Middle ear CT imaging: Review of anatomy and common pathology

Transcription

1 Middle ear CT imaging: Review of anatomy and common pathology Poster No.: C-0665 Congress: ECR 2017 Type: Educational Exhibit Authors: M. R. Campos Arenas, M. C. Sánchez-Porro, J. Garrido Rull ; CADIZ/ES, Cádiz/ES, 11010/ES Keywords: Ear / Nose / Throat, CT, Diagnostic procedure, Inflammation, Congenital, Trauma DOI: /ecr2017/C-0665 Any information contained in this pdf file is automatically generated from digital material submitted to EPOS by third parties in the form of scientific presentations. References to any names, marks, products, or services of third parties or hypertext links to thirdparty sites or information are provided solely as a convenience to you and do not in any way constitute or imply ECR's endorsement, sponsorship or recommendation of the third party, information, product or service. ECR is not responsible for the content of these pages and does not make any representations regarding the content or accuracy of material in this file. As per copyright regulations, any unauthorised use of the material or parts thereof as well as commercial reproduction or multiple distribution by any traditional or electronically based reproduction/publication method ist strictly prohibited. You agree to defend, indemnify, and hold ECR harmless from and against any and all claims, damages, costs, and expenses, including attorneys' fees, arising from or related to your use of these pages. Please note: Links to movies, ppt slideshows and any other multimedia files are not available in the pdf version of presentations. Page 1 of 21

2 Learning objectives The purpose of our educational exhibit is to: Provide an overview of anatomical structures of the temporal bone and the appearance of the middle ear in computed tomography imaging. Describe a systematic approach for the radiologist to explore the main functional components of auditory pathways when a CT is performed so that he can detect and evaluate the presence of congenital malformations, inflammatory conditions, trauma consequences or post-surgical changes. Background The middle ear is an air-filled cavity housed within the petrous portion of the temporal bone that contains the ossicular chain and is bounded by the tympanic membrane laterally, the inner ear structures medially, the tegmen tympani superiorly, and the jugular wall (floor) inferiorly. It communicates anteriorly with the epipharynx via the Eustachian tube. The tympanic cavity can be divided into three levels: Epitympanum (level above the tympanic membrane). It communicates with the mastoid via the aditus ad antrum. Mesotympanum: at the level of tympanic membrane. It contains the majority of the ossicular chain. Hypotympanum (level below the tympanic membrane). It contains the opening to the eustachian tube. The ossicular chain is composed of three bones: Malleus (head, neck, anterior process, lateral process, and manubrium). Incus (body, short process, long process, and lenticular process). Stapes (head/capitellum, anterior crus, posterior crus, and footplate). The manubrium of the malleus is attached to the tympanic membrane, which has a thickness of 0.1 mm and a diameter of about 10 mm. The head of the malleus articulates with the body of the incus in the epitympanum forming the incudomalleal joint, which has a characteristic "ice cream cone" configuration on axial sections (Image 1) Page 2 of 21

3 The lenticular process of the incus extends perpendicular to the long process of the incus and articulates with the head of the stapes, forming the incudostapedial joint. The footplate of the stapes attaches to the oval window of the vestibule. In Image 2 are shown some structures that radiologists need to pay attention to while performing a CT study: - Scutum: it is a sharp bony projection to which the tympanic membrane is attached superiorly. - Tegmen: it is a thin plate of bone that separates the dura of the middle cranial fossa from the middle ear and the mastoid cavity (tegmen tympani and tegmen mastoideum). - Posterior wall of the middle ear cavity: it includes, from lateral to medial, the facial recess, pyramidal eminence, sinus tympani, and round window niche (image 1). - Prussak space (superior recess): it is limited by the pars flaccida and scutum laterally and the neck of the malleus medially. Images for this section: Page 3 of 21

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5 Fig. 1 Fig. 2 Page 5 of 21

