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Imaging of middle ear pathology
Imaging of Middle Ear Pathology Francis Veillon, Sophie Riehm, Marie-No,lie Roedlich, Phillippe Meriot, Emmanuel Blonde, and Jean Tongio
HE IMAGING of the middle ear is built on computed tomography (CT) and magnetic resonance imaging (MRI) usually in chronic otitis media. With serous otitis media or hyperplasia there is no need of imaging. In contrary, mastoiditis aggressive hyperplasia and cholesteatoma need CT for evaluating the extension of the lesions. MRI is needed when expecting a cholesterol granuloma, a meningeal protrusion in the tympanic cavity, or in case of lateral semicircular canal erosion. In postoperative patients, CT (sometimes with MRI) is performed for the diagnosis and location of a recurrent cholesteatoma. In malformations of the middle ear CT can assess the size of the tympanic cavity, the presence of the ossicles, windows, and the position of the facial nerve canal and a possible association with a primitive cholesteatoma. In trauma, CT demonstrates the fracture, lesions of the ossicles and of the windows; MRI will be performed in meningeal protrusion and traumatic facial palsies. For all the possible tumors of the middle ear, CT and MRI have to be performed.
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TECHNICAL PRACTICE IN MIDDLE EAR IMAGING: CT AND MRI
CT It is possible to use two procedures with CT: spiral and nonspiral. The first technique is useful for all the middle ear and most of the pathologies except nonoperated otosclerosis. Sections of 0.5 mm are now possible with an increment of 0.3 mm allowing nice reconstructed views of all the planes in the temporal bones nearly equivalent to direct sections. Nonspiral CT is reserved for the examination of the footplate because of the better spatial resolution allowing good results in otosclerosis but also in malformations and traumatic lesions. A study in an axial plane (parallel to the tragusnasion line) should always be accompanied by coroval sections. The sagittal view is especially
From the Department of Radiology, Hopital de Hautepierre, Strusbourg, France. Address reprint requests to Francis Veillon, MD, Department of Radiology, Hopital de Hautepierre, Avenue Moliere, Strasbourg, France 67098. Copyright 9 2000 by W.B. Saunders Company 0037 198X/00/3501-0002510.00/0 2
interesting for showing the tympanic cavity's roof. This plane is always performed in postoperative patients.
MRI MRI is becoming more and more useful for the middle ear study. It can give information in postoperative patients considering a possible recurrent cholesteatoma. It is also useful for the study of mastoiditis, aggressive otitis, giant secondary cholesteatoma (particularly when it extends to the middle or posterior cranial fossa) and in all kinds of tumors in the tympanic cavities. MRI is also used in pathologies involving both middle and inner ears such as some cholesteatomas and traumatic lesions, particularly with fistulas and malformations. MRI will be performed in a horizontal plane with a T1 spin echo sequence without and with gadolinium injection. A sagittal and/or coronal view in the same sequence after contrast medium injection will complete the study. T2-weighted sequences are not so interesting in the middle ear pathology because most of the lesions are more or less bright. It is nevertheless useful when considering the possibility of a meningocele or a cholesterol granuloma. MR angiography (MRA) is interesting for showing up an abnormal course of the internal carotid artery in the tympanic cavity and a persistence of the stapedial artery. THE CHRONIC OTITIS MEDIA
CT and MRI may be useful and complete the clinical examination in several conditions.
In Emergency Young children and teenagers may be admitted for a history of pain and edema in the mastoi'd region. The radiologist is asked to delineate the extension of the hyperplasia or cholesteatoma in the tympanic cavity and the mastoid cells or to identify osteitis of the tegmen or the posterior wall of the petrous bone which may appear as little defect in the cortical bone. It is also important to evaluate for possible edema and abscess of the middle and posterior cranial fossa and to diagnose as early as possible a partial or total thrombosis of the sigmo~'d sinus. The middle ear in mastoiditis is Seminars in Roentgenology, Vol XXXV, No 1 (January), 2000: pp 2-11
IMAGING OF MIDDLE EAR PATHOLOGY
usually filled up with granulation tissue that appears isodense on CT. This one shows only the aeration of the middle ear and the possible osteitis (Fig 1). A spin-echo (SE) T l - w e i g h t e d sequence in MRI is more useful to demonstrate the mucosa hyperplasia isointense to hyperintense on T l - w e i g h t e d scans because of hyperemia, bright in T1 after Gadolinium injection. If a keratoma is associated, its intermediate signal will contrast with the surrounding bright granulation tissue after contrast medium injection in T I . The main information provided by MRI is the possible extension of the infection to the meninges, temporal lobe, and cerebellum) An M R A must always complete the conventional M R study searching for a thrombosis of the sigmoid sinus even if there is no clinical evidence of this pathology.
Tympanosclerosis Tympanosclerosis is a kind of scar in chronic otitis media. It represents the result of years of inflammation. This pathology may nevertheless be associated with an acute onset of inflammation. Usually there is no need for imaging, but if an associated cholesteatoma is expected CT would be very useful for the diagnosis of the epidermic tissue among the calcified material. Tympanosclerosis is a hyalinization of the middle ear mucosa and appears as calcifications in the tympanic membrane, tendons, ligaments, ossicles, and mucosa of the middle ear. CT demonstrates the amount o f calcifications particularly in the stapes footplate, which is irregular, thickened, and hyper-
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Fig 2. Tympanosclerosis. CT shows calcification of the footplate, which is thickened (arrow).
dense on high-resolution horizontal CT sections (Fig 2). A particular interesting condition is the ossification of the middle ear called osteomatous otitis, which may lead to surgical difficulties when discovered during a tympanic surgery. The middle ear is then more or less filled with bone that may be located in the attic, encroaching on the ossicles, associated or not with a cholesteatoma. CT demonstrates the amount of calcified material, the position and structure of the ossicles, the possible associated keratoma with or without a fistula of a semicircular canal (usually the lateral one).
Aggressive Hyperplasia This entity is not as well known by radiologists. It represents an invasion of the middle ear by granulation tissue, which appears at histological examination as villosities. This pathology may be as aggressive as a cholesteatoma without any presence of an epidermic tissue. A fistula of the cochlea or semicircular canals or erosion of the facial nerve canal with or without facial palsy are possible. CT shows the total filling of the middle ear and the possible defect of its inner wall (Fig 3). MRI demonstrates the absence of any cholesteatoma with an enhancement of the material within the tympanic cavity.
Cholesterol Granuloma
Fig 1. sinus.
Mastoiditis. CT shows thrombosis of the sigmo'id
Cholesterol granuloma is a result of a hemorrhage of the mucosa with a granulation tissue reaction. It may be very small or well developed in the middle ear. The signal is bright on T I and T2 spin-echo sequences. 2
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VEILLON ET AL
ium injection may help arrive at a diagnosis, demonstrating an isointense mass surrounded by a crown of hyperintense tissue related to the peripheral hyperplasia. 7 It is always important to compare in chronic otitis media the results provided by MRI and by CT. The Postoperative Middle Ear in Chronic Otitis Media
Fig 3. Aggressive hyperplasia. CT shows erosion of the canal of the facial nerve (arrow). Tympanosclerosis of the internal attic encroaching on the malleus and incus (curved arrow).
