EDUCATIONAL REVIEW Open Access

HRCT imaging of acquired cholesteatoma: apictorial reviewMalvika Gulati, Swati Gupta* , Anjali Prakash, Anju Garg and Rashmi Dixit

Abstract

Chronically discharging ear is a common cause of morbidity in developing countries, and it is also associated withintratemporal and intracranial complications. The surgeon is often able to detect the disease. However,cholesteatoma in the “hidden areas” like anterior epitympanic recess and sinus tympani can be missed. Facial nerveinvolvement and cholesteatomatous erosion of the bony labyrinth are dreaded complications, the extent of whichcannot be assessed completely on clinical examination. Adding to the complexity are the various variations inanatomy like high riding jugular bulb and aberrant internal carotid artery which could lead to catastrophiccomplications during surgery if left undetected preoperatively. HRCT temporal bone is useful to detect the extentof the disease, various complications, and guide the surgeon for pre-operative planning. In this review, we gothrough the various HRCT imaging features of acquired cholesteatoma, a reporting template, and a few wordsabout imaging of the post-operative ear.

Keywords: Cholesteatoma, Complication, High-resolution computed tomography, Mastoidectomy, Facial nerve

Key points

� Acquired cholesteatoma is commonly associatedwith intratemporal and intracranial complications.

� Various “hidden areas” in the middle ear that arenot amenable to clinical examination can be easilyseen with HRCT.

� The extent of disease and complications can beassessed.

� Variant anatomy can be looked for to avoid intra-operative complications.

IntroductionCholesteatoma is a condition prevalent around theworld, predominantly in developing countries. Acquiredcholesteatoma is a common complication of unsafe/atti-coantral chronic otitis media. Literally, it means thepresence of “skin in the wrong place.” The cholesteato-matous sac is lined by stratified squamous epitheliumconstituting the matrix, which secretes the acellularkeratin debris within [1]. An outer perimatrix contains

mesenchymal cells which produce proteolytic bonedestroying enzymes [2, 3].Cholesteatoma can be classified as congenital or ac-

quired. Another system of categorization could be ac-cording to the location of the cholesteatoma, whichcould be in the external auditory canal or middle earcavity and other pneumatised parts of the temporalbone. HRCT temporal bone is currently advocated in allcases suspected of cholesteatoma clinically prior to sur-gery for assessment of the extent of disease, complica-tions, and presence of variant anatomy.

Theories regarding the formation of acquiredcholesteatomaVarious theories exist regarding the formation ofcholesteatoma; however, none of them explain itcompletely.

Retraction pocket (invagination) theoryBeing the most widely accepted theory, it states that theweakest part of the tympanic membrane (TM), i.e., parsflaccida, retracts because of the negative pressure in themiddle ear cavity caused by long-standing eustachiantube dysfunction. This leads to the formation of postero-superior attic pockets. The self-cleansing mechanism of

© The Author(s). 2019 Open Access This article is distributed under the terms of the Creative Commons Attribution 4.0International License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, andreproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link tothe Creative Commons license, and indicate if changes were made.

* Correspondence: me.drswati@gmail.comDepartment of Radiodiagnosis, Maulana Azad Medical College, Bahadur ShahZafar Marg, New Delhi 110002, India

Insights into ImagingGulati et al. Insights into Imaging (2019) 10:92 https://doi.org/10.1186/s13244-019-0782-y

these pockets is gradually lost with the accumulation ofdesquamation keratinized epithelial layer of the TM andresults in the formation of keratin debris. Repeatedsuperadded infection occurs and later biofilms are alsoformed over these debris which make them resistant toany antimicrobial therapy [4].

InvasionIt is also hypothesized that there is an invasion of thekeratinized squamous epithelium into the middle earcavity through small perforations in pars tensa, whichforms cholesteatoma.

MetaplasiaDue to the chronic irritation, the keratinized squamousepithelium is formed from the squamous or cuboidalepithelium of the middle ear.

