Opacification of the middle ear and mastoid: imaging findings and clues to differential diagnosis

Clinical Radiology xxx (2014) e1ee13

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Opacification of the middle ear and mastoid: imaging findings and clues to differential diagnosis A.C.C. Lo a, b, S.F. Nemec b, * a

Department of Radiology, Middlemore Hospital Auckland, Hospital Road, Otahuhu, Auckland 1640, New Zealand b Department of Biomedical Imaging and Image-guided Therapy, Medical University of Vienna, Waehringer Guertel 18-20, A-1090 Vienna, Austria

art icl e i nformat ion Article history: Received 23 September 2014 Received in revised form 19 November 2014 Accepted 26 November 2014

Opacification of the middle ear and mastoid represents a spectrum of inflammatory, neoplastic, vascular, fibro-osseous, and traumatic changes. This article reviews the most important clinical and pathological characteristics, emphasizing CT and MRI findings. Knowledge of subtle patterns of middle ear and mastoid opacification at CT and MRI provide guidance towards the correct diagnosis. Ó 2014 The Royal College of Radiologists. Published by Elsevier Ltd. All rights reserved.

Introduction Causes of middle ear and mastoid opacification encompass a clinically, radiologically, and histopathologically heterogeneous group of inflammatory, neoplastic, vascular, fibro-osseous, and traumatic changes.1,2 Changes can be local, however more diffuse involvement may affect even the inner ear or exhibit intracranial extension.1,2 The diagnostic impact can be significant, given the potential for hearing loss, pain, tinnitus, vertigo, and cranial nerve neuropathies. Assessment alongside otoscopic findings through the tympanic membrane is vital, providing potential clues towards the aetiology. For example, a “blue” hue in a cholesterol granuloma or a dehiscent jugular bulb, a “white” lesion in cholesteatoma or schwannoma, or a “red” lesion in a glomus tumour or an aberrant internal carotid artery (ICA) may be visualized.1

For assessment, CT is the primary imaging agent due to excellent spatial resolution and thin section thickness (
1 mm) enabling detailed evaluation of temporal bone opacification and the ossicles.1e5 MRI provides added softtissue lesion characterization and excellent evaluation of inner ear and cranial nerve involvement.2e4,6 This article details the different causes of middle ear and mastoid opacification, with a focus on CT and MRI, providing a pragmatic framework for the formulation of possible differential and top diagnoses. In this article, the term “opacification” will also refer to abnormal MRI signal intensities. Tables 1e4 summarize major clinical and radiological findings.

Infectious and non-infectious inflammatory diseases (Table 1) Acute otomastoiditis (AOM)

* Guarantor and correspondent: S. F. Nemec, Department of Biomedical Imaging and Image-guided Therapy, Medical University of Vienna, Waehringer Guertel 18-20, A-1090 Vienna, Austria. Tel.: þ43 1404004818; fax: þ43 1404004898. E-mail address: [email protected] (S.F. Nemec).

AOM is the most common temporal bone inflammatory condition, characterized by bacterial spread from the nose and nasopharynx to the temporal bone, usually after

http://dx.doi.org/10.1016/j.crad.2014.11.014 0009-9260/Ó 2014 The Royal College of Radiologists. Published by Elsevier Ltd. All rights reserved.

Please cite this article in press as: Lo ACC, Nemec SF, Opacification of the middle ear and mastoid: imaging findings and clues to differential diagnosis, Clinical Radiology (2014), http://dx.doi.org/10.1016/j.crad.2014.11.014

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Table 1 Middle ear and mastoid infectious/inflammatory diseases: summary of clinical and radiologic findings. Disease

Key clinical features

Key CT findings

Key MRI findings

Acute otomastoiditis

Common in children. Fevers, otalgia, otorrhoea, retro-auricular swelling

Middle ear and mastoid opacification with fluid levels, possible bone destruction

Necrotizing otitis externa

Elderly, diabetic, or immunocompromised patients. Fevers, otorrhoea, severe unremitting otalgia, usually Pseudomonas infection Conductive hearing loss, otorrhoea, tympanic membrane thickening  retraction

Extensive soft-tissue inflammation with middle ear and mastoid opacification. Skull base osteomyelitis causing bony destruction Middle ear and mastoid opacification with mastoid trabeculae thickening, sclerosis, and cell obliteration. Possible ossicular chain erosion Tympanic calcifications mimicking “extra ossicles”, “too well seen” stapes, tympanic membrane calcification Unenhancing tympanic  mastoid softtissue lesion. Possible smooth wall scalloping, ossicular displacement, or erosion Middle ear and/or mastoid soft-tissue opacification with ossicular, tegmen tympani, or scutum erosions. Possible labyrinthine fistulas

High T2W signal inflammatory material. Complications such as labyrinthitis, dural venous thrombosis, abscess formation, meningitis, petrous apicitis High T2W signal soft-tissue inflammation. Low T1W, high T2W/STIR signal in skull base osteomyelitis. Possible inflammatory cranial nerve enhancement High T2W signal inflammatory material, contrast-enhancing granulation tissue

Chronic otomastoiditis

Tympanosclerosis

Cholesterol granuloma

Cholesteatoma

Background of chronic otitis. Asymptomatic or conductive hearing loss Background of chronic otitis. Conductive hearing loss, “blue” tympanic membrane Congenital or acquired. Hearing loss, otorrhoea, white “pearly” lesion on otoscopy

No typical findings. Possible high T2W signal inflammatory material due to background chronic otitis Unenhancing lesion with high T1W, high T2W signal. No diffusion restriction

Lesion with low T1W and intermediate to high T2W signal and restricted diffusion, possible rim enhancement

Table 2 Neoplastic diseases: summary of clinical and radiologic findings. Disease

