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Imaging conductive hearing loss Poster No.: C-1556 Congress: ECR 2012 Type: Educational Exhibit Authors: R. Swamy , P. Khatri , S. Ghosh-Ray , R. K. Lingam ; Harrow/ 1 1 1 2 1 2 UK, HA13UJ/UK Keywords: CT-High Resolution, CT, Head and neck, Ear / Nose / Throat, Anatomy, History, Congenital DOI: 10.1594/ecr2012/C-1556 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. www.myESR.org Page 1 of 29 Learning objectives 1. To outline the essential CT anatomy of the conductive hearing pathway 2. To review the common causes of conductive hearing loss in adults and to illustrate their radiological features on high resolution CT of the temporal bones. 3. To highlight the important CT features which guide surgical management. 4. To note the limitations of CT in the imaging of conductive hearing loss. Background There are many causes of conductive hearing loss. High resolution CT, due to its excellent depiction of the anatomy of the conductive hearing pathway, can aid in the detection and management of the various causes. Sound passes down the external auditory canal (EAC) to the tympanic membrane. This energy is then amplified due to the relative size of the tympanic membrane to the oval window and lever action of the connecting ossicles. Fig. 1 on page 2 Conductive hearing loss (CHL) disrupts this normal passage of sound between the external ear and the cochlea. The clinical evaluation of CHL includes a history of hearing loss associated with ear discharge/fullness/pain, trauma, tinnitus and vertigo. The examination involves otoscopy, tuning fork tests and a complete head and neck examination (as needed). A Tympanogram is performed which measures mobility of tympanic membrane. Acoustic reflex can be performed to detect the presence of a stapedial reflex which can be diminished in otosclerosis. Pure Tone Audiogram (PTA): measures hearing thresholds via air and bone conduction. An air-bone gap suggests CHL. Fig. 2 on page 3 Images for this section: Page 2 of 29 Fig. 1: Image of the normal conductive hearing pathway. Sound travels through the external auditory canal, through the tympanic membrane via the middle ear ossicles into the inner ear. Page 3 of 29 Fig. 2: Figure 2: demonstrating the investigation of hearing loss with (a)normal tympanogram,(b)Ossicular discontinuity - hypermobile TM, (c)Normal Audiogram, (d)Audiogram showing an air-bone gap typical of otosclerosis (double arrow) Page 4 of 29 Imaging findings OR Procedure details There are many causes of conductive hearing loss. High resolution CT, due to its excellent depiction of the anatomy of the conductive hearing pathway, can aid in the diagnosis and management of the various causes. Conductive deafness, can be secondary to causes from the external auditory canal, the middle ear or bony labyrinth Table 1 on page 8 . Below is a brief description of the various causes and their appearances on high resolution CT of the temporal bones. External auditory canal(EAC): 1. Wax: Luminal low density material filling the EAC. No bony erosion or expansion of the EAC Fig. 3 on page 9 2. EAC atresia: Hearing loss caused by inefficient conduction of sound to the inner ear. Essentially, children with aural atresia have hearing loss because the sound cannot travel into the (usually) healthy inner ear-there is no ear canal, no eardrum, and the ossicles are underdeveloped. Fig. 4 on page 11 Fig. 5 on page 10. A CT is perfomed to evaluate the middle and inner ear structures 3. Keratosis obturans: Is caused by abnormal accumulation and obstruction of the bony external auditory canal from desquamated keratin without erosive bony changes. Imaging demonstrates homgenous soft tissue within EAC with bony expansion but no destruction. CT is performed to evaluate for any bony erosion or suspicious features. Fig. 6 on page 12 Treatment would need excision of keratin plug which may require anaethesia. 4. Otitis externa: Presents with otorrhoea and otalgia, usually occurs in elderly diabetic patients. On CT destructive, osteomyelitic appearance of the bony EAC affecting the inferior portion with spread of infection/ abscess formation in the parotid space/ mastoid/ TM joint. 