Cholesteatoma The cholesteatoma represents a classic complication of chronic otitis media usually after a perforation in the upper and posterior part of the drum. The epiderm is then allowed to invade the attic. If the otologist is aware of the presence of a cholesteatoma, he does not know its extension and relationships with the facial nerve, the cortical of the inner ear, the tegmen, and the sigmoid sinus. There is a big difference between a pearl of cholesteatoma in the external attic and an cholesteatomatory mass invading the antrum and posterior cranial fossa. The first can be removed in less than l hour, but the second will require an operation of 6 or 7 hours. The clinical otoscopical appearance may be the same. The keratoma appears as a mass more or less round shaped in the attic. 3,4 It can spread in the middle ear with usually spherical margins (Fig 4). Sometimes most of the epidermoid tissue has been evacuated and persists only as a destruction of the walls without any CT content in the tympanic cavity. When the extension of the cholesteatoma is suspected to invade the middle or posterior cranial fossa, MRI will demonstrate the relationship of the mass to the dura mater. 5 The dura is usually not destroyed but compressed by the mass. Cholesteatomas appears isointense on Tl-weighted, slightly white on T2-weighted scans, with no contrast enhancement after Gadolinium 6 injection. Fat saturation may be helpful when injecting contrast medium. In some doubtful cases, MRI may be useful particularly when soft tissue fills up the totality of the tympanic cavity without significant bony destructions. MRI with and without Gadolin-
There are two kinds of surgical techniques approaching the middle ear: the first one preserves the external auditory canal; in the second one, the posterior wall of the tympanic bone is removed. There are different variants around these techniques. The first techniques (with the intact external canal wall) for many years has been done in two stages: the first stage consists of removing the keratoma, the second stage after 18 months checks for absence of an epidermic recurrence or rest of cholesteatoma within the tympanic cavity and allows an ossicular reconstruction among a dry ear. If after the first operation there is no clinical evidence of a recurrent cholesteatoma, and hearing has been improved during the first time, CT will be mandatory for deciding whether or not the second operation will be performed. Even if a second look is necessary, CT is useful for evaluating the extension of a possible recurrent cholesteatoma. In our experience we consider the shape of the soft-tissue content within the operated cavity. It is then possible to diagnose, in more than 85% of the
Fig 4. Secondary cholesteatoma. CT shows the mass is developing in the posterior part of the tympanic cavity.
IMAGING OF MIDDLE EAR PATHOLOGY
cases, the presence of a cholesteatoma compared with fibrosis or hyperplasia. CT must be performed in the axial, coronal, and sagittal planes. In scalloped masses with irregular margins, a cholesteatoma is likely. Bowl-shaped masses in the external attic are also related to cholesteatoma. 3 In thin concave limited soft-tissue masses, fibrosis is favored as the diagnosis. With well-defined straight soft-tissue content inflammation or fibrosis should be diagnosed. Tissue covering the periphery of the cavity is usually related to hyperplasia. In cases with doubtful images, MRI should be of some interest using the Tl-weighted scan with and without Gadolinium in an axial and sagittal plane after contrast medium injection. The keratoma appears as an intermediate signal without any contrast enhancement surrounded by enhanced granulation tissue (Fig 5). THE MALFORMATIONS
The malformations of the middle ear are often associated with congenital abnormalities of the external ear. Thus, the absence of the tympanic bone is usually associated with a fusion of the malleus and incus and sometimes a fixation of these ossicles to the lateral wall of the tympanic cavity. The fixation of an ossicle may be the only sign of a malformation. All the parts of the ossicles may be missing, particularly the long process of the incus. This diagnosis is quite easy to make particularly when performing oblique sections of the ossicles perpendicular to the footplate allowing one to
Fig 5. Recurrent cholesteatoma. MRI shows Tl-weighted sequence with Gadolinium injection. The intermediate signal of the cholesteatoma is visible surrounded by a rim of enhancement in the tympanic cavity (curved arrow). The cholesteatoma is also developing in the mastoi'd region (arrow).
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delineate the missing part of the long process of the incus. The fixation of the stapes is more difficult to demonstrate. It is quite important to consider the increased thickness of the footplate associated with some ossicular or wall malformations. The shape of the stapes may be changed, 8 and the tendon of the stapedius may be missing or calcified. CT shows the absence of the stapedius canal close to third portion of the facial nerve canal. The absence of the stapes is easily demonstrated usually associated with a lowering of the tympanic part of the facial nerve (Fig 6). The change in the position of the facial nerve canal is one of the most important pieces of information provided by CT in middle ear malformations. This part of the nerve, 9 normally located above the oval window, should mn in the window itself. The facial nerve is then clearly visible close to the footplate. The little airspace located between the footplate and the facial nerve may disappear in cases of footplate anomalies. The third portion of the facial nerve canal is displaced anteriorly in all the tympanic bone aplasia. The round window is also an important opening to evaluate. It may be small or absent. Its presence must always be considered. Among the walls of the tympanic cavity, the most important to appreciate is the tegmen tympani, which may be lowered, the duramater is usually normal. TRAUMATIC LESIONS OF THE MIDDLE EAR
Fractures of the middle ear are very frequent (80% to 90%) in skull-base trauma. The traumatic wave runs in the middle ear entering the temporal bone through the squamous bone, the tympanic bone, or the posterior part of the petrous bone. The ossicles are then submitted to a force with a possible displacement or fracture. CT is the best examination to appreciate the displacement of the ossicles. ~ The most sensitive ossicle is the incus because of its poor attachments. Reformated CT sections in coronal and sagittal planes give nice views of the injured ossicles. A particular attention must be paid to the stapes: the crus may be broken with a clear conductive hearing loss. The footplate is rarely fractured. It is more often displaced in the vestibule, therefore CT and MRI are very important to analyze the position of the stapes in the inner ear. The perilabyrinthine leakage that occurs through the oval window (center or periphery) depends on the degree of stapes displacement. An air bubble
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Fig 6. Malformation. (A) Malformation of the stapes. CT shows a single crus is visible medially to the long process of the incus (arrow), (B) CT shows absence of the stapes (arrow).
may be demonstrated in the vestibule (Fig 7). Fractures of the round window and the disruption of the round window membrane must also be considered. It has been described in MRI the possibility of a contrast medium enhancement in the region of the round window associated with a fistula of the perilymph. The occipital fracture running in the inner ear usually respects the tympanic cavity (translabyrinthine fractures). They are quite rare (10% of the temporal bone traumatisms). In 5% of the cases, trauma may involve both middle and inner ears. In such cases, a particular attention must be paid to the windows that are often injured by the traumatic wave.