6 Findings and procedure details PATHOLOGY 1. CONGENITAL ANOMALIES OF THE MIDDLE EAR There is a great variety of malformed parts in the middle ear and they can be unilateral or bilateral. - Minor anomalies (only involvement of the middle ear): changes in configuration or size of the tympanic cavity, reduction of the distance between structures, fixated ossicles... - Major anomalies (associated with an involvement of the tympanic membrane and external ear): there may be aplasia, hypoplasia, thickening or thinning of ossicles. It may also exist fusion or excessive separation of joints inside the ossicular chain (Images 3-4) - Other anomalies: dehiscence of the facial nerve, apneumatized mastoid and aberrant courses of arteries and veins. Recommendations for the radiology report Existence (or not) of tympanic bone (external auditory canal). Presence (or not) of tympanic membrane. Mandibular condyle's position. Form and size of the tympanic cavity. Analysis of the ossicular chain and its anomalies. Presence of round window and oval window in a correct position. Facial nerve trajectory (useful for preoperative studies). Carotid artery and yugular vein's location. 2. INFLAMMATORY LESIONS 2.a) ACUTE OTITIS MEDIA It is primarily a disease of infants and young children. Patients present with fever, otalgia, and a red bulging tympanic membrane. The infection is usually caused by bacteria such and imaging is usually not necessary in uncomplicated acute otitis media. 2.b) ACUTE MASTOIDITIS Page 6 of 21

7 In a clinical situation that courses with postauricular erythema and edema, imaging is crucial to exclude complications, such as: Coalescent mastoiditis: Destruction of the mastoid trabeculae, with the possible development of a subperiosteal abscess. Petrous apicitis (image 5): It occurs in the setting of a pneumatized petrous apex (present in 30% of the population). It is characterized by septal and cortical destruction, osteitis, meningeal inflammation. Osteomyelitis. Intracranial complications: dural venous sinus thrombosis, epidural abscess, subdural empyema, meningitis, brain abscess... 2.c) CHRONIC OTITIS MEDIA (image 6) It may be due to underlying eustachian tube dysfunction or tympanic membrane perforation. Some of the important sequelae of chronic otitis media may have very similar appearances on CT images: Granulation tissue it does not destroy or displace the structures. Cholesterol granuloma: Common locations include the middle ear and the petrous apex. Cholesteatoma. 2.d) CHOLESTEATOMA (Images ) It is characterized by accumulation of desquamated keratin epithelium in the middle ear cavity or in other pneumatized portions of the temporal bone. Most cholesteatomas are acquired (98%; 80% associated with the pars flaccid and 20% associated with pars tensa), approximately 2% are congenital (child with no previous history of otorrhea, tympanic membrane perforation or otologic procedures). CT is the imaging mainstay of temporal bone inflammation. a) Acquired pars flaccida cholesteatoma: Expansile lobulated lesion in the Prussak space eroding the scutum, with medial displacement and erosion of the ossicles. b) Aquired pars tensa cholesteatoma: It is usually medial to the ossicles and displace them laterally. c) Congenital cholesteatoma: It is commonly located just above the opening of the eustachian tube. Complications of Cholesteatoma Page 7 of 21

8 EROSION OF... POSSIBLE RESULT Tegmen tympani (roof) Formation of a meningoencephalocele Bony facial canal (tympanic or mastoid portion) Facial palsy Semicircular canal Labyrinthine or perilymphatic fistula If only one cholesteatoma cell is missed and is not removed, the cholesteatoma may reoccur (residual cholesteatoma). The primary goal of surgery is eradication of disease and prevention of recurrence. Preservation or reconstruction of hearing is an important but secondary consideration. 2.e) TYMPANOSCLEROSIS A chronically scarring process which can lead to conductive hearing loss due to sclerotic fixation of the ossicles. It should be distinguished from otosclerosis that is a noninflammatory process characterized by demineralization in the region of the fissula ante fenestram at CT and, in the late phase, there may be sclerotic thickening around the oval window, at the stapes footplate and around the cochlear capsule. 3. TRAUMA CT is the modality of choice for evaluating temporal bone trauma, particularly fractures. Traditional system for classifying temporal bone fractures: - Longitudinal fracture (80%-90%): parallel to the long axis of the petrous portion of the temporal bone. It results in ossicular and tympanic membrane injury. - Transverse fracture (10%-20%): perpendicular to the petrous pyramid. It is associated with a higher risk of facial nerve injury. There is a newer system that shows better correlation with clinical outcome and complications: - The otic capsule-sparing fracture is much more common (94%-97%), results from a temporoparietal blow, and has an increased incidence of conductive hearing loss due to ossicular injury. Page 8 of 21