Basal cell hyperplasiaThere is a presence of microscopic defects even in theintact TM, through which epithelial cells can invade.These defects serve as direct contact between connectivetissue of the mucoperiosteum with a middle ear effusion.In later stages, these areas become totally or partially

covered with epithelium, and these epithelial breaks be-come connected to each other through the organized ef-fusion. The cholesteatoma seems to spread by using theconnective tissue as scaffolding [5].Thus, acquired cholesteatomas can be classified based

on the underlying pathogenesis as either “primary” or“secondary” where primary variety is seen behind parsflaccida of an intact retracted TM and the secondaryvariety grows into the middle ear through a perforatedpars tensa part of TM [1].The etiology of bony destruction by cholesteatomas is

also debatable. Destruction only by mechanical pressureis unlikely. One of the theories states that production ofdegrading enzymes by osteoclasts is the cause of bonydestruction [6, 7]. Due to its propensity to erode bone,the cholesteatoma can give rise to serious intracranialand extracranial complications.

Clinical featuresClinically, the lesion presents with foul-smelling otor-rhea, earache, and hearing loss. On otoscopic examin-ation, it classically appears as a cluster of pearly whitestructures in the attic region. It is also suspected beneathpolyps protruding from the pars flaccida or when thereis a marginal TM perforation or granulation tissue [8].Erosion of facial nerve canal can lead to features of

lower motor neuron palsy manifesting as an inability toclose ipsilateral eye, drooping of the corner of themouth, and drooling of saliva. A large proportion of pa-tients with facial canal erosion may not have features offacial nerve paresis. A labyrinthine fistula will lead tovertigo and nystagmus; however, these symptoms maybe present in the absence of a fistula, often due to thediffusion of toxic substances into the intact labyrinthine.Intracranial complications can be life-threatening, pa-tients presenting with fever, headache, and nuchal rigid-ity due to meningitis. The most common etiology of thecerebellar abscess is otogenic and patients present withfever and ataxia and other balance abnormalities.

Technique of HRCT studyNon-contrast axial scans parallel to the axis of andthrough the petrous temporal bone are acquired on a mul-tidetector CT scanner. Axial scanning is done with helical

Fig. 1 Axial CT image showing non-dependent soft tissue in thePrussack’s space, lateral to ossicles in a patient with pars flaccidacholesteatoma (arrow)

Fig. 2 Coronal CT image showing normal scutum on the left side (arrow). It is seen as a point of superior attachment of the tympanicmembrane. Scutum is eroded on the right side with soft tissue seen in the middle ear and external auditory canal

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technique (120 kVp, high-resolution matrix (512 × 512),section thickness 0.6–1mm, FOV 15–20 cm) in bone al-gorithm. Head is kept in neutral position and true axialimages parallel to Reid’s line (joining inferior margin ofthe orbit to the center of the orifice of EAC) are acquired.Coronal multiplanar reconstruction is made perpendicularto the axial scans.

Types of cholesteatomaCholesteatoma can be congenital or acquired. Congenitalcholesteatoma of the temporal bone is formed due tolack of involution of distinct squamous cell rest, whichshould have involuted to become normal endothelium

[1]. Middle ear cavity including mastoid, petrous, andsquamous portion of the temporal bone and TM are fre-quent sites of congenital cholesteatoma. Another loca-tion is intradural (cisternal) usually involving thecerebellopontine angle (CPA) and the patient presentswith varying degrees of hearing loss [9, 10]. A solitarylytic calvarial lesion may be cholesteatoma in the diploicspace. They are usually incidental findings on imagingand history of ear discharge or previous otologic proced-ure is lacking. Usually, the TM is intact and retractionpockets are not seen in such cases. Presence of

Fig. 3 Axial CT reveals widening of aditus (denoted by A) andformation of common cavity between epitympanum (denoted by E)and aditus with soft tissue within

Fig. 4 Axial CT image showing non-dependent soft tissue medial toossicles in a patient with pars tensa cholesteatoma (arrow)

Fig. 5 Axial CT through the mesotympanum shows the sinustympani (yellow arrow) and facial recess (white arrow) which arehidden areas by otological examination and should be carefullyinspected on imaging for the presence of soft tissue.

