteatoma, which has a restricted diffusion, and other pathologies - especially granulation tissue - which have normal diffusion characteristics. It is the only entity that demonstrates high signal intensity on DWI. [7,8,9] fig [4]