9 - The otic capsule--violating fracture (3%-6%) results from an occipital blow and has a higher incidence of facial nerve paralysis (30%-50%), sensorineural hearing loss and CSF fistula. It may be more important to describe the vital structures involved (ossicles, otic capsule, facial nerve, tegmen, external auditory canal, internal auditory canal, carotid canal) rather than classifying the fracture in a type or another. Complications of Temporal Bone Trauma Conductive hearing loss is caused by the disruption of the conductive chain, which may be due to ossicular luxation (more common) or fracture. Sensorineural hearing deafness could be caused by intracranial lesions or middle/inner ear pathology. CT can detect pneumolabyrinth and signs of perilymphatic fistulae but it can't detect subtle lesions within the inner ear. CSF Leak: CT depicts a bone defect in 70-93% of cases with clinically active leaks, depending on series. Facial Nerve Injury: On CT we should search for a fracture line coursing through the facial nerve. Labyrinthitis Ossificans: the fluid-filled lumen of the otic capsule is replaced by bone (or fibrous tissue if in the early stages). On CT images, osseous attenuation is noted within the inner ear. Vascular Injury (arterial injury or venous sinus thrombosis). 4. IMAGING OF POSTOPERATIVE TEMPORAL BONE (images ) It is important to be familiar with some of the more commonly performed procedures and their corresponding imaging findings. 4.a) Myringotomy and Tympanostomy Tube Tympanostomy tubes are commonly inserted into the tympanic membrane via an incision in the tympanic membrane (myringotomy) for treating chronic or recurrent otitis media recalcitrant to medical management. The tubes usually fall out on their own after a few months, but medial migration occasionally occurs and can result in conductive hearing loss. 4.b) Mastoidectomy The different types of mastoidectomy essentially consist of resecting variable portions of the mastoid air cells and adjacent structures, which may be performed for treatment of Page 9 of 21

10 mastoiditis, cholesteatoma resection, cochlear implantation, or endolymphatic surgery, among other indications. - Canal-wall-up mastoidectomy: exenteration of the mastoid air cells. - Canal-wall-down mastoidectomy: in addition the posterior wall of the external auditory canal is resected. - A radical mastoidectomy includes removal of the tympanic membrane, malleus, and incus, with attempted preservation of the stapes. - Tympanomastoidectomy: mastoidectomy performed in conjunction with a middle ear procedure. The mastoid bowl remains clear and the presence of soft-tissue attenuation material on CT images may represent soft tissue grafts, granulation tissue or, in the appropriate scenario, recurrent cholesteatoma. On CT images, recurrent cholesteatoma is suspected when there is new bone erosion associated with a soft-tissue focus. 4.c) Ossicular Reconstruction - Stapes prostheses are used in patients with conductive hearing loss due to otosclerosis or congenital anomalies. - A partial ossicular replacement prosthesis substitutes the malleus and incus, and thus extends from the tympanic membrane to the head of the stapes. - A total ossicular replacement prosthesis extends from the tympanic membrane to the stapes footplate or oval window and is utilized if the stapes is also diseased. Ossicular prostheses can be composed of various materials including hydroxyapatite, metal, and plastic. Ossicular prosthesis failure most commonly results from migration or dislocation (it can also result from prosthesis fracture, recurrent cholesteatoma, pressure erosion of the ossicles, and perilymphatic fistula). 4.d) Cochlear Implantation Temporal bone CT imaging is useful for preoperative planning and avoiding complications and failure of cochlear implantation. Images for this section: Page 10 of 21

11 Fig. 3: Image 3: Axial CT image. Hypoplasia of left middle ear: decrease in the size of the tympanic cavity and ossicles malformations, associated with malformed external auditory canal and ear deformity. Page 11 of 21

