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fluid or edematous mucosa on HRCT. In thisway, the selective use of HRCT and DW-MRI canprovide complementary information that canguide the otologic surgeon in the management of cholesteatoma.

HIGH-RESOLUTION COMPUTED

TOMOGRAPHYWith present CT scanner technology, a volumetricHRCT of temporal bone with 0.6 mm slice thickness

can be performed in about 40 s with minimal dis-comfort and no need for intravenous (i.v.) contrast.Reformatting can be performed at arbitrary planesfrom the original dataset in cases in which planarviews in nonstandard orientations may be helpful.

The strength of HRCT is its ability to imagebone. A cholesteatoma appears as abnormal appear-

ance of soft tissue, usually occurring in pneumatizedregions of the temporal bone. The normal aeration islost and the surrounding bone often shows evidenceof erosion with smooth or scalloped margins.Adjacent ossicles may be absent, eroded, or demin-eralized. The scutum is often eroded, revealingthe pathway of ingrowth of epithelium from thepars flaccida into the epitympanum(Fig. 1: coronal).

HRCT is also very useful in identifying thegeometry and location of adjacent vital structures.The inner ear, facial nerve, tegmen, sigmoid sinus,and carotid artery can all be seen quite readily onthe same sequence given their interface with bone.A careful study of the HRCT can reveal anatomicvariations that may impact surgery. Similarly, lossof the normal bone overlying any of these structuresmay give a valuable warning of involvement bycholesteatoma.

When ossicular or mastoid bony erosion isseen with a soft tissue density, HRCT can identifycholesteatoma with specificity between 80–90%[4,5] . However, HRCT has proven unreliable indifferentiating residual or recurrent cholesteatomafrom granulation tissue, cholesterol granuloma,mucosal edema, fibrosis, scar tissue, or fluid [6–8].In the postoperative period, HRCT has proven to bea method with high negative predictive valuewhen it shows a well aerated middle ear with no

KEY POINTS

HRCT scan provides a fast and reliable method forevaluating temporal bone anatomy and providesinvaluable information for primary cases of cholesteatoma. Useful in the postoperative period,with high negative predictive value when it shows adisease-free middle ear and mastoid.

DW-MRI has shown the highest sensitivity andspecificity in detecting recidivistic cholesteatoma.

Cholesteatomas of size 3 mm or larger can be detectedby DW-MRI and differentiated from granulation tissue,scar, and fibrosis.

Low-risk patients for developing residual or recurrentcholesteatomas can be stratified for serial DW-MRI andpotentially avoid additional surgery.

DW-MRI will likely decrease the quantities of second-look surgeries, decreasing patient morbidity andsurgical costs. Patients may still require second-looksurgery to address reconstruction of the conductivehearing mechanism of the middle ear.

(a) (b) (c)

FIGURE 1. Cone beam computed tomography scans of a patient with left cholesteatoma. Axial (a), coronal (b), and sagittal(c) orientations show diagnostic and therapeutic findings, including: a sclerotic mastoid with an erosive cholesteatoma (C),demonstrating scalloped edges, scutum erosion (S) and a demineralized ossicular chain (O). The subtle flattening over thelateral semicircular canal seen on the coronal image () is also indicative of progressive expansion. The tegmen (T) isdehiscent and low-lying, affording minimal surgical access to the epitympanum. There is tympanosclerosis medial to theossicular chain (TS). The facial nerve (FN), is shown to be dehiscent adjacent to the oval window on the coronal image, andthe chorda tympani can be seen on the sagittal reconstruction. A, anterior; C, Cholesteatoma; ChT, Chorda tympani; FN,facial nerve; L, left; O, ossicles; P, posterior; R, right; S, scutum; T, tegmen; TS, tympanosclerosis.

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of either single-shot turbo-spin sequences (HASTE:Half Fourier Acquisition Single Shot Turbo SpinEcho, (Siemens Systems, Germany) or multishotturbo-spin sequences [Periodically Rotated Over-lapping ParallEL Lines with Enhanced Recon-struction (PROPELLER); BLADE (Siemens Systems,Germany)].

One limitation of DWI is that it can yieldartifacts at the interface of varied anatomic tissues.These magnetic susceptibility artifacts correspondto the magnetization of adjacent tissues as a result of an external magnetic field. When two tissues withdifferent magnetic susceptibilities are juxtaposed,it causes local distortions in the magnetic field.Unfortunately, the mastoid and middle ear producesusceptibility artifacts due to natural air–bone inter-faces, which cause image distortion. This has beenshown in multiple studies, which have demon-strated its inability to detect cholesteatomas smallerthan 5 mm [6]. Studies have also shown newer,non-EPI DWI to be superior to EPI DWI i n d etectingrec urrent or residual cholesteatoma [22 && ,23,24,25 & ,26,30] , and thus non-EPI DWI has become thestandard for MRI imaging of cholesteatoma.Additionally, the patient cost generated in anMRI is approximately double that of an HRCT[32] . Although the clinician should consider thisadditional economic impact, the benefits gainedin selected patients by avoiding needless surgery,or by preventing a delay in diagnosis, can poten-tially justify its use on ec ono m ic groun ds.