OTOSCLEROSIS Otosclerosis is the development of a spongious bony tissue in the labyrinthine bone particularly in
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the region and vicinity of some cartilaginous nests close to the anterior part of the oval window (fissula antefenestram). The footplate may be invaded by otosclerotic tissue. Usually this disease does not extend beyond the middle layer of the labyrinthine bone, the anterior part of the oval window, and the footplate. In some rare cases the otosclerotic foci may develop in the internal attic or the mesotympanum encroaching on the malleus and the incus (Fig 8). In CT these foci are demonstrated as white or grey bony masses originating in the lateral part of the labyrinthine bone, developed in the medial attic. MRI is useful for analyzing the active or inactive part of the otosclerotic foci within the middle layer of the labyrinthine bone but does not give further information about the development of the lesion in the middle ear. In postoperative patients CT nicely demonstrates
~ ~ 84
Fig 7. Fracture of the temporal bone in the middle ear CT. The fracture is running in the posterior part of the tympanic cavity before reaching the anterior wall (arrows). Air bubble is shown in the vestibule (curved arrow),
Fig 8. Otosclerosis. CT shows development of an otoscierotic focus in the region of the round w i n d o w with protrusion in the tympanic cavity (arrow).
I M A G I N G O F M I D D L E EAR P A T H O L O G Y
Table 1. Middle Ear Pathology and CT Imaging Chronic Otitis Media Spiral
+++
Non spiral +, recommended;
Traumetisms
.
Malformations
+++ .
++++ .
Tumors +++
.
Otosclerosis
Postoperative Otosclerosis
-
+++
+++
+
-, not useful.
the position of the ossicular prothesis extremities: the medial one in the oval window and the lateral one close to the long process of the incus. A subluxation of the prosthesis in the vestibule may be demonstrated by CT. Particular attention must be paid if the distal part of the prosthesis reaches the center of the vestibule. The lateral extremity of the prosthesis may be taken down and separated from the lenticular process. Reformated sections allowed by the spiral CT technique are very nice for demonstrating malposition of the prosthesis. MRI may demonstrate the medial extremity of a dislocated prosthesis. It can also demonstrate a possible labyrinthine granuloma if a high-resolution T2weighted sequence is used. In some cases, the prosthesis is deficient due to incus long process destruction easily delineated by CT (Tables 1 and 2). TUMORS AND PSEUDOTUMORS OF THE MIDDLE EAR
Primitive Cholesteatoma This lesion is made of an epidermal remnant in the mesotympanum usually far from the attic. It may be very small or may be large, invading most of the middle ear. There is no history of chronic otitis media, the drum is normal or malformed. The main clinical sign is a conductive hearing loss with a possible mass detected at the otoscopic examination. J0 CT shows the mass in the mesotympanum without any sign of chronic otitis media (Fig 9). The long process of the incus or the stapes may be
destroyed. MRI is usually of small interest in this field because this lesion rarely invades the inner ear.
Glomustympanicum Tumor It originates in little vascular bodies localized along the Jacobson's nerve course close to the promontory. It may be very small: 1 to 2 mm or extend in the totality of the tympanic cavity. The lesion may extend into the Eustachian tube and the Jacobson's canal. The clinical signs are that of a blue drum with pulsatile tinnitus. CT demonstrates a mass close to the course of the tympanic nerve whose density is enhanced after contrast medium injection. If a serous fluid surrounds the mass the diagnostic may be more difficult. MRI is very useful. On T1 scans with Gadolinium, H the contrast-enhanced mass close to the promontory among the grey signal of the serous fluid is evident (Fig 10). In all the cases, an angiogram is proposed confirming the diagnosis and allowing possible embolization. Invasion of the middle ear is possible by a glomus jugulare tumour originating in the jugular adventice. The extension to the tympanic cavity represents only a part of the tumor centered on the jugular foramen with high signal on Tl-weighted scan after contrast medium injection. There may be small signal void structures corresponding to arterial vessels running into the lesion. The meningeal reaction is usually small.
Table 2. Middle Ear Pathology and MR Imaging Chronic Otitis Media (mastoiditis, aggressive otitis, giant secondary chole)
Traumatisms (facial nerve contusion)
+
++
+++
+ + (meningo-
-
+
+++
T2
+ (cholesterol
+++) -, not useful.
Angio MR
+
-
+ Ho
+++
+, r e c o m m e n d e d ;
Stapedial Artery
-
+ + Ho
T1 + G a d o
granuloma
Postoperative Middle Ear (chole)
Ho
T1
Ho
Malformation
Tumors (clinical context)
cele)
+
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Fig 9. Primitive cholesteatoma. CT shows mass developing in the anterior part of the tympanic cavity close to the malleus (arrow),
The Adenoma In the setting of chronic otitis media the epithelium of the tympanic cavity may produce an adenoma encroaching on the ossicles. CT shows a mass in the middle ear (Fig 11) whose signal in MRI is intermediate in T 1, high after Gadolinium injection. The lesion is not really centered on the Jacobson's nerve canal; a malignant lesion as an adenocarcinoma may give the same presenta-
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Fig 11. Adenoma of the middle ear. CT shows the mass in encroaching on the malleus (arrow).
CT demonstrates a mass in the course of the facial nerve invading the middle ear destroying or not the stapes or the incus. Neuroma of the third portion of the facial nerve m a y extend into the chorda tympani and the middle ear. MRI will show an intermediate signal the mass on Tl-weighted, scans, hyperintense on T2W scans and avidly enhancing involving the facial nerve canal. 13
tion.l,12,t3 Neuroma of the Facial Nerve
Neuroma of the Eighth Nerve
All the parts of the facial nerve may be involved by a neuroma. It may extend in the tympanic cavity through the geniculate ganglion, the tympanic, or mastoid portions. A facial palsy may be present or not. If it is absent, the only sign of the neuroma may be a conductive hearing loss, which could lead to the false diagnosis of an otosclerosis.
Schwannomas of the eighth nerve may extend into the labyrinthine lumen. It may also invade the middle ear through the lateral semicircular canal, the promontory, or the windows particularly the round one. A T l - w e i g h t e d sequence will show the contrast enhancement in the labyrinthine lumen
Fig 10. Glomus tumor of the tympanic cavity MRI (T1weighted sequence) with Gadolinium injection. Mass enhanced in the tympanic cavity (arrow) surrounded by a serous otitis media.
Fig 12. Neuroma of the internal auditory meatus, the labyrinth, extended to the middle ear. MRI shows T1-weighted sequence with Gadolinium injection, The neuroma is very well delineated running from the internal auditory meatus through the internal ear to the middle ear (arrow).
IMAGING OF MIDDLE EAR PATHOLOGY
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and the tympanic cavity (Fig 12). The T2 highresolution sequence will diagnose a mass in the labyrinthine lumen.
Hemangioma Hemangiomas of the facial nerve are well known in the geniculate ganglion but are not as common in the chorda tympani.
Carcinoid Tumor of the Middle Ear This lesion is well known from the otologists and is responsible of a conductive hearing loss. It may be present with a little bulging of the drum, with or without perforation. 14 CT shows up a mass in the tympanic cavity, well marginated, with or without ossicular destruction, highly vascularized with avid Gadolinium enhancement in T 1 after contrast medium injection and a high signal in T2 (Fig 13). The diagnosis is made after the electronic microscopic examination demonstrating intracytoplasmic neuroendocrine granulations. The evolution is not very aggressive.