Fig. 6 Axial section through the epitympanum shows the normalanterior epitympanic recess (arrow) which is the medial extension ofepitympanum. Its importance lies in its close proximity to thetympanic segment of the facial nerve canal (*)

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cholesteatoma in the anterosuperior part of the middleear cavity just above the opening of the eustachian tubeshould raise the suspicion of congenital etiology [2].The other type of cholesteatoma is the acquired variety.

The acquired variety can be further classified according tothe location of the cholesteatoma in the external or themiddle ear.EAC cholesteatoma is uncommon and usually occurs

in an age group older than middle ear cholesteatoma. Itappears as a soft tissue mass in the canal particularlyalong its floor with associated bony destruction and peri-ostitis. It occurs due to the invasion of the squamousepithelium lining the EAC into the underlying bone.However, it is difficult to distinguish between

cholesteatoma, carcinoma, and malignant otitis externausing HRCT alone [2, 11].Among the middle ear cholesteatoma, the most common

type is pars flaccida variety and is seen characteristically inthe Prussack’s space, a niche in the epitympanum lateral tothe ossicles. These cause medial displacement of themalleus and erosion of the bony scutum, extending into theaditus and antrum posteriorly (Figs. 1 and 2). Widening ofthe aditus and formation of a common cavity are a charac-teristic feature [12, 13] (Fig. 3).Pars tensa variety is less common and usually arise

within retraction pockets. Pars tensa cholesteatoma dis-places the ossicles laterally in contrast to pars flaccidavariety [9] (Fig. 4). Careful inspection of sinus tympaniand facial recess is necessary as these areas are not vis-ible on otoscopic examination (Fig. 5). Another import-ant location in the middle ear is anterior epitympanicrecess also called supratubal recess, which is the medialmost extension of the epitympanum. A bony bar calledcog which is attached to the tegmen anterior to themalleus forms the boundary between anterior epitympa-nic recess and epitympanic cavity. Medially, this recessis in close relation to the proximal part of tympanic seg-ment of the facial nerve and geniculate ganglion, and de-hiscence of the bony partition can make the facial nerveprone to injury [14, 15] (Fig. 6)

Imaging features of cholesteatomaThe hallmark of cholesteatoma is bony destruction. Pres-ence of soft tissue density in the middle ear cavity coexist-ent with ossicular and mastoid bony erosion is highlyspecific for cholesteatoma. In attic cholesteatomas, the in-growth of epithelium from the pars flaccida into the epi-tympanum is evident by the erosion of the scutum.Ossicular erosion is more frequently encountered in

pars tensa cholesteatoma than pars flaccida location ofsoft tissue. Ossicles may not be visualized, appear rarefied,or show small erosions. Lenticular process of the incus ismost prone to erosion, due to poor ligamentous supportand precarious arterial supply by end arteries. Disruptionof the “ice cream cone” configuration of ossicles in epi-tympanum is seen frequently in attic cholesteatoma wherethe “ice cream scoop” is the head of the malleus and thebody of the incus represents “the cone” (Figs. 7 and 8).Careful inspection of the footplate of stapes at oval win-dow niche is also particularly important. Although the de-gree of ossicular erosion does not alter the need forsurgery, it can help prognosticate the patient regarding re-covery of hearing loss after surgery and aids in planningthe reconstructive procedure. For instance, patients show-ing erosion of stapes superstructure experience a muchhigher degree of hearing loss compared to patients withintactness of the same. Correlation for ossicular erosion

Fig. 7 Axial CT shows normal “ice cream cone” configuration ofossicles in epitympanum on the left side formed by the head of themalleus and the body of the incus. The right ear shows soft tissue inthe middle ear and aditus with non-visualization of ice cream conesuggesting erosion. A large defect is also seen in the sinodural plateon the right side (yellow arrow). Left sinodural plate is intact(white arrow)

Fig. 8 Axial CT shows soft tissue in the mesotympanum (M) witherosion of long process of incus and stapes which are not visualizedin their expected locations. The line diagram illustrates the normallocation of stapes (red) and long process of incus (yellow).