Various recent studies [22 && ,23,24,25 & ,30] , inclu-ding a recent meta-analysis [28 & ], have evaluatedDW-MRI for the detection of residual and recurrentcholesteatomas. In the meta-analysis, the overallsensitivity for this imaging modality was 94% witha specificity of 94%. The majority of false-negativesreported were due to cholesteatoma pearls lessthan 3 mm in size. False-positives reported inthis study were due to susceptibility artifacts,cholesterol granuloma, abscess, or bone powder.

Indications for imaging

Experts may disagree about the indications of imaging and the extent to which it assists in treat-ment decisions [33] . Some otologists routinelyobtain imaging whenever cholesteatoma is eitherseen or suspected, whereas others use imaging onlywith great reservation. Most agree that imagingis indicated in revision cases and those with intra-cranial or intratemporal complications. Surgeonsshould carefully consider the benefits they receivefrom imaging in their particular practice, andregularly reevaluate these indications as they gainexperience and modify their surgical techniques.

Surgeons should always be diligent aboutreviewing imaging studies themselves, as eventhe best radiology report will rarely convey thesubtleties that affect surgery.

Preoperative assessmentThe benefits of knowing potential challenges,

and having a roadmap for surgical planning isparticularly helpful in teaching settings in whichexpectations for the case can be reviewed pre-operatively. Similarly, HRCT can be very helpfulprior to revision surgery, especially when thesurgeon did not perform the initial procedure.In revision cases, anatomy may be considerablyaltered, limiting the utility of normal surgicallandmarks and presenting unexpected challenges.

An HRCT study can reveal specific patterns of pneumatization and aeration or variability on theposition of the sigmoid sinus or tegmen, which mayaffect surgical access to disease. Is a mastoidectomyneeded, or can the disease be adequately accessedtranscanal? Is there likely to be adequate space toaccess disease while leaving the canal wall up, or isthe mastoid sclerotic and contracted, warranting aplanned canal-wall-down procedure? Erosion of theFallopian canal may be suggested, as could exposureof the carotid artery or jugular bulb, which couldserve as a warning to potential hazards duringdissection. Some semicircular canal dehiscencecan be clinically silent [34] , as are almost all facialnerve dehiscences, thus preoperative knowledgeof these findings may alert the surgeon to areas thatwarrant extra intraoperative attention. Althoughdifficult to assess completely, obvious ossicularabnormalities may predict the need for ossicularreconstruction. HRCT can also demonstrate un-expected and potentially unrelated anatomic vari-ation such as anomalous facial nerve patterns [35] .

Despite MRI’s superior ability to identify chole-steatoma and differentiate it from other soft tissues,it is seldom helpful in the preoperative setting inprimary cases. However, DW-MRI can provideadditional information in primary cases in whichclinical information is limited, or the otoscopic

examination is inconclusive (Fig. 2). The greatmajority of times, however, the diagnosis is notin doubt, and HRCT is superior in providinginformation on salient anatomic geometry. DW-MRI, however, becomes considerably more usefulin assessing the potential for postoperative recur-rence of disease. In such cases, cholesteatomamay appear in unexpected areas inaccessible toclinical otomicroscopy, including the mastoidcavity, deep to reconstructive materials, and grow-ing around adjacent structures in which the furthestextent of cholesteatoma may have been missed on





the primary procedure (Fig. 3). Conversely, not allhigh-signal intensites on DW-MRI are cholesteato-mas, as cholesterol granuloma may appear similar torecidivistic cholesteatoma (Fig. 4). In these cases, theuse of other MRI sequences may be very useful topredict the diagnosis, and provide the surgeon andpatient with expectations for treatment.

Postoperative surveillanceIt is compelling to look for alternatives to second-look surgery. If an HRCT shows no abnormalsoft tissue at 6 or 9 months following the initialstage, one may feel comfortable holding off on asecond look [4,6,9,33] . Unfortunately, it is rare thatan HRCT study will be entirely without somesuspicious soft tissue. Also, in an early postoperative

ear, one cannot use bone erosion to help differen-tiate the soft tissue from scar, fluid, or edema. This islikely the situation in which DW-MRI is most usefulin imaging cholesteatoma.

