CT FINDINGS:
Attic cholesteatoma,
the most common form of acquired cholesteatoma,
the pars flaccida,
posteriorly and superiorly located, invaginates toward the Prussak space.
Cholesteatoma has an erosive potential along the ossicles and bony walls of the middle ear cavity,
mostly by means of an inflammatory response that activates osteoclastic activity.
The main CT findings are the followings: (Fig 6,7,8).
- Soft tissue mass attenuation in Prussak space
- medial ossicular displacement by the growing cholesteatoma are specific findings at computed tomography (CT)
- Extension into the mastoid antrum
- 70% erosion of the ossicle
- Erosion of the scutum and the short process of incus.
- Tympanic membrane perforation
- Tympani tegmen defect
MRI FINDINGS:
With its high tissue discrimination and contrast resolution,
magnetic resonance imaging is valuable in diagnosis of cholesteatomas.
Let’s see the main techniques:
- Delayed postcontrast image (DPI): was the first specific MR imaging technique to be used in cholesteatoma diagnosis.
T1-weighted images are obtained 45–60 minutes after intravenous administration of paramagnetic contrast material.
Diagnosis is based on the lack of contrast enhancement in non perfused cholesteatomas as opposed to the enhancing granulation and inflammatory tissue.
- Diffusion-weighted imaging (DWI) is highly specific due to the high keratin content of cholesteatomas.The main diagnostic criterion for cholesteatoma at DWI is lesion hyperintensity,
compared with the signal intensity of brain,
on b = 0 sec/mm2 images that persists or increases on high b value (800–1000 sec/mm2) images.
(Fig 9)
- New non–echo-planar DWI sequences (Non-EPI DWI),
such as periodically rotated overlapping parallel lines (PROPELLER) with enhanced reconstruction,
are superior to conventional echo-planar DWI (EPI-DWI),
since they minimize susceptibility artifacts at the skull baseand increase sensitivity for detection of lesions as small as 2 mm.
This technique is indicated when clinical diagnosis is difficult and high tissue specificity is necessary,
as in congenital,
temporal bone,
or atypical acquired middle ear cholesteatomas and residual or recurrent disease after surgery.
Moreover,
Non–echo-planar DWI has been proposed for screening of postsurgical (residual or recurrent) cholesteatomas,
thus obviating many second-look revisionsurgeries,
especially after more conservative canal wall up surgery (Fig 10).
DIFFERENTIAL DIAGNOSIS:
Until the advent of DPI and DWI techniques,
specifically intended for cholesteatoma imaging results of MR imaging were nonspecific in demonstrating the different causes of middle ear inflammatory disease (mucosal edema,
granulation tissue,
fluid,
scar tissue,
or cholesteatoma) (Fig 12).
Except for the characteristic T1 hyperintensity of cholesterol granuloma,
all of these entities show variable degrees of T1 hypointensity and T2 hyperintensity,
mainly depending on their water and protein content.
- In congenital temporal or middle ear cholesteatomas,
the integrity of the tympanic membrane and their variable location,
together with their rarity and small size,
make clinical and otoscopic diagnosis difficult at times.
The high tissue specificity of DWI becomes useful in this clinical setting.
Given the small size of congenital cholesteatomas,
non-EPI sequences are preferred over less sensitive EPI DWI.
(Fig 13)
- Cholesterol granuloma of the middle ear,
unlike its counterpart in the petrous apex,
has little clinical relevance,
given its nonaggressive nature.
Coexistence with cholesteatoma is frequent due to their common etiologic factors (chronic middle ear disease,
hemorrhage,
surgery).
When differentiation from other causes of middle ear masses—such as fluid,
inflammatory mucosa,
granulation tissue,
cholesterol granuloma,
surgical scar,
or encephalocele isclinically relevant,
tissue-specific imaging techniques (MR imaging,
and more specifically diffusion-weighted imaging [DWI]) become very useful.
(Fig 14).
- Chronic otitis media shows retained inflammatory secretions,
which may also simulate a nonenhancing cholesteatoma.
For the ENT-surgeon the differentiation between chronic otitis media and cholesteatoma is important. Both diseases often occur in poorly pneumatized mastoids.
Erosion of the lateral wall of the epitympanum and of the ossicular chain is common in cholesteatoma (around 75%). Erosion can occur in chronic otitis,
but reportedly in less than 10% of patients.
Displacement of the ossicular chain can be seen in cholesteatoma,
not in chronic otitis. Cholesteatoma can present with a non-dependent mass while chronic otitis shows thickened mucosal lining. However,
in both diseases the middle ear cavity can be completely opacified,
obscuring a cholesteatoma (Fig 15).
INTRACRANEAL COMPLICATIONS:
- Encephalocele: Coronal high-resolution CT shows brain parenchyma filling the residual cavity (Fig 16*).
Findings related with temporal bone encephalocele as a complication of cholesteatoma.
Diagnosis of encephalocele is usually straightforward on coronal or sagittal T1- and T2-weighted high-resolution images.
- Labyrinthine fistula: The high resolution coronal CT shows an image of the right ear at the level of the horizontal semicircular canal. Note the complete erosion of the ossicle ,
the tegmen tympani and the fistula of the horizontal semicircular canal (Fig 17).
- Acute Labyrinthitis: Labyrinthitis has three radiologic stages: acute,
fibrous,
and labyrinthitis ossificans.In the acute stage,
contrast-enhanced T1-weighted MR imaging may show abnormal enhancement of the labyrinth.
MR imaging also allows detection of cochlear obstruction in the fibrous stage,
before abnormalities are detectable with CT .Labyrinthitis ossificans involves pathologic ossification of the bony labyrinth and cochlea and is well-depicted with CT (Fig 18).
- Facial Palsy: Perineural extension of a cholesteatoma along the facial nerve may also occur,
in which case MR imaging is important,
to exclude a neoplasm.
Sensorineural hearing loss develops by cholesteatomatous involvement of the internal auditory canal.
The labyrinthine segment of the facial nerve canal also appears widened.
The facial nerve enters the petrous bone via the internal auditory canal.
The nerve exits this canal anterioly along the facial canal.
The first genu of the facial nerve then passes around the anterior aspect of the otic vapsule of the inner ear (Fig 19).
POSTOPERATIVE CHOLESTEATOMA:
Identification of recurrent cholesteatoma and differentiation from postoperative granulation tissue is important in a patient who has undergone mastoidectomy for cholesteatoma.
The MR imaging findings of recurrent cholesteatoma include a hyperintense mass on T2-weighted images that has intermediate-to-low T1-weighted signal intensity and that enhances minimally after the administration of contrast material.
Cholesteatomas are hyperintense at DWI due to their high keratin content and show no enhancement at DPI(Fig 20).
In this slide we analyze the strengths and drawback of the very promising non-echo-planar imaging (non-EPI) versus EPI DWI tecniques.
(Fig 21).
Both EPI and non-EPI DWI techniques are highly specific for cholesteatoma.
Although false-positive results are described,
most of them are easily identifiable on the basis of the clinical context or type of surgery performed (Fig 22,23,24).
Until the advent of DPI and DWI techniques,
specifically intended for cholesteatoma imaging,
results of MR imaging were nonspecific in demonstrating the different causes of middle ear inflammatory disease (mucosal edema,
granulation tissue,
fluid,
scar tissue,
or cholesteatoma) but with the newest and very promising non-echo-planar imaging ( Non-EPI) DWI techniques that have been developed during the past decade the sensitivy and specificity for diagnosis of middle ear cholesteatoma have improved.