Key clinical features

Key CT findings

Key MRI findings

Glomus tympanicum tumour Glomus jugulotympanicum tumour

Pulsatile tinnitus, hearing loss, vertigo. “Red” middle ear lesion on otoscopy Pulsatile tinnitus, hearing loss, vertigo. “Red” middle ear lesion on otoscopy

Focal low T1W, high T2W signal, avidly contrast-enhancing lesion Low T1W, high T2W signal lesion with possible “salt and pepper” appearance, avid contrast-enhancement

Facial schwannoma

Varying facial paresis, hemifacial spasm, tinnitus, conductive hearing loss

Small contrast-enhancing focal mass at cochlear promontory Poorly defined avidly contrast-enhancing soft-tissue mass between middle ear and jugular fossa. “Permeativeedestructive” or “moth-eaten” bone destruction Contrast-enhancing lesion with smooth “benign” expansion of facial nerve canal

Middle ear adenoma

Adults. Conductive hearing loss, aural fullness, tinnitus, rare facial nerve dysfunction

Small focal tympanic soft-tissue lesion, typically no bone invasion

mucosal disruption from a viral upper respiratory infection.2 Young children are particularly affected due to hypertrophied adenoidal tissue and the relatively horizontal Eustachian tube, producing obstruction with subsequent air resorption and fluid extravasation into the middle ear and mastoid.2,5 Patients can present with fevers, otalgia, otorrhoea, or retro-auricular swelling.7 Although most patients

Low T1W, high T2W signal contrast-enhancing lesion. Focal lesion or multiple nerve segment involvement Low T1W, high T2W lesion with contrast-enhancement

with AOM undergo no imaging, it is necessary in suspected complications such as coalescent AOM.2,3,5 Histology shows pus and granulation tissue, and cultures may grow Streptococcus pneumoniae or Haemophilus influenzae.7 At CT, there is opacification of the tympanic cavity and/or mastoid, with possible fluid levels. In complicated cases, coalescent AOM may develop, characterized by

Table 3 Vascular conditions: summary of clinical and radiologic findings. Disease

Key clinical features

Key CT findings

Key MRI Findings

Facial nerve venous malformation Aberrant carotid artery

Atypical Bell’s palsy

Poorly defined lesion along facial nerve course with “honeycomb” osseous matrix Contrast-enhancing tympanic tubular structure in continuity with distal ICA through dehiscent carotid plate. Lateralized ICA course

Mixed T1W, high T2W signal lesion along facial nerve showing avid contrast enhancement

Asymptomatic, pulsatile tinnitus, conductive hearing loss. Vascular “red” lesion on otoscopy

Tubular structure in continuity with distal ICA. Lateralized course of aberrant ICA

ICA, internal carotid artery.

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Table 4 Fibro-osseous and traumatic conditions: summary of clinical and radiologic findings. Disease

Key clinical features

Key CT findings

Key MRI findings

Fibrous Children, young adults. Sporadic or in Well-circumscribed expansile “ground-glass” dysplasia McCuneeAlbright syndrome. Focal deformity, lesion conforming to bone configuration. conductive hearing loss, or recurrent otitis EAC stenosis, tympanic, and mastoid cell obliteration. Usually spares otic capsule Temporal High-energy force. EAC blood products, High-density opacification and fluid levels bone haemotympanum, pain, vertigo, hearing of tympanic cavity and mastoid, fractures, trauma loss, facial nerve dysfunction, cerebrospinal ossicular chain dislocation, pneumolabyrinth, fluid leak perilymphatic fistula

Mimics tumour: expansile lesion with low T1W, varied T2W signal, varied contrast-enhancement High T1W and T2W haemorrhagic signal. Loss of expected labyrinthine signal or presence of contrast-enhancement from otic capsule damage. Possible facial nerve injury with contrast-enhancement

EAC, external auditory canal.

mastoid trabeculae and cortical destruction (Fig 1a). A possible resulting subperiosteal abscess may lead to a rare Bezold abscess, where infection extends between the digastric and sternocleidomastoid muscles.2,8,9 At MRI, AOM presents as tympanic and mastoid high T2-weighted (W) signal material. Contrast-enhanced MRI (CE-MRI) is useful in assessing complications, such as labyrinthitis seen as inner ear contrast-enhancement, dural venous sinus thrombosis with venous filling defects, extra- or intracranial abscess formation with a rim-enhancing collection, or meningitis with leptomeningeal enhancement5 (Fig 1b). Furthermore, petrous apex spread may result in bonedestructive petrous apicitis. This may cause deep facial pain with abducens nerve palsy, termed Gradenigo’s syndrome, and should not be confused with the asymptomatic finding of trapped residual fluid within the petrous apex air cells.8,10,11 The differential diagnosis includes cholesteatoma, cholesterol granuloma, and in children, Langerhans’ cell histiocytosis (LCH).2e3,12 However, cholesteatoma and cholesterol granuloma are typically associated with chronic otitis.13 Temporal bone LCH exhibits bone destruction, but also soft-tissue masses.12,14 Rarely, sarcoidosis and Wegener’s granulomatosis may also produce osseous destruction,

but are usually multi-organ diseases.15 Paediatric rhabdomyosarcoma may also be considered, although this is usually an extracranial soft-tissue mass with external auditory canal (EAC) extension.5

Necrotizing otitis externa (NOE) NOE, also known as malignant otitis externa, is an uncommon, aggressive infection beginning at the EAC with deep extension to the soft tissues, middle ear, mastoid, and skull base, most commonly caused by Pseudomonas aeruginosa.16e18 Patients are typically elderly diabetic or immunocompromised patients with fevers, otorrhoea, and severe unremitting otalgia. Pseudomonas infection through cartilaginous clefts in the EAC to the skull base can lead to osteomyelitis with lower cranial neuropathies, signifying a worse prognosis.16e18 Histology shows inflammation with granulation tissue, typically at the EAC bone-cartilaginous junction, and, on culture, Pseudomonas, a Gram-negative aerobic bacillus, which causes a necrotizing vasculitis with thrombosis and coagulation tissue necrosis.16,18,19 At CT, there is auricle and EAC soft-tissue inflammation and possible EAC bone erosion, with tympanic and mastoid opacification and