5. EAC cholesteatoma: Erosive soft tissue mass +/- bony flecks in matrix with scalloping of margins. Fig. 17 on page 23 5. Medial canal fibrosis: Band of soft tissue filling the medial EAC, abutting the tympanic membrane. Surgical intervention corrects the hearing loss. Fig. 19 on page 25 Page 5 of 29 6. EAC osteoma: Rare benign focal, pedunculated bony overgrowth of osseous EAC with normal overlying soft tissues. Usually asymptomatic and an incidental finding. Clinically difficult to differentiate from EAC exostoses. Fig. 7 on page 14 Fig. 8 on page 13 7. Eac exostoses: Also called "surfers ear" is a benign overgrowth of the bony EAC, lesions are usually located medial to isthmus of EAC. Patients are usually young males with chronic history of prolonged cold water exposure( swimmers, surfers, divers). 8. Tumours: Occur in elderly patients., secondary involement from regional tumours is commoner than primary. CT demonstrates osseous destructive changes which is crucial as bony invasion predicts treatment outcome. The parotid nodes are 1st order drainage nodal group. 9. Bony dystrophies: Pagets disease, Fibrous dysplasia, osteopetrosis These are rare and cause hearing loss either by narrowing of the EAC or middle ear or involve the otic capsule.Fig. 16 on page 22 Wet middle ear: 1. Chronic serous otitis media: Commonest cause of CHL in children. Imaging shows non dependant opacification of the middle ear +/- mastoid with or without ossicular erosion. Improves with grommet insertion. Fig. 20 on page 26 2. Cholesteatoma: Accumulation of desquamated keratin epithelium in the middle ear cleft or any other pneumatized portion of the temporal bone. Imaging demonstrates non dependant soft tissue in the Prussack's space with scutum, ossicle or lateral epitympanic wall erosion. CT is performed to look for extent and complications of cholestatoma( labyrinthine fistula, tegmen erosion etc). Surgery is treatment of choice with follow up to look for recurrance. Fig. 10 on page 16 Dry middle ear: 1. Ossicular disclocation: (a) Traumatic: Longitudinal fractures are caused by tempro-parietal trauma, associated with high incidence conductive deafness secondary to ossicular disruption/injury. These fractures typically spare the otic capsule and sensorineural hearing loss is unsual Page 6 of 29 In contrast, transverse fractures are secondary to fronto occipital trauma, often involve the inner ear and cause sensorineural hearing loss. A conductive hearing loss can present at a later stage due to ossicular disruption. Imaging: Best identified on axial high resolution CT images. CT or MR angiogram may be performed if surrounding structues are involved. Ice cream(head of the Malleus) off the cone( incus) Fig. 14 on page 20 (b) Post surgical: Ossicular disruption may be a consequence of middle ear surgery or dislodgement of an ossicular prosthesis. Fig. 11 on page 17 2. Tympanosclerosis/ myringosclerosis: Calcific, bony or fibrous middle ear foci form secondary to chronic otitis media. Involvement of the tympanic membrane only is referred to as myringosclerosis. Fig. 9 on page 15. CT is useful to exclude a cholesteatoma and ossicular disruption. 3. Otosclerosis: Presents as uni/bi lateral hearing loss(conductive or mixed) in a young patient. Absent stapedial reflex and Carhart's notch ( air-bone gap on audiogram)is not always seen. Can be of fenestral or cochlear types.Fig. 13 on page 19 On CT Fenestral otosclerosis(FOto) is seen as a radiolucent focusat the anterior margin of oval window in the early phase. Late phase shows heaped up new bone formation around oval and round windows. Cochlear otosclerosis(COto) is seen as focal lytic plaques in pericochlear labyrinth. Checklist: "If COto is present, FOto is also present- must always look at anterior margin of oval window for FOto" Check involevement of round window- narrowing of it makes cochlear implantation difficult. Rare causes 4. Semicircular canal dehiscence(SSCD) : Rare cause