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between CT and surgical findings is higher for themalleus, body, and short process of incus when comparedto the long process of incus and stapes.However, in the absence of bony erosions, diagnosis of

cholesteatomas is challenging on CT. Presence of non-de-pendant soft tissue goes in favor of cholesteatoma. Also,mass effect on the ossicles is frequently seen in cholestea-tomas, even in the absence of frank destruction [2].Erosion of the facial nerve canal is an important com-

plication. Tympanic/horizontal segment is the mostfrequently affected. A limitation exists in evaluatingthe facial canal as it can be so thin even in the non-pathological ear that it becomes difficult to assess thepresence of its erosion in the affected ear. This ex-plains for the poor radiological correlation with thesurgical findings [16, 17]. In addition, visualizing thetympanic portion of the facial canal is found to be es-pecially difficult when there is an adjacent pathologicsoft tissue in the mesotympanum [8]. Routinely, axialand coronal reconstructions are seen to evaluate thefacial canal (Fig. 9a, b). Double oblique sagittal

images, along the plane of tympanic segment, aid inbetter visualization of this segment (Fig. 10).Labyrinthine fistula is a dreaded complication of cho-

lesteatoma. The most commonly affected is the lateralsemi-circular canal due to its close proximity to the mid-dle ear cavity (Fig. 11). Extensive disease can affect coch-lea and other semi-circular canals also. Fistula formationis seen as direct contact between the soft tissue andmembranous labyrinth. Hence, detailed inspection of thelabyrinth is necessary in axial and coronal planes. Eventhen, very small fistulae can be missed. The presence ofcholesteatoma in close proximity to the bony labyrinthalso needs to be reported even in the presence of intactintervening bone, due to the danger to the underlyinglabyrinth during surgery [18].Erosion of lateral mastoid cortex is also commonly

seen (Fig. 9b).Extensive bony destruction of the mastoid and ossicles

can occur which may give the appearance similar topostsurgical cases termed as automastoidectomy. Spon-taneous evacuation of cholesteatoma may be seen with

Fig. 9 Coronal (a) CT image reveals the “snail eye” view where the turns of cochlea form the body of snail and labyrinthine and tympanicsegments of facial nerve being the eyes (arrow). Coronal (b) CT image shows the erosion of the floor of the horizontal segment of the facialcanal (arrow). Erosion of lateral mastoid cortex is also seen (asterisk)

Fig. 10 Axial (a) and coronal (b) reference CT images show plane of reconstruction (blue line) to form the double oblique sagittal (c) imageshowing normal anatomy of tympanic (yellow arrow) and mastoid segments (white arrow) of the facial nerve canal

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this, termed as mural cholesteatoma leaving behind noresidual mass [2] (Fig. 12).Other sites of erosion include tegmen tympani (Fig. 13)

and sinodural plate (Fig. 7). Erosion of the sinodural plateis known to be a common implicating cause of transversesinus thrombosis, meningitis, cerebritis, and abscess. Insuspected intracranial complications, MRI is the investiga-tion of choice.

Differential diagnosisThe differential diagnosis of soft tissue in the middle earwith bony erosions includes cholesteatoma, facial nerveschwannoma/hemangioma, paraganglioma, rhabdomyo-sarcoma, LCH (Langerhans cell histiocytosis), squamouscell carcinoma, metastasis, and GCT (giant cell tumor)[1]. The presence of retraction of tympanic membranepoints towards chronic suppurative otitis media as theetiology [18].HRCT is unreliable in differentiating residual or recur-

rent cholesteatoma from other entities which usuallyoccur without bone destruction, like granulation tissue,cholesterol granuloma, post-inflammatory ossicular fix-ation, mucosal edema, fibrosis, scar tissue, and fluid.

They are also frequently encountered in the post-opera-tive period. MR imaging can usually aid in making thecorrect diagnosis as cholesteatomas are hypointense onT1WI, hyperintense on T2WI, do not show any en-hancement, and demonstrate diffusion restriction onDWI. Cholesterol granulomas on the other hand showhyperintense signal on T1WI due to the presence of in-trinsic blood products [2]. Post-inflammatory ossicularfixation is a complication of non-cholesteatomatouschronic otitis media and appears as soft tissue densityencasing the ossicles particularly in the oval windowniche with or without calcific foci. Absence of ear dis-charge and the presence of calcification or fibro-osseoustissue are pointers towards non-cholesteatomatous eti-ology [18].