Figure 1 Left-sided acute otitis media in a 6-year-old male patient with fever and poor response to antibiotics. (a) Transverse CT image through the left temporal bone shows complete opacification of the left tympanum and mastoid air cells. Osseous erosions extend to the middle cranial fossa (filled arrow), sigmoid plate (unfilled arrow), and squamous temporal bone (small arrow). (b) Transverse T1W CE-MRI image shows inflammatory enhancement in the left tympanum and mastoid region. Complications include a rim-enhancing abscess in the left temporal lobe (unfilled arrow), extending to overlying soft tissues, and a left sigmoid sinus filling defect (filled arrow) compatible with a venous sinus thrombosis. A normal contrast-enhancing right sigmoid sinus is shown for comparison (small arrow). Please cite this article in press as: Lo ACC, Nemec SF, Opacification of the middle ear and mastoid: imaging findings and clues to differential diagnosis, Clinical Radiology (2014), http://dx.doi.org/10.1016/j.crad.2014.11.014

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destruction (Fig 2a). MRI shows T1-hypointense and T2/ STIR-hyperintense signal, depicting osseous oedematous changes reflecting skull-base osteomyelitis and adjacent soft-tissue inflammation (Fig 2b). Osteomyelitis may involve the stylomastoid foramen with possible facial paralysis; the jugular foramen with lower cranial neuropathies of the IX, X, XI nerves; the hypoglossal canal with XII nerve neuropathy; or the petrous apex affecting cranial nerve VI, with associated cranial nerve MRI contrastenhancement (Fig 2b). Other complications, such as extraor intracranial abscess formation, dural venous sinus thrombosis, or meningitis, may also be detected with CEMRI.18,19 For skull-base osteomyelitis, bone scintigraphy and gallium nuclear medicine studies show increased tracer uptake. Gallium scans or MRI can monitor treatment response depending on ease of access and costs.16 The differential diagnosis includes processes, such as an EAC squamous cell carcinoma, osteoradionecrosis, or rarely, an inflammatory pseudotumour of the temporal bone.18,20 EAC squamous cell carcinoma can produce focal or diffuse contrast-enhancing soft tissue with bone destruction; however, skin ulceration can usually be seen, often with local nodal metastases.18 Osteoradionecrosis may produce softtissue thickening and bone destruction, months to years after radiotherapy treatment.21,22 Inflammatory pseudotumour (diagnosis of exclusion) is an exceedingly rare, osteodestructive fibroblastic soft-tissue mass of low MR T2W signal exhibiting avid contrast-enhancement.20,23

Histology shows granulation tissue and hyperplastic mucosa.25 On CT, granulation tissue deposition and longterm inflammatory damage translates into tympanic opacification with possible ossicular disruption, mastoid trabeculae thickening, sclerosis, and mastoid cell obliteration8,25 (Fig 3a). The normal ossicular chain includes the highly recognizable “ice-cream cone” on axial CT images, consisting of the malleus head as the “ice cream” and the short process of the incus as the “cone”.3 In COM, tympanic membrane thickening and retraction is common, with possible erosions of the “cone”, long process of the incus, and fibrous involvement of the incudostapedial joint producing apparent joint widening.8 Common complications include post-inflammatory ossicular fixation with fibrous tissue fixation seen as added soft-tissue fibres; acquired cholesteatoma seen as added soft tissue producing ossicular and/or tympanic wall destruction; or tympanosclerosis appearing as tympanic ossification24,27e29 (Figs 3b, 4aeb). CE-MRI is well suited to assess rare complications, such as labyrinthitis, dural venous sinus thrombosis, intracranial abscess formation, or meningitis.2,3,5 The differential diagnosis includes conditions such as a cholesteatoma or cholesterol granuloma.2 Despite showing similar opacification, a cholesteatoma has high DWI (diffusion-weighted imaging) MRI signal, and a cholesterol granuloma shows high T1W change.13 Note, a middle ear and mastoid effusion may be secondary to Eustachian tube obstruction from a nasopharyngeal neoplasm.24

Chronic otomastoiditis (COM) Tympanosclerosis COM is a common disease characterized by tympanic inflammatory tissue with mastoid involvement, secondary to Eustachian tube dysfunction or as a sequela of AOM.2,24,25 Patients may have conductive hearing loss, otorrhoea, tympanic membrane perforation, retraction, and/or visualized scarring at otoscopy.8,25,26

Tympanosclerosis is a chronic reactive process characterized by calcific plaque deposition within the tympanic cavity, reported in 10e30% adults with underlying COM.2,30 Patients may be asymptomatic or have conductive hearing loss from ossicular chain encasement and fixation.2,31

Figure 2 Right-sided necrotizing otitis in a 68-year-old man with type II diabetes and facial nerve palsy. (a) Transverse CT image through the right temporal bone shows confluent mastoid air-cell opacification with irregular bone destruction (arrow) also involving the expected region of the descending facial nerve. (b) Transverse T1W CE-MRI image shows osseous inflammatory enhancement indicating skull-base osteomyelitis with marked soft-tissue involvement (filled black arrow). Soft-tissue inflammatory changes extend through the carotid space to the right parapharyngeal space (filled white arrow). Please cite this article in press as: Lo ACC, Nemec SF, Opacification of the middle ear and mastoid: imaging findings and clues to differential diagnosis, Clinical Radiology (2014), http://dx.doi.org/10.1016/j.crad.2014.11.014

