Imaging of Conductive Hearing Loss With a Normal Tympanic Membrane

Transcription

1 Neuroradiology/Head and Neck Imaging linical Perspective urtin onductive Hearing Loss With a Normal Tympanic Membrane Neuroradiology/Head and Neck Imaging linical Perspective Hugh D. urtin 1 urtin HD FOUS ON: Keywords: conductive hearing, ear, hearing loss, tympanic membrane DOI: /JR Received May 30, 2015; accepted after revision ugust 21, Department of Radiology, Massachusetts Eye and Ear, Harvard Medical School, 243 harles St, oston, M ddress correspondence to H. D. urtin (hugh_curtin@meei.harvard.edu). JR 2016; 206: X/16/ merican Roentgen Ray Society Imaging of onductive Hearing Loss With a Normal Tympanic Membrane OJETIVE. This article presents an approach to imaging conductive hearing loss in patients with normal tympanic membranes and discusses entities that should be checked as the radiologist evaluates this potentially complicated issue. ONLUSION. onductive hearing loss in a patient with a normal tympanic membrane is a complicated condition that requires a careful imaging approach. Imaging should focus on otosclerosis, and possible mimics and potential surgical considerations should be evaluated. The radiologist should examine the ossicular chain and the round window and keep in mind that a defect in the superior semicircular canal can disturb the hydraulic integrity of the labyrinth. onductive hearing loss happens when the full amplitude of an arriving sound wave does not reach the hair cells of the cochlea. nything interfering with the transmission of vibratory sound energy along the external canal across the middle ear into the labyrinth will give a conductive loss. Interference with the normal propagation of the full energy through the cochlea to the hair cells will also result in a conductive loss. Recently, interest has increased in various entities that allow decompression of sound within a normally hydraulically isolated labyrinth, an effect referred to as the third window phenomenon. T is typically the first imaging modality used to assess a patient with conductive hearing loss. linical history and otoscopic observations direct the radiologist toward different strategies for analyzing images. Evaluation of patients with otitis media or cholesteatoma emphasizes one set of landmarks, looking for bone erosion and extension of disease into areas difficult to see at surgery. red mass behind the tympanic membrane directs toward examination of the carotid and jugular plates to make the diagnosis. This article describes this institution s approach to evaluation of a patient with a conductive hearing loss, a normal tympanic membrane, and no obvious abnormality seen through the tympanic membrane at otoscopy. The primary focus is on otosclerosis and its clinical mimics, with a list of checkpoints for radiologists to examine when evaluating a patient with this complex condition set out in ppendix 1. Imaging Technique t this institution, we use either MDT (0.5- to mm collimation) or conebeam T (3D ccuitomo, J. Morita MFG) with an original slice thickness of mm. Images are reformatted to mm thickness for interpretation. MRI does not play a primary role. oth T technologies generate a 3D volume of data that can be reformatted into any plane. Technologists create standard planes based on the lateral semicircular canal [1] (Fig. 1). This canal is easily identified in the sagittal plane. The technologist generates the standard axial plane using a technique we refer to as connecting the dots of the anterior and posterior limbs. The standard coronal plane is perpendicular to the standard axial plane or perpendicular to the plane of the lateral canal. Use of standardized planes greatly simplifies analysis of this complex anatomy. ny oblique plane can be produced. The sharpest definition of a thin plate of bone is in the plane perpendicular to that structure. Many important structures are oriented in planes not optimally seen in the axial or coronal planes. Two commonly used planes are parallel and perpendicular to a line passing along the axis of the petrous apex [1, 2] (Fig. 2). These planes are approximated using the JR:206, January