Fig 14. Meningioma of the posterior wall of the petrous bone extended to the middle ear through the Hyrtl fissure. MRI shows Tl-weighted sequence with Gadolinium injection. The white mass in the middle ear is well delineated (arrow).
to the tympanic cavity on Tl-weighted scan with Gadolinium injection (Fig 14).
Tuberculosis of the Middle Ear
A meningioma may be discovered in the tympanic cavity. It may originate in the cerebellopontine angle, the middle cranial fossa particularly in the meninges close to the geniculate ganglion. There are several ways for the meningioma to reach the tympanic cavity: the Hyrtl fissure, the Eustachian tube, and the tegmen tympani. The only sign of the lesion may be a serous otitis media leading to imaging when it occurs in elderly patients. ~5 CT discovers the sign of a meningioma in the posterior or middle cranial fossa. MRI will delineate the path
Tuberculosis is a rare entity in the tympanic cavity. It may be diagnosed clinically when it extends in the external auditory meatus with the presence of caseum directly analyzed by the otologist. CT shows a soft-tissue mass destroying the ossicles in the tympanic cavity with possible extension to the adjacent regions (middle and posterior cranial fossa). Some geodes may be delineated in the petrous bone; the lesions appear with an intermediate signal in T1, high in T2 with enhancement within the petrous bone and the meninges of the adjacent regions (Fig 15). 16
Fig 13. Carcinoid tumor of the attic. MRI shows T1weighted sequence with Gadolinium injection, An enhanced mass is visible in the lateral part of the attick (arrow),
Fig 15. Tuberculosis of the left petrous bone. MRI shows Tl-weighted sequence with Gadolinium injection,
The Meningioma of the Tympanic Cavity
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Fig 16. Histiocytosis. CT shows destruction of the posterior part of the petrous bone (arrow).
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Fig 18. Acute leukemia of the middle ear. CT shows a soft-tissue mass is developing in the middle part of the tympanic cavity,
Histiocytosis X This granulomatosis is made of histiocytes and eosinophils. In the cytoplasm of the histiocytes, the electron microscopy discovers the presence of a rodshaped inclusion (Birbeck granule). It mainly occurs in children showing evidence of an external and middle ear inflammation, t7 One or several cavities may be discovered by CT particularly in the mastoid region (Fig 16) with, in MRI, an intermediate signal on T1, high on T2 and with a strong contrast enhancement after Gadolinium injection on T1. MRA may show thrombosis of the sigmo'id sinus.
Aneurysm of the Internal Carotid Artery This is a very rare entity often occurring in the postraumatic setting. The mass of the internal carotid petrous canal may obstruct the Eustachian tube or extend in the middle ear. MRA will suggest the correct diagnosis. Any surgical procedure with-
out knowing the presence of this pathology could lead to an injury of the internal carotid artery. THE MALIGNANT TUMORS OF THE MIDDLE EAR
Squamous Cell Carcinoma This lesion is well known in the auricle and the external auditory meatus. It is not so frequent in the tympanic cavity, usually complicating a chronic otitis media. Its development may be very limited or, on the contrary, very aggressive involving the middle cranial fossa, the mastoid, the facial nerve canal, the labyrinth, and the cerebello-pontine angle (Fig 17). There is no specific appearance in MRI: intermediate signal in TI, intermediate signal in T2. The main problem is to delineate the extension to the extension to the adjacent intracranial structures and the possible involvement of the facial nerve.
Fig 17. Squamous cell carcinoma. (A) Carcinoma of the posterior part of the petrous and squamous bone. CT shows destruction of the external cortical bone (arrow). (B) Same case MRI shows Tl-weighted sequence with Gadolinium injection, The mass developing in the middle ear is enhancing after contrast medium injection (arrow).
IMAGING OF MIDDLE EAR PATHOLOGY
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The a d e n o c a r c i n o m a o f the m i d d l e ear has no specific features. M R I and C T will a p p r e c i a t e the e x t e n s i o n o f the lesion. 18
Acute Leukemia
Lymphoma L y m p h o m a is rare in the m i d d l e ear and usually e x t e n d s f r o m the external auditory m e a t u s w i t h o u t any specific sign in C T or M R I . L y m p h o m a m a y e x t e n d f r o m p a r o t i d g l a n d source.
This lesion is not so well k n o w n b y radiologists. It a p p e a r s as a soft tissue within the m i d d l e ear usually a s s o c i a t e d w i t h a p r e s e n c e o f y o u n g specific cells in the l a b y r i n t h i n e l u m e n w i t h o u t b o n y destruction. T h e signal is i n t e r m e d i a t e on T1, high on T2 w i t h o u t any G a d o l i n i u m e n h a n c e m e n t . It looks like i n f l a m m a t i o n , but this entity m u s t be c o n s i d e r e d b y the r a d i o l o g i s t w h e n k n o w i n g the c o n t e x t o f an acute l e u k e m i a (Fig 18).
Metastases M e t a s t a s e s m a y i n v o l v e the m i d d l e ear but in m o s t o f the cases, r e p r e s e n t s an e x t e n s i o n f r o m the b o n y structures o f the p e t r o u s bone. U s u a l l y prim a r y t u m o r s are f r o m the breast, prostate, or lung. M R I is very useful for the e v a l u a t i o n o f an e x t e n s i o n to a d j a c e n t regions.