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Figure 3 Appearances and sequelae of chronic otomastoiditis. (a) Left-sided chronic otomastoiditis in a 60-year-old man with recurrent ear infections and bilateral conductive hearing loss. Transverse CT image shows partial circumferential opacification of the left middle ear cavity (filled arrow) and diffusely thickened and sclerotic mastoid air cell trabeculae (unfilled arrow). (b) Tympanosclerosis of the left middle ear cavity in a 70-year-old woman with conductive hearing loss. Coronal CT image through the left temporal bone shows added calcification (arrow) that mimics an “extra ossicle” in the tympanic cavity below the normal incus and malleus. (c) Cholesterol granuloma of the right middle ear in a 22year-old woman with recurrent otitis media, conductive hearing loss, and a “blue” tympanic membrane. Transverse CT image of the right temporal bone shows a soft-tissue density causing complete opacification of the right tympanum and mastoid antrum (arrow). (d) Same patient as (c) T1W unenhanced MRI image through the right temporal bone shows high T1 signal (arrow) in the same location and configuration as on the CT findings.

Histology shows abnormal collagen deposition, resulting in plaques formed by calcium and phosphate crystal deposition.30,32 CT is the preferred imaging method showing punctate or web-like non-enhancing calcific densities, which may mimic “extra ossicles” that can extend to involve the tympanic membrane29,30,32 (Fig 3b). Involvement of the crura of the stapes manifests as a “too well seen” stapes and due to underlying COM, residual debris in the middle ear cavity can also be seen.28,32 Sole tympanic membrane involvement is termed myringosclerosis.30,31 The differential diagnosis includes otitis media, cholesteatoma, or, rarely, a facial nerve venous malformation. Otitis media, however, exhibits no calcification but may contain fluid levels.29 A cholesteatoma is also not calcified but can produce tympanic erosions and otic capsule fistulas.6 A facial nerve venous malformation is a contrast-enhancing lesion, typically with a calcified “honeycomb” matrix.8,29,33,34 Note, the term tympanosclerosis should not be confused with otosclerosis (otospongiosis), which occurs at the oval window and/or cochlea, and produces no tympanic soft-tissue opacification.35

Cholesterol granuloma of the middle ear A cholesterol granuloma is a relatively uncommon lesion characterized by accumulation of blood products and

cholesterol, with reactive granulation tissue formation mostly from a background of COM.13,36 Underlying obstruction from inflammation causing negative pressure build-up leading to mucosal injury and recurrent microhaemorrhage is suspected.13,36 Patients typically are painfree but may present with conductive hearing loss and haemotympanum with a “blue” tympanic membrane.8,37 Histopathological analysis typically shows cholesterol crystals with haemosiderin-laden macrophages and extensive granulation tissue.13,36,37 At CT, a tympanic softtissue lesion is seen, with larger lesions producing smooth expansile scalloping of the surrounding bone and/or ossicular displacement or erosion2,8 (Fig 3c). MRI shows a noncontrast-enhancing high T1W and high T2W signal lesion without diffusion restriction (Fig 3d). Areas of heterogeneity or low T2W signal can be seen due to haemosiderin deposition. MRI signal characteristics are identical to the petrous apex cholesterol granuloma, which usually exhibits more osseous expansion on CT.3,8,31 The differential diagnosis includes conditions such as COM, cholesteatoma, glomus tympanicum tumour, and post-traumatic change.2 COM, however, produces nonhaemorrhagic changes, cholesteatoma shows hypointense T1W signal, and a glomus tympanicum tumour shows avid contrast-enhancement.8,25,38 Although post-traumatic

Please cite this article in press as: Lo ACC, Nemec SF, Opacification of the middle ear and mastoid: imaging findings and clues to differential diagnosis, Clinical Radiology (2014), http://dx.doi.org/10.1016/j.crad.2014.11.014

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Figure 4 Spectrum of cholesteatomas. (a) Right-sided pars flaccida cholesteatoma in a 48-year-old man with conductive hearing loss and a retracted tympanic membrane on otoscopy. Coronal CT image through the right temporal bone shows a rounded soft-tissue lesion in the epitympanum (unfilled large arrow) with marked erosion of the malleolar head and incus. Severe blunting of the scutum bordering Prussak space is seen (small filled arrow). (b) Left-sided pars tensa cholesteatoma in a 48-year-old man with conductive hearing loss and vertigo. Transverse CT image through the left temporal bone shows tympanic opacification with complete ossicular destruction (unfilled arrow), mastoid opacification, and erosions with a resultant perilymphatic fistula at the cochlear apex (small filled arrow). (c) Right-sided congenital cholesteatoma in a 3-year-old male patient with conductive hearing loss, otorrhoea, an intact tympanic membrane and no history of otitis media. Transverse CT image through the right temporal bone shows a soft-tissue lesion in the middle ear with ossicular erosion (small filled arrow) and an expansile soft-tissue lesion in the adjacent mastoid (unfilled arrow). (d) Left-sided cholesteatoma recurrence in a 50-year-old man postmastoidectomy. Transverse CT image through the left temporal bone shows a rounded soft-tissue lesion in the mastoidectomy cavity (arrow) and mastoid cell opacification posteriorly. (e) Same patient as (d). Coronal MRI DWI image (non-echo-planar; b-value ¼ 1000) shows high DWI signal due to restricted diffusion in the same region (unfilled arrow). Adjacent magnetic susceptibility artefact lies at the brain/bone interface (small filled arrow).

changes can cause tympanic density from blood products, a history of recent trauma will be apparent.