After 9–12 months, most persistent cholestea-tomas will be larger than 3 m m and ther efor e shouldbe apparent on DW-MRI [22 && ,23,24,25 & ,28 & ,29,30] .A negative DW-MRI study may avoid the expenseand morbidity associated with a negative secondlook. The surgeon needs to make the judgmentbased on the likely area of involvement on whethera recurrence of 3 mm or greater is unacceptablylarge. In some areas, such as at the mastoid cavity,a recurrent cyst of this size can usually be readilyresected. In other areas, such as the sinus tympanior on the stapes footplate, a cholesteatoma of

(a) (b)

FIGURE 2. (a) Axial high-resolution computed tomography (HRCT) scans of a patient with a primary left cholesteatoma,showing soft tissue on the epitympanum (). Although this finding is consistent with cholesteatoma, it is impossible todistinguish this from other soft tissues seen in chronic otitis media. (b) Diffusion-weighted (DW)-MRI of the same patient. Notethe bright area in the epitympanum () that corresponds to the soft tissue seen on the CT. The high signal results from restricteddiffusion of water within the keratin debris, and supports the diagnosis of cholesteatoma. This provides complementaryinformation to the anatomic detail seen on CT.

(a) (b)

FIGURE 3. Axial images of a recurrent cholesteatoma (arrows) eroding the mastoid tip air cells 25 years following a priorcanal-wall-up tympanomastoidectomy. The patient’s tympanic cavity showed no evidence of disease on otoscopy. (a) Diffusion-weighted (DW)-MRI shows a high signal lesion in the mastoid, consistent with cholesteatoma. (b) high-resolution computedtomography (HRCT) confirms an erosive soft tissue lesion with loss of bone over the sigmoid sinus (s) and posterior fossa dura.

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3 mm may present a prohibitively greater surgicalchallenge. If this is the case, foregoing imaging, andproceeding directly with a second-look procedureis very reasonable. If a DW-MRI study is negative at9–12 months postoperatively, the surgeon shoulduse his or her clinical judgment as to whetheranother scan is needed at a later date. In routinecases, in which recidivistic disease is likely to occurin the middle ear or mastoid, a single scan maywell be sufficient, and the patient can be followedclinically. If, however, there is concern for persist-ence in areas that are inherently more difficultto assess, such as the jugular foramen or petrousapex, another scan obtained a year later is a reason-able option.

Cholesteatoma complicationsIn patients with complications of chol est eatoma,imaging is almost always indicated [17 & ,18,30,36,37] . MRI is best suited for defining intracranialcomplications such as perimeningeal spread of infection, brain abscess, or sinus thrombosis.Intratemporal complications with facial paralysis,extension into the labyrinth, petrous apex or jugularforamen are best identified by HRCT. However inthe majority of complications, the clinician maywish to obtain both HRCT and MRI studies, as bothmay offer valuable insights with diagnostic andtherapeutic implications.

CONCLUSION

HRCT scan and DW-MRI have proven to becomplementary scanning modalities and reliablemethods for detecting and characterizing chole-steatoma. HRCT still provides a useful roadmap

for surgery which can help guide the surgeon tomore safe and effective management. Current liter-ature suggests DW-MRI to have a high sensitivityand specificity in detecting cholesteatoma downto 3 mm in size. It also provides adequate differen-tiation between cholesteatoma and other soft tissuedensities including granulation tissue, fibrosis,mucosal edema or scar. As more centers implementDW-MRI for detecting residual or recurrent chole-steatoma, the need for second-look surgery to evalu-ate for the presence of residual or recurrent diseasewill likely reduce and even replace surgery, therebydecreasing patient morbidity and surgical costs.

AcknowledgementsNone.

Conflicts of interestThe authors have no relevant financial disclosures or conflict of interest.No funding to disclose.

REFERENCES AND RECOMMENDED

READINGPapers of particular interest, published within the annual period of review, havebeen highlighted as:& of special interest&& of outstanding interestAdditional references related to this topic can also be found in the CurrentWorld Literature section in this issue (p. 510).

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(b)(a)

FIGURE 4. Axial images of a cholesterol granuloma presenting as an expansile mastoid lesion (arrows) 6 years followingtympanomastoid surgery for cholesteatoma. (a) Diffusion-weighted (DW)-MRI showing heterogeneous high signal on aPROPELLER DWI sequence. It is important to note that such restricted diffusion can occur in disease other than cholesteatomas demonstrated here. By correlating this with the image shown in (b), the lesion is seen to have inherently high signal onT1-weighted sequences (unlike the low signal expected for cholesteatoma), suggesting the diagnosis of cholesterol granuloma.





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