REFERENCES
1. Casselman JW: Temporal bone imaging. Neuroimaging Clin North Am 6:265-289, 1996 2. Swartz JD, Harnsberger HR, Mukherji SK: The temporal bone. Radiol Clin North Am 36:5, 1998 3. Czemy C, Turetschek K, Duman M, et al: Imaging of the middle ear: CT and MRI. Radiologe 37:945-953, 1997 4. Liu DP, Bergeron RT: Contemporary radiologic imaging in the evaluation of middle ear-attic-antral complex cholesteatomas. Otolaryngol Clin North Am 22:897-909, 1989 5. Kaseff LG, Seidenwurm DJ, Nieberding PH, et al: Magnetic resonance imaging of brain herniation into the middle ear. Am J Otol 13:74-77, 1992 6. De Schepper AJr, Appel B, Crols R: Temporal lobe abscess as a complication of cholesteatoma: Sequential radiological findings. J Belge Radiol 81:87-89, 1998 7. Martin N, Sterkers O, Nahum H: Chronic inflammatory disease of the middle ear cavities: Gd-DTPA-enhanced MR imaging. Radiology 176:399-405, 1990 8. Charachon R, Barthez M, Lavieille JP: Minor malformations of the ear ossicles: New classification and therapeutic results. Ann Otolaryngol Chir Cervicofac 111:69-74, 1994 9. Eelkema EA, Curtin HD: Congenital anomalies of the temporal bone. Semin Ultrasound CT MR 10:195-212, 1989 10. Robert Y, Carcasset S, Rocourt N, et al: Congenital cholesteatoma of the temporal bone: MR findings and comparison with CT. AJNR Am J Neuroradiol 16:755-761, 1995
11. Phelps PD, Lloyd GA: Magnetic resonance with gadolinium DTPA for the investigation of temporal bone tumours. C/in Otolaryngol 14:251-262, 1989 12. Kletzker GR, Smith PG, Mclntire LD, et al: Presentation and management of uncommon lesions of the middle ear. Am J Otol 16:634-642, 1995 13. Mafee MF, Valvassori GE, Kumar A, et al: Tumors and tumor-like conditions of the middle ear and mastoid: Role of CT and MRI. An analysis of 100 cases. Otolaryngol Clin North Am 21:349-375, 1988 14. Blaker H, Dyckhoff G, Weidauer H, et al: Carcinoid tumor of the middle ear in a 28-year-old patient. Pathol Oncol Res 4:40-43, 1998 15. Veillon E Riehm S, Roedlich MN, et al: Imaging of the temporal bone and face (tumors and pseudotumors). Eur Radiol 9:$69-$75, 1999 (suppl 2) 16. Moon WK, Han MH, Chang KH, et al: CT and MR imaging of head and neck tuberculosis. Radiographics 17:391402, 1997 17. Angeli S1, Luxford WN, Lo WW: Magnetic resonance imaging in the evaluation of Langerhans' cell histiocytosis of temporal bone: case report. Otolaryngol Head Neck Surg 114:1204124, 1996 18. Friedman I: Middle ear adenoma and adenocarcinoma. Otolaryngol Head Neck Surg I 11:154, 1994
HE IMAGING of the middle ear is built on computed tomography (CT) and magnetic resonance imaging (MRI) usually in chronic otitis media. With serous otitis media or hyperplasia there is no need of imaging. In contrary, mastoiditis aggressive hyperplasia and cholesteatoma need CT for evaluating the extension of the lesions. MRI is needed when expecting a cholesterol granuloma, a meningeal protrusion in the tympanic cavity, or in case of lateral semicircular canal erosion. In postoperative patients, CT (sometimes with MRI) is performed for the diagnosis and location of a recurrent cholesteatoma. In malformations of the middle ear CT can assess the size of the tympanic cavity, the presence of the ossicles, windows, and the position of the facial nerve canal and a possible association with a primitive cholesteatoma. In trauma, CT demonstrates the fracture, lesions of the ossicles and of the windows; MRI will be performed in meningeal protrusion and traumatic facial palsies. For all the possible tumors of the middle ear, CT and MRI have to be performed.
T
TECHNICAL PRACTICE IN MIDDLE EAR IMAGING: CT AND MRI
CT It is possible to use two procedures with CT: spiral and nonspiral. The first technique is useful for all the middle ear and most of the pathologies except nonoperated otosclerosis. Sections of 0.5 mm are now possible with an increment of 0.3 mm allowing nice reconstructed views of all the planes in the temporal bones nearly equivalent to direct sections. Nonspiral CT is reserved for the examination of the footplate because of the better spatial resolution allowing good results in otosclerosis but also in malformations and traumatic lesions. A study in an axial plane (parallel to the tragusnasion line) should always be accompanied by coroval sections. The sagittal view is especially
From the Department of Radiology, Hopital de Hautepierre, Strusbourg, France. Address reprint requests to Francis Veillon, MD, Department of Radiology, Hopital de Hautepierre, Avenue Moliere, Strasbourg, France 67098. Copyright 9 2000 by W.B. Saunders Company 0037 198X/00/3501-0002510.00/0 2
interesting for showing the tympanic cavity's roof. This plane is always performed in postoperative patients.
MRI MRI is becoming more and more useful for the middle ear study. It can give information in postoperative patients considering a possible recurrent cholesteatoma. It is also useful for the study of mastoiditis, aggressive otitis, giant secondary cholesteatoma (particularly when it extends to the middle or posterior cranial fossa) and in all kinds of tumors in the tympanic cavities. MRI is also used in pathologies involving both middle and inner ears such as some cholesteatomas and traumatic lesions, particularly with fistulas and malformations. MRI will be performed in a horizontal plane with a T1 spin echo sequence without and with gadolinium injection. A sagittal and/or coronal view in the same sequence after contrast medium injection will complete the study. T2-weighted sequences are not so interesting in the middle ear pathology because most of the lesions are more or less bright. It is nevertheless useful when considering the possibility of a meningocele or a cholesterol granuloma. MR angiography (MRA) is interesting for showing up an abnormal course of the internal carotid artery in the tympanic cavity and a persistence of the stapedial artery. THE CHRONIC OTITIS MEDIA
CT and MRI may be useful and complete the clinical examination in several conditions.
In Emergency Young children and teenagers may be admitted for a history of pain and edema in the mastoi'd region. The radiologist is asked to delineate the extension of the hyperplasia or cholesteatoma in the tympanic cavity and the mastoid cells or to identify osteitis of the tegmen or the posterior wall of the petrous bone which may appear as little defect in the cortical bone. It is also important to evaluate for possible edema and abscess of the middle and posterior cranial fossa and to diagnose as early as possible a partial or total thrombosis of the sigmo~'d sinus. The middle ear in mastoiditis is Seminars in Roentgenology, Vol XXXV, No 1 (January), 2000: pp 2-11
IMAGING OF MIDDLE EAR PATHOLOGY
usually filled up with granulation tissue that appears isodense on CT. This one shows only the aeration of the middle ear and the possible osteitis (Fig 1). A spin-echo (SE) T l - w e i g h t e d sequence in MRI is more useful to demonstrate the mucosa hyperplasia isointense to hyperintense on T l - w e i g h t e d scans because of hyperemia, bright in T1 after Gadolinium injection. If a keratoma is associated, its intermediate signal will contrast with the surrounding bright granulation tissue after contrast medium injection in T I . The main information provided by MRI is the possible extension of the infection to the meninges, temporal lobe, and cerebellum) An M R A must always complete the conventional M R study searching for a thrombosis of the sigmoid sinus even if there is no clinical evidence of this pathology.
Tympanosclerosis Tympanosclerosis is a kind of scar in chronic otitis media. It represents the result of years of inflammation. This pathology may nevertheless be associated with an acute onset of inflammation. Usually there is no need for imaging, but if an associated cholesteatoma is expected CT would be very useful for the diagnosis of the epidermic tissue among the calcified material. Tympanosclerosis is a hyalinization of the middle ear mucosa and appears as calcifications in the tympanic membrane, tendons, ligaments, ossicles, and mucosa of the middle ear. CT demonstrates the amount o f calcifications particularly in the stapes footplate, which is irregular, thickened, and hyper-
3
Fig 2. Tympanosclerosis. CT shows calcification of the footplate, which is thickened (arrow).
dense on high-resolution horizontal CT sections (Fig 2). A particular interesting condition is the ossification of the middle ear called osteomatous otitis, which may lead to surgical difficulties when discovered during a tympanic surgery. The middle ear is then more or less filled with bone that may be located in the attic, encroaching on the ossicles, associated or not with a cholesteatoma. CT demonstrates the amount of calcified material, the position and structure of the ossicles, the possible associated keratoma with or without a fistula of a semicircular canal (usually the lateral one).