Cholesteatoma Cholesteatoma of the middle ear is a benign, nonneoplastic but proliferating lesion, characterized by keratin debris accumulation within a sac of stratified squamous epithelium.6,38,39 They may be acquired (98%), usually secondary to chronic inflammation, or rarely, may be congenital, otherwise known as an “epidermoid” arising from aberrant epithelial rests in the middle ear (2%).6,38,40 Congenital cholesteatomas occur in children or young adults with an intact tympanic membrane and no history of otitis. These patients may be asymptomatic or exhibit hearing loss, otorrhoea, or a white “pearly” lesion in the anterior superior middle ear quadrant on otoscopy.41e43 Patients with acquired cholesteatoma are older, typically adolescents or adults with a history of recurrent ear disease, a visible “pearly” lesion discoloured by inflammatory changes at otoscopy, and/or a perforated tympanic membrane. They can present with conductive hearing loss,

chronic ear discharge, or vertigo.6 There may be progression to erosion of the ossicular chain, scutum, lateral semicircular canal, and tegmen tympani6,42 (Fig 4aeb). Despite surgical therapy, cholesteatoma recurrence is reportedly between 5e20%, with residual rates reported up to 40%.44,45 Histology shows exfoliated keratin within stratified squamous epithelium, cholesterol crystals with chronic inflammation and granulation tissue.46 Pars flaccida cholesteatomas, the most common type of acquired cholesteatoma, arise at the superior pars flaccida portion of the tympanic membrane, and involve the lateral epitympanic recess or Prussak space (Fig 4a). At CT, these classically displace the malleolar head and body of the incus medially and erode the adjacent bony scutum and ossicles2,4 (Fig 4a). Further epitympanic extension can erode the tegmen tympani, potentially risking intracranial extension. Posterolateral extension into the mastoid antrum or facial canal can produce mastoid bone destruction.6 The less common pars tensa cholesteatomas occur at the posterior mesotympanum by the sinus tympani and facial nerve recess. At CT, these demonstrate extension to the medial

Please cite this article in press as: Lo ACC, Nemec SF, Opacification of the middle ear and mastoid: imaging findings and clues to differential diagnosis, Clinical Radiology (2014), http://dx.doi.org/10.1016/j.crad.2014.11.014

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Neoplastic diseases (Table 2)

lesion on otoscopy.51e53 Symptoms from excessive catecholamine secretion occur more commonly in paragangliomas originating in the thorax and abdomen.52 Histology shows a biphasic pattern of chief cells and sustenacular cells surrounded by a fibrovascular stroma, arranged in nests of cells termed “Zellballen”.51 In a glomus tympanicum tumour, CT and MRI show a small (typically millimetres to <2 cm) contrast-enhancing focal mass usually arising at the cochlear promontory from Jacobson nerve glomus bodies (Fig 5aeb). The ossicular chain may be enveloped, but, at CT, bony erosion is usually not seen unless the lesion is large.51,54 In a glomus jugulotympanicum tumour, CT imaging typically shows a poorly defined, avidly contrast-enhancing mass with “permeativeedestructive” or “moth-eaten” bony destruction, originating from a glomus jugulare, with superolateral tympanic spread and possible ossicular chain destruction (Fig 5c).51,52 Jugular fossa expansion, ICA wall dehiscence, or internal jugular vein infiltration may also occur.51 At MRI, lesions are of low T1W and high T2W signal and intense contrast-enhancement is typical (Fig 5d). Lesions >2 cm may show a classic “salt and pepper” appearance on T1W and T2W MRI sequences; however, this is not always present. The hyperintense “salt” refers to haemorrhage or slow flow, and “pepper” refers to hypointense arterial flow voids (Fig 5d).51 Dynamic MRI angiography as well as conventional angiography (which is used for tumour embolization) shows a hypervascular rapid tumour blush and early draining veins.51 There is increased octreotide uptake on scintigraphy, and 18F-fluorodopa and 68Ga-labeled somatostatin analog uptake on PET or PET-CT.53,55 The differential diagnosis of a glomus tympanicum includes an aberrant ICA and a facial nerve schwannoma (detailed in subsequent sections); and for a glomus jugulotympanicum tumour, a jugular foramen schwannoma, a meningioma, an endolymphatic sac tumour, and metastases.54,56,57 However, schwannomas from the IX, X, or XI cranial nerves appear fusiform, extending superomedially with smooth jugular foramen expansion.54,58 Meningiomas may show a dural tail, contain internal calcifications, or produce hyperostosis.54,59 An endolymphatic sac tumour is a rare, osteodestructive tumour with intratumoural spicules and avid contrast-enhancement, arising in the endolymphatic sac or duct sporadically or from von HippeleLindau disease.60e62 Osteodestructive metastases, usually from lung, breast, or prostate cancer, however, lack the degree of high T2 MR signal and/or the internal flow voids.54

Glomus tympanicum and jugulotympanicum

Facial nerve schwannoma

A paraganglioma of the head and neck is a benign, highly vascular tumour arising from the extra-adrenal neuroendocrine system, characterized by neurosecretory granules.50 Paragangliomas originating in the middle ear and jugular fossa are called glomus tympanicum and glomus jugulare tumours, respectively, and glomus jugulotympanicum is used for tumours involving the middle ear and jugular fossa.8,51,52 Lesions may be sporadic or familial, with an adult female predominance, and present with pulsatile tinnitus, hearing loss, vertigo, or visualization of a “red” middle ear