of conductive hearing loss with few reported cases. SSCD introduces a 'third' window into the inner ear which produces the airbone gap by (1) shunting air-conducted sound away from the cochlea, thus elevating air conduction Page 7 of 29 thresholds, and (2) increasing the difference in impedance between the scala tympani 2 and scala vestibuli, thus improving thresholds for bone-conducted sound . Fig. 12 on page 18 5. Oval window atresia: Ossific membrane seen overlying the oval window with superior migration of the facial nerve recess where the oval window should be. Fig. 15 on page 21 Overall CT is extremely good at demonstrating most causes of conductive hearing loss, however not all patients with conductive hearing loss require a CT: 1. 2. 3. 4. If an abnormality is confidently diagnosed clinically, is non-cancerous and is of known anatomical extent - CT does not aid clinical management. However where there is diagnostic uncertainty, and to stage cancerous lesions or define anatomical extent of non-cancerous lesions, such as infections or benign tumours - CT is a valuable investigation. CT imaging is also helpful in planning surgical approaches to best target lesions, allows identification anatomical abnormalities/variations as well as disease complications (such as vestibular fistulae and tegmen defects). Being able to show patients their disease and its proximity to vital structures is also valuable during the consenting process for a surgical procedure. The limitations of CT should also be recognised, it does not necessarily pick up all causes of a conductive hearing loss( for eg- only 70% of otosclerosis 3 is confidently diagnosed on CT ) and is at the cost of radiation to the patient Images for this section: Page 8 of 29 Table 1: Table summarising the known causes of conductive hearing loss. Page 9 of 29 Fig. 3: Luminal soft tissue filling the external auditory canal(arrow) is seen on the left in keeping with wax. Page 10 of 29 Fig. 5: Congenital atresia of the left external auditory canal: there is complete atresia of the inner two thirds of the external auditory canal( straight arrow). The pinna is visualised but not well formed(curved arrow). CT was performed for reconstruction surgery Page 11 of 29 Fig. 4: Congenital left external auditory canal( EAC)atresia (arrow), normal EAC is seen on the right side Page 12 of 29 Fig. 6: Keratosis obturans: Middle aged male presented with 2-month history of right hearing loss and auditory canal polyp protruding from the ear. On coronal high resolution CT of the temporal bones, extensive soft tissue (block arrow) is seen in the external auditor canal (EAC) with complete opacification of its inner 2/3rds abutting the tympanic membrane (star). The EAC is expanded with scalloping of the bony margins(curved arrow). Page 13 of 29 Fig. 8: EAC osteoma: Another patient, large bony outgrowth right EAC, on close inspection it is seen attached to the anterior wall of the EAC by a peduncle ( curved arrow) Page 14 of 29 Fig. 7: Right EAC osteoma: bony outgrowth in EAC, peduncle is again seen( curved arrow) Page 15 of 29 Fig. 9: Myringosclerosis: Middle aged woman presented with bilateral chronic serous otitis media. On clinical examination the right tympanic membrane had a central perforation with inferior white keratin and possible new bone formation within the hypotympanum. High resolution CT of the temporal bones revealed extensive calcification of the tympanic membrane on the right(arrow)in keeping with myringosclerosis. In addition on the right, there are abnormal ectopic calcifications within the middle ear cavity around the ossicles (starred)in keeping with tympanosclerosis Page 16 of 29 Fig. 10: Congenital cholesteatoma: Coronal High resolution CT shows middle ear soft tissue with ossicular destruction:figures a and b( arrows), and soft tissue in mastoid with erosion of bony septae : figure c( arrow) Page 17 of 29 Fig. 11: Patient with bilateral ossicular prostheses presented with right sided conductive hearing loss. MIP images from high resolution CT of the temporal bones revealed an