Preoperative assessmentIn addition to the evaluation of complications of choles-teatoma, imaging also helps in warning the surgeon ofany variant anatomy that may predispose to life-threat-ening consequences during surgery or may affect surgi-cal access to disease such as the following:

� Dehiscent facial canal� High and dehiscent jugular bulb� Anteriorly lying sigmoid sinus� Low lying tegmen and dura [8]� Specific patterns of pneumatization and aeration of

mastoid [19].

Imaging of post-operative earImaging is of particular importance in patients who haveundergone canal wall up procedures where rates of re-currence range from 18–36%, and detection of residualor recurrent disease by otoscopic means is particularlytough [20].In the postoperative period, HRCT has a high negative

predictive value in cases with no evidence of soft tissuedensities. However, bony erosion in patients who havepreviously undergone a tympanomastoidectomy cannotbe characterized, as it is impossible to differentiate be-tween surgical changes and pathological bony destruction

Fig. 11 Axial CT image showing erosion of the lateral wall of thelateral semicircular canal (arrow) with the formation oflabyrinthine fistula

Fig. 12 Axial CT shows the right mastoid cavity filled with soft tissue and is seen to open directly into the external auditory canal suggestingautomastoidectomy (arrow)

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due to cholesteatoma. In this setting, HRCT has a sensitiv-ity of 43%, specificity of 42–51%, and a predictive value of28% for detection of residual or recurrent cholesteatoma.HRCT also plays a major role prior to revision surgery, asanatomy may be considerably altered, limiting the utilityof normal surgical landmarks [19].If an HRCT shows no abnormal soft tissue at 6 or 9

months following the initial surgical procedure, the sur-geon may be more confident in delaying a second-looksurgery [19].

Limitations of HRCTHRCT temporal bone has certain limitations. It is difficultto differentiate cholesteatoma from granulation tissue, pus,or fluid. Early disease with the absence of osseous erosion ischallenging to pick. The integrity of the facial canal cannotbe accurately commented upon, especially in the presenceof adjacent soft tissue in the middle ear. Due to the acquisi-tion of the non-contrast scan, intracranial complications arefrequently overlooked.

Checklist for acquired cholesteatoma on CT

� Location of mass—epitympanum/mesotympanum/hypotympanum

� Hidden areas—sinus tympani, facial recess, anteriorepitympanum recess

� Ossicles� Osseous walls of the middle ear� Mastoid air cells, aditus� Tegmen tympani, sinodural plate, scutum� Facial canal� External auditory canal and tympanic membrane� Inner ear esp. lateral semi-circular canal� Petrous apex, intracranial abnormality, post-

auricular soft tissue� Variant anatomy

ConclusionsHRCT temporal bone offers an insight into the extent ofcholesteatoma and the various complications before thesurgeon embarks onto the definitive line of management.It also helps detects recurrent/residual middle ear dis-ease to avoid unnecessary second-look surgery.

AbbreviationsCPA: Cerebellopontine angle; DWI: Diffusion-weighted imaging; EAC: Externalauditory canal; esp.: Especially; FOV: Field of view; GCT: Giant cell tumor;HRCT: High-resolution computed tomography; KVp: Kilovolt peak;LCH: Langerhans cell histiocytosis; MR: Magnetic resonance; TM: Tympanicmembrane; WI: Weighted images

AcknowledgementsNot applicable.

Authors’ contributionsMG and SG are the guarantors of integrity of the entire study andcontributed to the study concepts and design, literature research,manuscript preparation, and manuscript editing. AP, AG, and RD contributedto the study concepts and design and manuscript editing. All authors readand approved the final manuscript.

FundingNo funding received

Availability of data and materialsNot applicable

Ethics approval and consent to participateNot applicable.

Consent for publicationNot applicable.

Competing interestsThe authors declare that they have no competing interests

Received: 26 June 2019 Accepted: 15 August 2019

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