Intratemporal (distal to the internal acoustic canal fundus) facial nerve schwannoma is a rare, benign, slowgrowing lesion characterized by Schwann cell origin.63 Lesions most frequently occur at the geniculate ganglion and commonly span multiple facial nerve segments.57,64 Most patients are middle-aged with varying degrees of facial paresis, tinnitus, or hemifacial spasm.63,65 Conductive hearing loss is common due to ossicular chain involvement in tympanic lesions, whereas sensorineural hearing loss is found in internal auditory canal lesions. Rarely, extension to

epitympanic space with lateral ossicular displacement and ossicular erosion initially along the medial margins4 (Fig 4b). This medial extension leads to contact with the lateral semicircular canal, with possible erosion and fistula formation2 (Fig 4b). Mural and EAC cholesteatomas are other rare forms of acquired cholesteatoma. A mural cholesteatoma produces extensive middle ear and mastoid destruction with EAC wall dehiscence and central matrix extrusion. The resultant cavity lined by a residual rind of cholesteatoma imitates that of a surgical mastoidectomy defect, termed an “automastoidectomy”.6 An EAC cholesteatoma is characterized by an EAC soft-tissue mass with bone erosion of the osseous EAC.47,48 In congenital cholesteatoma, CT shows a rather smooth, well-defined, soft-tissue density lesion in the anterosuperior quadrant of the middle ear cavity in the presence of a normal tympanic membrane (Fig 4c). Lateral semicircular canal, tegmen tympani, and ossicular erosion may be seen, especially involving the long process of the incus and the stapes; however, bone erosion is less common than in acquired cholesteatoma40 (Fig 4c). MRI shows a lesion of low T1W and intermediate to high T2W signal, which may have adjacent trapped secretions of a higher T2 signal. CE-MRI may show rim enhancement secondary to granulation or scar tissue.4,6 Notably, cholesteatomas show high DWI signal due to restricted diffusion.38 Therefore postoperatively, DWI is able to differentiate residual or recurrent cholesteatomas from granulation or scar tissue, which show no restricted diffusion, allowing detection of cholesteatomas smaller than 5 mm with recent MRI DWI techniques4,46 (Fig 4dee). Thus DWI may be sufficient, replacing second-look surgery in patients with prior cholesteatoma resection.49 Rare complications, such as labyrinthitis with inner ear contrastenhancement, dural venous sinus infiltration, intracranial invasion, meningitis, or intracranial abscesses, can be readily assessed on CE-MRI.6 The differential diagnosis includes conditions such as COM, cholesterol granuloma, or a glomus tympanicum tumour.2,6 These, however, exhibit no MRI diffusion restriction. In addition, a glomus tympanicum tumour is usually centred on the cochlear promontory with avid contrast enhancement.25,44,50,51

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Figure 5 Glomus tympanicum and jugulotympanicum tumours. (a) Left-sided glomus tympanicum tumour in a 50-year-old woman with conductive hearing loss, pulsatile tinnitus, and vertigo. Transverse CT image through the left temporal bone shows a focal, rounded soft-tissue lesion centred at the cochlear promontory (arrow). (b) Same patient as (a). Coronal dynamic MRI angiography image shows a hypervascular tumour blush (arrow) in the same location as on the CT findings. (c) Right-sided glomus jugulotympanicum tumour in a 47-year-old woman with conductive hearing loss, pulsatile tinnitus, and dysphagia. Transverse CT image through the right temporal bone shows ill-defined lytic bone destruction extending from the jugular foramen to the mastoid air cells (unfilled arrow) with continuation into the middle ear cavity (filled arrow). (d) Same patient as (c). Transverse T1W CE MRI image shows avid contrast-enhancement of the lesion (arrow) with intralesional “salt and pepper” appearances, referring to punctuate hyperintense haemorrhage or slow flow, and hypointense arterial flow voids.

the greater superficial petrosal nerve may lead to ocular dryness from lacrimation loss.63 Histology shows an encapsulated lesion containing Schwann cells with possible internal cystic changes.63 CT shows a soft-tissue lesion producing smooth “benign” bony expansion along the facial nerve course65 (Fig 6). MRI shows a well-defined, contrast-enhancing lesion of intermediate to low T1W and high T2W signal, which may contain foci of high T2W cystic change. A geniculate ganglion lesion is rounded and may protrude into the labyrinthine segment or extend into the middle cranial fossa. A tympanic segment lesion can be fusiform or multilobulate, and may displace ossicles or even erode the lateral semicircular canal. A mastoid segment lesion can appear ill defined if there is adjacent mastoid air cell extension. A multiple-segment lesion can be tubular or “dumbbell” shaped57,65 (Fig 6). The differential diagnosis includes a facial nerve venous malformation (detailed in the subsequent section) or perineural extension of malignancy.65 Malignant perineural tumour spread shows nerve contrast-enhancement and enlargement, possibly with neuroforaminal destruction and skip lesions.66 Note Bell’s palsy, characterized by rapid facial nerve paralysis with spontaneous clinical improvement,

Figure 6 Left-sided facial nerve schwannoma in a 45-year-old woman with sensorineural hearing loss, vertigo, and partial facial nerve palsy. Transverse CT image through the left temporal bone shows a well-defined tubular lesion in the middle ear cavity, extending from the facial nerve geniculate ganglion to the tympanic facial nerve portion (arrow).

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may exhibit linear, enhancement.8

non-neoplastic

nerve

contrast-

Middle ear adenoma Adenoma of the middle ear is a very rare, benign, slowgrowing lesion characterized by both epithelial and neuroendocrine elements originating from modified respiratory mucosa of the middle ear lining.67e70 Rarely, this tumour may progress to a malignant adenocarcinoma.68,69 The average patient is 45 years old, with a typical presentation of conductive hearing loss, a sensation of aural fullness, and occasionally tinnitus; rarely, sensorineural hearing loss and facial nerve dysfunction may occur.31,69 Histologically, adenomas are poorly vascularized fibrous lesions with chromatin-containing cells that require analysis for neuroendocrine differentiation.68,69,71 At CT, this tumour translates into a non-specific small (usually <3 cm) focal soft-tissue lesion, typically without bone invasion68 (Fig 7). MRI shows a T1-hypointense, T2-hyperintense lesion with contrast enhancement.8,67 Focal tracer uptake in somatostatin-receptor PET/CT may be seen due to neuroendocrine differentiation.72 The differential diagnosis includes tympanic soft-tissue changes, such as COM or cholesteatoma, and tumours such as a glomus tympanicum tumour or a facial nerve schwannoma as described in the above sections.6,8,65,68

Vascular conditions (Table 3) Aberrant ICA The aberrant ICA is a rare congenital vascular anomaly secondary to an underdeveloped ICA cervical segment. This results in a collateral pathway with an enlarged inferior

Figure 7 Right-sided middle ear adenoma in a 57-year-old man with conductive hearing loss and tinnitus. Transverse CT image through the right temporal bone shows a focal, non-specific soft-tissue lesion in the middle ear cavity (arrow).