12 Fig. 4: Image 4: Aplasia of middle and external left ear. There is an absence of tympanic cavity, the ossicular chain and the tympanic bone (not included). Page 12 of 21

13 Fig. 5: CT axial and coronal images. ACUTE MASTOIDITIS AND PETROSITIS. Occupation of mastoid cells, antrum and tympanic cavity with extensive bone erosion that affects the antero-medial wall of petrous apex of the temporal bone, communicating Page 13 of 21

14 with esphenoidal sinus. Laterally there is a communication between the mastoid cells and the external auditory canal and glenoid cavity of the temporomandibular joint. Note the integrity of the ossicular chain. Fig. 6: CT coronal image. SIMPLE CHRONIC OTITIS MEDIA. Hypotympanum's occupation without associating bone erosion. Page 14 of 21

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16 Fig. 7: CT axial and coronal images. CHOLESTEATOMA. The tympanic cavity is occupied by soft-tissue attenuation material that associates bone sclerosis, erosion of the ossicles and lost of the scutum's typical shaped-apperance. Fig. 8: CT coronal and axial images. PARS FLACCIDA CHOLESTEATOMA. Epitympanum's occupation caused by a lobulated soft-tissue mass that extends from Prussak space to the mastoid cells through the aditus ad antrum. There is bone erosion (the typical image of "ice-cream cone" has disapperad on axial image) and tympanic membrane retraction. Page 16 of 21

17 Fig. 9: CT coronal and axial image. 12-year-olded girl with history of acute otitis media and fever. Occupation of epitympanun, mastoid antrum and tympanic cavity by soft-tissue material. There is also bone erosion that affects the scutum and the ossicular chain, but also mastoid cells and mastoid walls. Histologically it corresponded to an inflammatory polyp. Page 17 of 21

18 Fig. 10: CT axial image. LABERYNTHINE FISTULA. There is a disruption of the anterior wall of the semicircular canal that communicates with the mastoid antrum. Page 18 of 21

19 Fig. 11: CT axial image. Surgical changes after radical mastoidectomy (mastoid cells and ossicular chain). The mastoid bowl remains clear and without soft-tissue attenuation material. Page 19 of 21

20 Fig. 12: CT coronal image. 69-year-olded male who underwent a radical mastoidectomy due to a cholesteatoma and cavity-filling with ceramic bone graft. Fig. 13: TYPES OF PROSTHESES Luers, J. C. and Hüttenbrink, K.-B. (2016), Surgical anatomy and pathology of the middle ear. J. Anat., 228: doi: /joa Page 20 of 21

21 Conclusion In this review we have demonstrated the repercussion of an adequate knowledge of the middle ear anatomy and its most common alterations that are detectable by CT: CONGENITAL MALFORMATIONS: Despite its low incidence, an early diagnosis is therefore essential. MIDDLE EAR INFECTIONS: Acute otitis media and its complications (acute mastoiditis, lateral sinus thrombosis ) or chronic otitis media. Detection of cholesteatoma plays such an important role given the aggressive surgical treatment that it requires in order to avoid local recurrence or recidivous cholesteatoma. TRAUMA: Conductive hearing loss is caused by the disruption of the conductive chain, which may be due to ossicular luxation or fracture. POST-SURGICAL CHANGES: Mastoidectomy, ossiculoplasty assessment, type of prosthesis, signs of disease progression or recurrence... It is important to get to know in detail the middle ear anatomy to recognize pathologic features through different imaging modalities. CT remains gold standard in the evaluation of ossicular chain and temporal bone, remaining crucial the detection of abnormalities by the radiologist. Personal information References Juliano A, Ginat D. Imaging Review of the Temporal Bone: Part I. Anatomy and Inflammatory and Neoplastic Processes. Radiology. 2013; 269 (1): Juliano A, Ginat D. Imaging Review of the Temporal Bone: Part II. Traumatic, postoperative and noninflammatory nonneoplastic conditions. Radiology. 2015; 276: Luers, J. C, Hüttenbrink, K.-B. Surgical anatomy and pathology of the middle ear. J. Anat. 2016; 228: Page 21 of 21