Aggressive Hyperplasia This entity is not as well known by radiologists. It represents an invasion of the middle ear by granulation tissue, which appears at histological examination as villosities. This pathology may be as aggressive as a cholesteatoma without any presence of an epidermic tissue. A fistula of the cochlea or semicircular canals or erosion of the facial nerve canal with or without facial palsy are possible. CT shows the total filling of the middle ear and the possible defect of its inner wall (Fig 3). MRI demonstrates the absence of any cholesteatoma with an enhancement of the material within the tympanic cavity.
Cholesterol Granuloma
Fig 1. sinus.
Mastoiditis. CT shows thrombosis of the sigmo'id
Cholesterol granuloma is a result of a hemorrhage of the mucosa with a granulation tissue reaction. It may be very small or well developed in the middle ear. The signal is bright on T I and T2 spin-echo sequences. 2
4
VEILLON ET AL
ium injection may help arrive at a diagnosis, demonstrating an isointense mass surrounded by a crown of hyperintense tissue related to the peripheral hyperplasia. 7 It is always important to compare in chronic otitis media the results provided by MRI and by CT. The Postoperative Middle Ear in Chronic Otitis Media
Fig 3. Aggressive hyperplasia. CT shows erosion of the canal of the facial nerve (arrow). Tympanosclerosis of the internal attic encroaching on the malleus and incus (curved arrow).
Cholesteatoma The cholesteatoma represents a classic complication of chronic otitis media usually after a perforation in the upper and posterior part of the drum. The epiderm is then allowed to invade the attic. If the otologist is aware of the presence of a cholesteatoma, he does not know its extension and relationships with the facial nerve, the cortical of the inner ear, the tegmen, and the sigmoid sinus. There is a big difference between a pearl of cholesteatoma in the external attic and an cholesteatomatory mass invading the antrum and posterior cranial fossa. The first can be removed in less than l hour, but the second will require an operation of 6 or 7 hours. The clinical otoscopical appearance may be the same. The keratoma appears as a mass more or less round shaped in the attic. 3,4 It can spread in the middle ear with usually spherical margins (Fig 4). Sometimes most of the epidermoid tissue has been evacuated and persists only as a destruction of the walls without any CT content in the tympanic cavity. When the extension of the cholesteatoma is suspected to invade the middle or posterior cranial fossa, MRI will demonstrate the relationship of the mass to the dura mater. 5 The dura is usually not destroyed but compressed by the mass. Cholesteatomas appears isointense on Tl-weighted, slightly white on T2-weighted scans, with no contrast enhancement after Gadolinium 6 injection. Fat saturation may be helpful when injecting contrast medium. In some doubtful cases, MRI may be useful particularly when soft tissue fills up the totality of the tympanic cavity without significant bony destructions. MRI with and without Gadolin-
There are two kinds of surgical techniques approaching the middle ear: the first one preserves the external auditory canal; in the second one, the posterior wall of the tympanic bone is removed. There are different variants around these techniques. The first techniques (with the intact external canal wall) for many years has been done in two stages: the first stage consists of removing the keratoma, the second stage after 18 months checks for absence of an epidermic recurrence or rest of cholesteatoma within the tympanic cavity and allows an ossicular reconstruction among a dry ear. If after the first operation there is no clinical evidence of a recurrent cholesteatoma, and hearing has been improved during the first time, CT will be mandatory for deciding whether or not the second operation will be performed. Even if a second look is necessary, CT is useful for evaluating the extension of a possible recurrent cholesteatoma. In our experience we consider the shape of the soft-tissue content within the operated cavity. It is then possible to diagnose, in more than 85% of the
Fig 4. Secondary cholesteatoma. CT shows the mass is developing in the posterior part of the tympanic cavity.
IMAGING OF MIDDLE EAR PATHOLOGY
cases, the presence of a cholesteatoma compared with fibrosis or hyperplasia. CT must be performed in the axial, coronal, and sagittal planes. In scalloped masses with irregular margins, a cholesteatoma is likely. Bowl-shaped masses in the external attic are also related to cholesteatoma. 3 In thin concave limited soft-tissue masses, fibrosis is favored as the diagnosis. With well-defined straight soft-tissue content inflammation or fibrosis should be diagnosed. Tissue covering the periphery of the cavity is usually related to hyperplasia. In cases with doubtful images, MRI should be of some interest using the Tl-weighted scan with and without Gadolinium in an axial and sagittal plane after contrast medium injection. The keratoma appears as an intermediate signal without any contrast enhancement surrounded by enhanced granulation tissue (Fig 5). THE MALFORMATIONS
The malformations of the middle ear are often associated with congenital abnormalities of the external ear. Thus, the absence of the tympanic bone is usually associated with a fusion of the malleus and incus and sometimes a fixation of these ossicles to the lateral wall of the tympanic cavity. The fixation of an ossicle may be the only sign of a malformation. All the parts of the ossicles may be missing, particularly the long process of the incus. This diagnosis is quite easy to make particularly when performing oblique sections of the ossicles perpendicular to the footplate allowing one to
Fig 5. Recurrent cholesteatoma. MRI shows Tl-weighted sequence with Gadolinium injection. The intermediate signal of the cholesteatoma is visible surrounded by a rim of enhancement in the tympanic cavity (curved arrow). The cholesteatoma is also developing in the mastoi'd region (arrow).
5
delineate the missing part of the long process of the incus. The fixation of the stapes is more difficult to demonstrate. It is quite important to consider the increased thickness of the footplate associated with some ossicular or wall malformations. The shape of the stapes may be changed, 8 and the tendon of the stapedius may be missing or calcified. CT shows the absence of the stapedius canal close to third portion of the facial nerve canal. The absence of the stapes is easily demonstrated usually associated with a lowering of the tympanic part of the facial nerve (Fig 6). The change in the position of the facial nerve canal is one of the most important pieces of information provided by CT in middle ear malformations. This part of the nerve, 9 normally located above the oval window, should mn in the window itself. The facial nerve is then clearly visible close to the footplate. The little airspace located between the footplate and the facial nerve may disappear in cases of footplate anomalies. The third portion of the facial nerve canal is displaced anteriorly in all the tympanic bone aplasia. The round window is also an important opening to evaluate. It may be small or absent. Its presence must always be considered. Among the walls of the tympanic cavity, the most important to appreciate is the tegmen tympani, which may be lowered, the duramater is usually normal. TRAUMATIC LESIONS OF THE MIDDLE EAR
Fractures of the middle ear are very frequent (80% to 90%) in skull-base trauma. The traumatic wave runs in the middle ear entering the temporal bone through the squamous bone, the tympanic bone, or the posterior part of the petrous bone. The ossicles are then submitted to a force with a possible displacement or fracture. CT is the best examination to appreciate the displacement of the ossicles. ~ The most sensitive ossicle is the incus because of its poor attachments. Reformated CT sections in coronal and sagittal planes give nice views of the injured ossicles. A particular attention must be paid to the stapes: the crus may be broken with a clear conductive hearing loss. The footplate is rarely fractured. It is more often displaced in the vestibule, therefore CT and MRI are very important to analyze the position of the stapes in the inner ear. The perilabyrinthine leakage that occurs through the oval window (center or periphery) depends on the degree of stapes displacement. An air bubble
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VEILLON ET AL
Fig 6. Malformation. (A) Malformation of the stapes. CT shows a single crus is visible medially to the long process of the incus (arrow), (B) CT shows absence of the stapes (arrow).