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tympanic artery coursing into the tympanic cavity through an expanded inferior tympanic canaliculus.56,73,74 A congenital persistent stapedial artery, with resultant absence of the foramen spinosum, may also coexist.74,75 Patients may be asymptomatic or have pulsatile tinnitus or conductive hearing loss.73 Consequences may be severe if an aberrant vessel, otoscopically appearing as a reddish middle ear lesion, is mistaken for a glomus tympanicum tumour and subsequently biopsied.73 On CT, the aberrant ICA is seen as a tubular structure coursing horizontally from posterior to anterior through the middle ear hypotympanum and crossing the cochlea promontory (Fig 8a). Continuity with the distal ICA in the horizontal carotid canal through a carotid plate dehiscence is well-visualized with CT angiography. CT and MR angiography typically show a more lateral course of the aberrant ICA compared to the normal ICA course31,56 (Fig 8b). The differential diagnosis otoscopically includes a glomus tympanicum tumour or anomalies such as a dehiscent jugular bulb or a jugular bulb diverticulum.56,73 A glomus tumour, however, has no continuity with the carotid canal.51 A dehiscent jugular bulb exhibits continuity with the superolateral jugular bulb with an absent intervening sigmoid plate; and a jugular bulb diverticulum is a focal jugular bulb protrusion.76e78

Facial nerve venous malformation (facial nerve haemangioma) Facial nerve venous malformation is a rare, benign, developmental lesion primarily found in adults, arising from vascular plexuses adjacent to the facial nerve, characterized by dilated and ectatic vascular channels.33,34,79 This entity is also commonly called facial nerve haemangioma.34 Patient presentation can mimic an atypical Bell’s palsy with facial nerve dysfunction, such as hemifacial spasm, facial paresis, or paralysis.33,79 Even small (<10 mm) lesions may produce severe functional loss due to either pressure or a “vascular steal” phenomenon with secondary nerve ischaemia.33,34 Histologically, a facial nerve haemangioma shows dilated vascular channels with no internal elastic laminae and possible internal lamellar bone. Negative immunohistochemical staining for haemangioma markers confirms the diagnosis.33,34 With regard to the “ossifiying haemangioma”, classic CT appearances include an expansile, poorly defined lesion (usually <2 cm) along the facial nerve, predominantly at the geniculate ganglion containing internal bone spicules producing a “honeycomb” matrix80,81 (Fig 8c). At MRI, the lesion is of high T2W, high FLAIR and mixed T1W signal with avid contrast-enhancement. Low T1W and T2W signal foci are seen with internal ossification.79,81 The differential diagnosis includes facial nerve schwannomas, perineural tumour spread, or meningiomas.8,33,65 Schwannomas, however, may exhibit a tubular appearance with a smoothly expanded nerve canal.65 Malignant perineural tumour spread shows nerve contrast enhancement and enlargement with possible neuroforaminal

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Figure 8 Vascular conditions of the middle ear. (a) Right-sided aberrant ICA in a 20-year-old man with pulsatile tinnitus. Transverse noncontrast CT image through the right temporal bone shows an elongated tubular structure extending from posteriorly to anteriorly within the middle ear cavity (large unfilled arrow), passing over the cochlear promontory and into the horizontal portion of the carotid canal (small filled arrow). (b) Coronal MR angiography image shows a lateralized right ICA (arrow) with a normal left ICA. (c) Left-sided facial nerve venous malformation (facial nerve haemangioma) in a 35-year-old woman referred with atypical Bell’s palsy. Transverse CT image through the left temporal bone shows a classic poorly defined, expansile lesion containing ossifying matrix at the geniculate ganglion (white arrow), with extension to the tympanic facial nerve portion (black arrow).

destruction. Although temporal bone meningiomas may contain internal calcification, their tympanic involvement is via secondary spread from the jugular foramen, internal auditory canal, or tegmen tympani.33,50,79,82

Fibro-osseous disease (Table 4) Fibrous dysplasia of the temporal bone Fibrous dysplasia is a benign, progressive, primary bone disorder characterized by disordered osteoblastic activity and replacement of normal bone by immature woven bone and fibrous tissue.83e88 Craniofacial fibrous dysplasia with possible temporal bone involvement is one subtype in addition to the monostotic (most common) and polyostotic (30%) type. Rarely, fibrous dysplasia can be due to McCuneeAlbright syndrome.84,86,89 Most patients are under age 30 and present with a progressive focal deformity, conductive hearing loss, or recurrent otitis media due to EAC stenosis.84,86,89 Disease growth usually ceases after puberty or by age 25.87 Histology shows irregular trabeculae of woven bone in a background of connective tissue stroma. The amount of osseous and fibrous content correlates well with the degree of respective sclerotic and cystic changes on imaging.83,86 CT classically shows a well-circumscribed expansile “ground-glass” lesion conforming to the general osseous configuration (Fig 9). Three imaging patterns are described: “Pagetoid” (50%) with bony expansion and mixed areas of opacity and lucency; “sclerotic” (25%) with bone expansion and homogeneous “ground glass; ” and “cyst-like” (25%) with round lucencies and sclerotic borders.83 Mastoid cell obliteration, tympanic cavity encroachment, and EAC stenosis from increased bone thickness are common, and there may be temporomandibular joint involvement whereas otic capsule involvement is rare (Fig 9). Other complications