incudo-stapedial( prosthetic) dislocation( block arrow). Normal alignment of the osscicular prosthesis is shown on the left( curved arrow). Appearance of a normal in-situ stapedial prosthesis is shown ( inset picture, double arrow) Page 18 of 29 Fig. 12: High -resolution Coronal CT of the temporal bones demonstrates bilateral superior semicircular canal dehiscence( arrows), reformatted sagittal- oblique CT image through the left semicircular canal shows full size of the dehiscence Page 19 of 29 Fig. 13: Bilateral fenestral and retrofenestral otosclerosis: Patient presented with rightsided conductive hearing loss with a history of left-sided surgery: On the high resolution CT of the temporal bones, focal bony lucencies are seen bilaterally at the fissula antefenestram(curved arrows) in keeping with fenestral otosclerosis. In addition, in the same patient, bony lucencies(arrows) are also seen bilaterally around the cochlea in keeping with cochlear (retrofenestral) otosclerosis Page 20 of 29 Fig. 14: Right temporal bone fracture with disclocation of the Incudo-malleal joint: icecream off cone(curved arrow). Normal incudomalleal( cone and cream of the ice cream cone respectively)joint is shown separately on the right( double arrow) Page 21 of 29 Fig. 15: Patient with left sided congenital hearing loss.CT demonstrates ossification of the oval window( block arrow) with posterior migration of the stapes(double arrow). Normal oval window is shown on the left( curved arrow) Page 22 of 29 Fig. 16: Patient with known fibrous dysplasia in long bones present with conductive hearing loss: High resolution CT of the temporal bones demostrated demineralised/ fibrous appearing ossicles( arrows)thought to be secondary to fibrous dysplasia. Normally mineralised ossicles are shown on the right(double arrow). Page 23 of 29 Fig. 17: EAC Cholesteatoma: Large soft tissue seen in the left EAC (arrow) with erosion of the posterior wall of EAC( chevron), this extends into the mastoid with bony destruction. Differential diagnosis would include Squamous cell cancer and malignant otitis externa Page 24 of 29 Fig. 18: Agressive soft tissue mass in the post surgical (canal wall down mastoidectomy) right EAC . Biopsy confirmed inflammatory tissue only in keeping with otitis externa. Page 25 of 29 Fig. 19: Medial canal fibrosis: Note the presence of concentric soft tissue in the medial aspect of the left EAC with opacification along the tympanic membrane( arrow) Page 26 of 29 Fig. 20: Child with bilateral chronic serous otitis media. Note the opacification of both middle ears with no ossicular destruction( arrows) Page 27 of 29 Conclusion CT can aid in the diagnosis of a variety of causes of conductive hearing loss. CT also provides other information which is important in the management of the various causes, in particular the multiplanar advantage of CT with axial and coronal imaging is a valuable tool as a roadmap for surgical planning . Personal Information Subspeciality Head and Neck Rdaiology SpR at North-West London hospitals NHS trust. ESOR Head and neck radiology subspeciality fellowship training centre. London References 1. Diagnostic Imaging: Head and Neck; Ric Harnsberger, Patricia Hudgins, Richard Wiggins, Christian Davidson 2. Superior semicircular canal dehiscence mimicking otosclerotic hearing loss.Merchant SN, Rosowski JJ, McKenna MJ. 3. Computed tomography and otosclerosis: a practical method to correlate the sites affected to hearing loss. Wycherly BJ, Berkowitz F, Noone AM, Kim HJ. Ann Otol Rhinol Laryngol. 2010 Dec;119(12):789-94. 4. Labyrinthine fistulae: pathobiology and management. Minor LB.Curr Opin Otolaryngol Head Neck Surg. 2003 Oct;11(5):340-6. 5. The role of computed tomography scanning in chronic otitis media.Tatlipinar A, Tuncel A, O#redik EA, Gökçeer T, Uslu C. Page 28 of 29 Eur Arch Otorhinolaryngol. 2012 Jan;269(1):33-8. Epub 2011 Mar 24. 6. Temporal bone trauma and the role of multidetector ct in the emergency department;Radiographics. 2011 Oct;31(6):1741-55. Zayas JO, Feliciano YZ, Hadley CR, Gomez AA, Vidal JA. Page 29 of 29