may be demonstrated in the vestibule (Fig 7). Fractures of the round window and the disruption of the round window membrane must also be considered. It has been described in MRI the possibility of a contrast medium enhancement in the region of the round window associated with a fistula of the perilymph. The occipital fracture running in the inner ear usually respects the tympanic cavity (translabyrinthine fractures). They are quite rare (10% of the temporal bone traumatisms). In 5% of the cases, trauma may involve both middle and inner ears. In such cases, a particular attention must be paid to the windows that are often injured by the traumatic wave.
OTOSCLEROSIS Otosclerosis is the development of a spongious bony tissue in the labyrinthine bone particularly in
~
~ !~!~ii~!~
the region and vicinity of some cartilaginous nests close to the anterior part of the oval window (fissula antefenestram). The footplate may be invaded by otosclerotic tissue. Usually this disease does not extend beyond the middle layer of the labyrinthine bone, the anterior part of the oval window, and the footplate. In some rare cases the otosclerotic foci may develop in the internal attic or the mesotympanum encroaching on the malleus and the incus (Fig 8). In CT these foci are demonstrated as white or grey bony masses originating in the lateral part of the labyrinthine bone, developed in the medial attic. MRI is useful for analyzing the active or inactive part of the otosclerotic foci within the middle layer of the labyrinthine bone but does not give further information about the development of the lesion in the middle ear. In postoperative patients CT nicely demonstrates
~ ~ 84
Fig 7. Fracture of the temporal bone in the middle ear CT. The fracture is running in the posterior part of the tympanic cavity before reaching the anterior wall (arrows). Air bubble is shown in the vestibule (curved arrow),
Fig 8. Otosclerosis. CT shows development of an otoscierotic focus in the region of the round w i n d o w with protrusion in the tympanic cavity (arrow).
I M A G I N G O F M I D D L E EAR P A T H O L O G Y
Table 1. Middle Ear Pathology and CT Imaging Chronic Otitis Media Spiral
+++
Non spiral +, recommended;
Traumetisms
.
Malformations
+++ .
++++ .
Tumors +++
.
Otosclerosis
Postoperative Otosclerosis
-
+++
+++
+
-, not useful.
the position of the ossicular prothesis extremities: the medial one in the oval window and the lateral one close to the long process of the incus. A subluxation of the prosthesis in the vestibule may be demonstrated by CT. Particular attention must be paid if the distal part of the prosthesis reaches the center of the vestibule. The lateral extremity of the prosthesis may be taken down and separated from the lenticular process. Reformated sections allowed by the spiral CT technique are very nice for demonstrating malposition of the prosthesis. MRI may demonstrate the medial extremity of a dislocated prosthesis. It can also demonstrate a possible labyrinthine granuloma if a high-resolution T2weighted sequence is used. In some cases, the prosthesis is deficient due to incus long process destruction easily delineated by CT (Tables 1 and 2). TUMORS AND PSEUDOTUMORS OF THE MIDDLE EAR
Primitive Cholesteatoma This lesion is made of an epidermal remnant in the mesotympanum usually far from the attic. It may be very small or may be large, invading most of the middle ear. There is no history of chronic otitis media, the drum is normal or malformed. The main clinical sign is a conductive hearing loss with a possible mass detected at the otoscopic examination. J0 CT shows the mass in the mesotympanum without any sign of chronic otitis media (Fig 9). The long process of the incus or the stapes may be
destroyed. MRI is usually of small interest in this field because this lesion rarely invades the inner ear.
Glomustympanicum Tumor It originates in little vascular bodies localized along the Jacobson's nerve course close to the promontory. It may be very small: 1 to 2 mm or extend in the totality of the tympanic cavity. The lesion may extend into the Eustachian tube and the Jacobson's canal. The clinical signs are that of a blue drum with pulsatile tinnitus. CT demonstrates a mass close to the course of the tympanic nerve whose density is enhanced after contrast medium injection. If a serous fluid surrounds the mass the diagnostic may be more difficult. MRI is very useful. On T1 scans with Gadolinium, H the contrast-enhanced mass close to the promontory among the grey signal of the serous fluid is evident (Fig 10). In all the cases, an angiogram is proposed confirming the diagnosis and allowing possible embolization. Invasion of the middle ear is possible by a glomus jugulare tumour originating in the jugular adventice. The extension to the tympanic cavity represents only a part of the tumor centered on the jugular foramen with high signal on Tl-weighted scan after contrast medium injection. There may be small signal void structures corresponding to arterial vessels running into the lesion. The meningeal reaction is usually small.
Table 2. Middle Ear Pathology and MR Imaging Chronic Otitis Media (mastoiditis, aggressive otitis, giant secondary chole)
Traumatisms (facial nerve contusion)
+
++
+++
+ + (meningo-
-
+
+++
T2
+ (cholesterol
+++) -, not useful.
Angio MR
+
-
+ Ho
+++
+, r e c o m m e n d e d ;
Stapedial Artery
-
+ + Ho
T1 + G a d o
granuloma
Postoperative Middle Ear (chole)
Ho
T1
Ho
Malformation
Tumors (clinical context)
cele)
+
8
Fig 9. Primitive cholesteatoma. CT shows mass developing in the anterior part of the tympanic cavity close to the malleus (arrow),
The Adenoma In the setting of chronic otitis media the epithelium of the tympanic cavity may produce an adenoma encroaching on the ossicles. CT shows a mass in the middle ear (Fig 11) whose signal in MRI is intermediate in T 1, high after Gadolinium injection. The lesion is not really centered on the Jacobson's nerve canal; a malignant lesion as an adenocarcinoma may give the same presenta-
VEILLON ET AL
Fig 11. Adenoma of the middle ear. CT shows the mass in encroaching on the malleus (arrow).
CT demonstrates a mass in the course of the facial nerve invading the middle ear destroying or not the stapes or the incus. Neuroma of the third portion of the facial nerve m a y extend into the chorda tympani and the middle ear. MRI will show an intermediate signal the mass on Tl-weighted, scans, hyperintense on T2W scans and avidly enhancing involving the facial nerve canal. 13
tion.l,12,t3 Neuroma of the Facial Nerve
Neuroma of the Eighth Nerve
All the parts of the facial nerve may be involved by a neuroma. It may extend in the tympanic cavity through the geniculate ganglion, the tympanic, or mastoid portions. A facial palsy may be present or not. If it is absent, the only sign of the neuroma may be a conductive hearing loss, which could lead to the false diagnosis of an otosclerosis.