include cranial nerve neuropathies from jugular fossa encroachment and facial nerve neuropathy from facial canal involvement.83,84 On MRI, fibrous dysplasia may resemble a tumour with T1-hypointense and T2-varied signal. Foci of bone marrow formation may show T1-hyperintense signal, cystic changes or metabolically active tissue exhibit T2hyperintense signal, whereas the T2-hypointense signal corresponds to ossific changes.88,89 Contrast-enhancement depends on the amount of fibrous tissue vascularization.89 Lesions show variable uptake on bone scintigraphy and FDG PET.90 The differential diagnosis includes osteosclerotic conditions, such as Paget’s disease, meningioma, and metastases.87 Paget’s disease, however, occurs predominantly in

Figure 9 Fibrous dysplasia of the right temporal bone in a 19-yearold woman with focal deformity and conductive hearing loss. Transverse CT image through the right temporal bone shows diffuse expansile ground-glass bony changes with marked encroachment upon the middle ear cavity (unfilled arrow). The otic capsule, including the cochlea is preserved (filled arrow).

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Figure 10 Temporal bone trauma with fracture. (a) Longitudinal otic capsule-sparing fracture of the left temporal bone in a 28-year-old man with pain and conductive hearing loss following assault. Transverse CT image through the left temporal bone shows a fracture line (unfilled arrow) extending through the longitudinal petrous bone axis with mastoid cell opacification and trabecular disruption. There is ossicular dislocation, with the incus (not seen) due to complete displacement from the malleus head (filled arrow) and absence of the expected “ice-cream cone” sign. (b) Otic capsule-violating fracture of the right temporal bone in a 34-year-old man with otorrhoea and haemotympanum after a motor vehicle accident. Coronal CT image through the right temporal bone shows a fracture (large unfilled arrow) extending through the labyrinthine structures with pneumolabyrinth (large filled arrow) and tympanic opacification (small arrow) from blood product.

elderly men with serum alkaline phosphatase elevation and shows typical inner calvarial table thickening, diploic space enlargement, “cotton wool” appearances (mixed lysis and sclerosis), and otic capsule involvement.91,92 An intraosseous meningioma may produce hyperostosis; however, enhancing dura is usually seen, as well as permeativeesclerotic bone changes.82 Metastases, such as from prostate or breast carcinoma, are often multiple, show contrastenhancement, and commonly exhibit poorly defined infiltrating margins.93

Traumatic changes (Table 4) Temporal bone trauma with fracture Temporal bone trauma with fracture is typically from high-energy forces, such as motor vehicle crashes (45%), falls (32%), and assault (12%), producing haemorrhagic middle ear and mastoid opacification.94 Patients, predominantly male, can present with EAC blood product, periauricular swelling, and ecchymosis or a “battle sign,” haemotympanum, vertigo, conductive or sensorineural hearing loss, facial nerve dysfunction, cerebrospinal fluid (CSF) leak, and pain.94,95 Around 20% of patients with a skull-base fracture also sustain a temporal bone fracture.94 CT findings include tympanic and mastoid high-density opacification with fluid levels caused by haemorrhage, possible temporal bone fractures with ossicular chain fracture and/or dislocation, air within the labyrinth (pneumolabyrinth), perilymphatic fistulas, and intra- or extracranial gas collections.94 Fractures are traditionally classified in relation to the petrous bone long axis, with longitudinal fractures (70e90%) often associated with ossicular disruption and transverse fractures (10e30%) often producing pneumolabyrinth and/or facial nerve injury94,95 (Fig 10a). A newer classification describes otic capsule-violating

(5e20%) or -sparing fractures.96 In otic capsule-violating fractures, the cochlea, semicircular canals, or vestibule are injured, with an increased association of facial nerve injury, sensorineural hearing loss, and CSF leak (Fig 10b). Ossicular chain dislocation (most commonly at the incudostapedial joint) occurs more often than ossicular fractures94 (Fig 10a). CT angiography can evaluate vascular complications, such as dissection, occlusion, or ICA pseudoaneurysm formation.94 MRI may show high T1W and T2W signal blood product within the tympanic cavity, and/or haemolabyrinth or pneumolabyrinth producing loss of expected high T2W labyrinthine signal due to optic capsule fracture. MRI can assess acute complications, such as facial nerve injury with contrast-enhancement of the nerve or arterial dissection, with a possible high T1W fat-suppressed intramural haematoma.97 The differential diagnosis includes conditions producing haemorrhagic opacification, including a cholesterol granuloma or otitis, however, the lack of trauma is obvious. Moreover, normal skull sutures/fissures, such as the tympanosquamous, petrotympanic, and the occipitomastoid suture may mimic fractures, but these are usually symmetrical, sclerotic, and well-corticated.98

Conclusion Assessed in conjunction with the clinical presentation, subtle patterns of middle ear and mastoid opacification on CT and MRI provide guidance towards formulating the correct diagnosis.

Acknowledgements The authors would like to thank Ms Mary McAllister (Johns Hopkins University, Baltimore, Maryland) for her

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help in editing the manuscript. The authors would also like to thank Professor Dr. Christian Czerny (Medical University of Vienna, Vienna, Austria) for his help in image preparation.

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Please cite this article in press as: Lo ACC, Nemec SF, Opacification of the middle ear and mastoid: imaging findings and clues to differential diagnosis, Clinical Radiology (2014), http://dx.doi.org/10.1016/j.crad.2014.11.014