Schwannomas of the eighth nerve may extend into the labyrinthine lumen. It may also invade the middle ear through the lateral semicircular canal, the promontory, or the windows particularly the round one. A T l - w e i g h t e d sequence will show the contrast enhancement in the labyrinthine lumen
Fig 10. Glomus tumor of the tympanic cavity MRI (T1weighted sequence) with Gadolinium injection. Mass enhanced in the tympanic cavity (arrow) surrounded by a serous otitis media.
Fig 12. Neuroma of the internal auditory meatus, the labyrinth, extended to the middle ear. MRI shows T1-weighted sequence with Gadolinium injection, The neuroma is very well delineated running from the internal auditory meatus through the internal ear to the middle ear (arrow).
IMAGING OF MIDDLE EAR PATHOLOGY
9
and the tympanic cavity (Fig 12). The T2 highresolution sequence will diagnose a mass in the labyrinthine lumen.
Hemangioma Hemangiomas of the facial nerve are well known in the geniculate ganglion but are not as common in the chorda tympani.
Carcinoid Tumor of the Middle Ear This lesion is well known from the otologists and is responsible of a conductive hearing loss. It may be present with a little bulging of the drum, with or without perforation. 14 CT shows up a mass in the tympanic cavity, well marginated, with or without ossicular destruction, highly vascularized with avid Gadolinium enhancement in T 1 after contrast medium injection and a high signal in T2 (Fig 13). The diagnosis is made after the electronic microscopic examination demonstrating intracytoplasmic neuroendocrine granulations. The evolution is not very aggressive.
Fig 14. Meningioma of the posterior wall of the petrous bone extended to the middle ear through the Hyrtl fissure. MRI shows Tl-weighted sequence with Gadolinium injection. The white mass in the middle ear is well delineated (arrow).
to the tympanic cavity on Tl-weighted scan with Gadolinium injection (Fig 14).
Tuberculosis of the Middle Ear
A meningioma may be discovered in the tympanic cavity. It may originate in the cerebellopontine angle, the middle cranial fossa particularly in the meninges close to the geniculate ganglion. There are several ways for the meningioma to reach the tympanic cavity: the Hyrtl fissure, the Eustachian tube, and the tegmen tympani. The only sign of the lesion may be a serous otitis media leading to imaging when it occurs in elderly patients. ~5 CT discovers the sign of a meningioma in the posterior or middle cranial fossa. MRI will delineate the path
Tuberculosis is a rare entity in the tympanic cavity. It may be diagnosed clinically when it extends in the external auditory meatus with the presence of caseum directly analyzed by the otologist. CT shows a soft-tissue mass destroying the ossicles in the tympanic cavity with possible extension to the adjacent regions (middle and posterior cranial fossa). Some geodes may be delineated in the petrous bone; the lesions appear with an intermediate signal in T1, high in T2 with enhancement within the petrous bone and the meninges of the adjacent regions (Fig 15). 16
Fig 13. Carcinoid tumor of the attic. MRI shows T1weighted sequence with Gadolinium injection, An enhanced mass is visible in the lateral part of the attick (arrow),
Fig 15. Tuberculosis of the left petrous bone. MRI shows Tl-weighted sequence with Gadolinium injection,
The Meningioma of the Tympanic Cavity
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Fig 16. Histiocytosis. CT shows destruction of the posterior part of the petrous bone (arrow).
VEILLON ET AL
Fig 18. Acute leukemia of the middle ear. CT shows a soft-tissue mass is developing in the middle part of the tympanic cavity,
Histiocytosis X This granulomatosis is made of histiocytes and eosinophils. In the cytoplasm of the histiocytes, the electron microscopy discovers the presence of a rodshaped inclusion (Birbeck granule). It mainly occurs in children showing evidence of an external and middle ear inflammation, t7 One or several cavities may be discovered by CT particularly in the mastoid region (Fig 16) with, in MRI, an intermediate signal on T1, high on T2 and with a strong contrast enhancement after Gadolinium injection on T1. MRA may show thrombosis of the sigmo'id sinus.
Aneurysm of the Internal Carotid Artery This is a very rare entity often occurring in the postraumatic setting. The mass of the internal carotid petrous canal may obstruct the Eustachian tube or extend in the middle ear. MRA will suggest the correct diagnosis. Any surgical procedure with-
out knowing the presence of this pathology could lead to an injury of the internal carotid artery. THE MALIGNANT TUMORS OF THE MIDDLE EAR
Squamous Cell Carcinoma This lesion is well known in the auricle and the external auditory meatus. It is not so frequent in the tympanic cavity, usually complicating a chronic otitis media. Its development may be very limited or, on the contrary, very aggressive involving the middle cranial fossa, the mastoid, the facial nerve canal, the labyrinth, and the cerebello-pontine angle (Fig 17). There is no specific appearance in MRI: intermediate signal in TI, intermediate signal in T2. The main problem is to delineate the extension to the extension to the adjacent intracranial structures and the possible involvement of the facial nerve.
Fig 17. Squamous cell carcinoma. (A) Carcinoma of the posterior part of the petrous and squamous bone. CT shows destruction of the external cortical bone (arrow). (B) Same case MRI shows Tl-weighted sequence with Gadolinium injection, The mass developing in the middle ear is enhancing after contrast medium injection (arrow).
IMAGING OF MIDDLE EAR PATHOLOGY
11
The a d e n o c a r c i n o m a o f the m i d d l e ear has no specific features. M R I and C T will a p p r e c i a t e the e x t e n s i o n o f the lesion. 18
Acute Leukemia
Lymphoma L y m p h o m a is rare in the m i d d l e ear and usually e x t e n d s f r o m the external auditory m e a t u s w i t h o u t any specific sign in C T or M R I . L y m p h o m a m a y e x t e n d f r o m p a r o t i d g l a n d source.
This lesion is not so well k n o w n b y radiologists. It a p p e a r s as a soft tissue within the m i d d l e ear usually a s s o c i a t e d w i t h a p r e s e n c e o f y o u n g specific cells in the l a b y r i n t h i n e l u m e n w i t h o u t b o n y destruction. T h e signal is i n t e r m e d i a t e on T1, high on T2 w i t h o u t any G a d o l i n i u m e n h a n c e m e n t . It looks like i n f l a m m a t i o n , but this entity m u s t be c o n s i d e r e d b y the r a d i o l o g i s t w h e n k n o w i n g the c o n t e x t o f an acute l e u k e m i a (Fig 18).
Metastases M e t a s t a s e s m a y i n v o l v e the m i d d l e ear but in m o s t o f the cases, r e p r e s e n t s an e x t e n s i o n f r o m the b o n y structures o f the p e t r o u s bone. U s u a l l y prim a r y t u m o r s are f r o m the breast, prostate, or lung. M R I is very useful for the e v a l u a t i o n o f an e x t e n s i o n to a d j a c e n t regions.
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