2 urtin superior semicircular canal as a guide. onnecting the dots of the anterior and posterior limbs of the superior canal in the axial plane gives a plane perpendicular to the axis of the petrous bone. Referred to as the Pöschl plane or axial pyramidal plane, this plane shows the superior canal as a complete ring [2]. This plane is perpendicular to the facial nerve canal, the septations of the cochlea, and the bony margins of the vestibular aqueduct. The Stenvers plane passes along the axis of the petrous bone, is perpendicular to the Pöschl plane, and shows the superior canal in cross section. Otosclerosis The approach to evaluation of a patient with a conductive hearing loss and normal tympanic membrane begins with an examination of the oval window for otosclerosis. Otosclerosis presents with slowly progressing conductive hearing loss that usually starts in the second or third decade of life. Somewhat more common in female patients, otosclerosis is bilateral in approximately 80% of cases. The disease affects the otic capsule. bnormal bone is first identified just anterior to the oval window (Fig. 3). This bone can encroach on the stapes and grow onto the footplate, limiting the motion of the stapes and diminishing the transmission of sound from the ossicles to the inner ear. The dense bone of the otic capsule is replaced by a more vascular new bone [3]. This less mineralized bone has a lower density than the normal otic capsule and, on T, appears gray when compared with the whiter normal bone [4 7]. ecause of the lower density bone, the disease is also called otospongiosis. later presumably less active phase can occur where the bone becomes more dense and sclerotic. The bone still appears to encroach on the footplate but has a density closer to that of the otic capsule and thus may be difficult to identify. The lower density bone can be appreciated in the axial or the coronal plane. lthough almost always forming initially at the anterior margin of the oval window, abnormal bone can often follow along other margins as well. lesion involving the oval window is referred to as fenestral. Involvement of the otic capsule separable from the oval window is referred to as retrofenestral otosclerosis or cochlear otosclerosis and can give a sensorineural component to the hearing loss. In almost every case, fenestral otosclerosis is also present. primary fenestral lesion of otosclerosis fixes the stapes. Treatment involves making an opening in the footplate and inserting a stapes prosthesis (Fig. 4). This procedure reestablishes the connection between the ossicles and the perilymphatic channels of the labyrinth. t this institution, the most common prosthesis is a thin wire attached by a small hooked wire to the long process of the incus and a small piston entering the hole in the stapes, but many variations are available. Surgical success depends on precise prosthesis positioning, but other abnormities can limit the effectiveness of the surgery or can mimic otosclerosis, leading to an incorrect diagnosis. These abnormalities are discussed next. Round Window Occlusion Round window occlusion can cause conductive hearing loss by adding resistance to the propagation of the sound energy along the cochlea [8 10]. The round window membrane normally moves in synchrony with the footplate of the stapes. Occlusion of the round window increases the resistance to acoustic energy entering the cochlea. No decompression of the sound energy occurs in patients with round window occlusion, so more energy is needed to displace the basilar membrane and conductive hearing loss results. Round window occlusion can occur with inflammatory tissue, bone lesions, and even a high riding jugular bulb. The window can be congenitally absent [11, 12]. ny of these abnormalities can cause conductive hearing loss. Indeed, otosclerosis can involve the round window and, rarely, completely occlude the niche (Fig. 5). Such occlusion can limit the effectiveness of a stapes prosthesis [13]. The prosthesis can transmit energy to the inner ear, but the increased cochlear input impedance resulting from a completely closed round window dampens acoustic energy propagation, thus limiting the effectiveness of the prosthesis. s long as a small part of the round window is open, it may function relatively normally. The radiologist should determine whether the round window is completely occluded or there is at least a small open area against the membrane (Fig. 5). Superior Semicircular anal Dehiscence and the Third Window Phenomenon bony defect in the superior semicircular canal can decompress the energy of the sound wave (Fig. 6). Normally, the labyrinth is a closed hydraulic system. ecause a liquid cannot be compressed, when the footplate is displaced inward, all of the energy is transmitted through the cochlea to the round window membrane. If the superior canal contains a defect, the canal is no longer hydraulically inert. Some sound energy will be redirected along the canal to this third window and therefore will not be available to the cochlea. The amplitude of the sound wave drops, resulting in a conductive loss. However, the extra window actually allows easier compression of the lumen of the bony otic capsule. Vibratory compression and decompression of the otic capsule is the mechanism of bone conduction, so bone conduction is actually improved by a third window. The third window gives a characteristically wide air bone gap typical of dehiscence of the superior canal. The movement of fluid in the superior canal without movement in the other canals can induce vertigo. This phenomenon of vertigo when a patient is exposed to loud sounds is referred to as the Tullio phenomenon and was part of the original description of the superior canal dehiscence syndrome by Minor et al. [14, 15]. Many other symptoms have been associated with the dehiscence, including autophony and pulsatile tinnitus. ny of these symptoms can be present in isolation, including the conductive hearing loss [16]. onductive hearing loss can mimic otosclerosis and therefore lead to an incorrect diagnosis and possibly inappropriate surgery. If a patient has otosclerosis, the presence of a significant defect in the canal can limit the effectiveness of a prosthesis. T is used to diagnose or exclude a third window [17]. defect in the canal can be appreciated in the coronal plane [18]. Presence of sufficient bone in any plane excludes the entity. defect in the superior canal is best evaluated with oblique reformatted images in the Stenvers plane perpendicular to the canal [19]. This plane gives multiple cross-sectional images through the canal. The Pöschl plane, which shows the superior canal as a ring, helps estimate the length of a dehiscence. The defect is typically along the superior arc of the superior canal along the floor of the middle cranial fossa. However, a defect can occur along the posterior limb of the canal facing the posterior fossa. The location of the defect is of obvious importance if surgical intervention is considered. lthough the superior canal defect is the most discussed, any loss in the rigid integrity of the otic capsule can produce signs and symptoms similar to those seen in superior canal dehiscence [20]. Erosion into the lateral canal by a cholesteatoma can give such 50 JR:206, January 2016

3 onductive Hearing Loss With a Normal Tympanic Membrane findings, as can posterior semicircular canal dehiscence. dehiscence between the cochlea and the carotid canal has been described, resulting in conductive hearing loss from decompression of the acoustic wave [21]. conductive component to a hearing loss in enlarged vestibular aqueduct syndrome is thought to be due to decompression of the energy through the enlarged connection of the aqueduct and the vestibule [22]. one dysplasias such as Paget disease that soften the bone may produce a similar phenomenon. Otosclerosis involving the cochlea softens the bone and could produce a third window phenomenon, but this condition would be difficult to separate from the conductive component resulting from an oval window lesion. Rarely, otosclerosis can cavitate. Even more infrequently, such cavitation may reach the cochlear or vestibular lumen and give a true third window, potentially communicating with the internal auditory canal [23, 24]. Presence of a defect does not mean that the patient will necessarily have symptoms or will benefit from surgery. Many visualized defects are incidental findings. The presence of symptoms may depend on the pliability of the dura acting as the third window membrane. orrelation with audiometric and vestibular testing is necessary to prove that a symptom is related to a particular defect. Ossicles The mobility of the ossicles is assessed by direct inspection, otoscopic pneumatic manipulation, and various acoustic reflexes. Some type of fixation (congenital, inflammatory, or otosclerotic) or ossicular discontinuity is presumed if a patient has a normal tympanic membrane and conductive hearing loss. Even though clinical evaluation is effective, the radiologist should still look for abnormality of the ossicular chain [8]. ny soft tissue against the ossicles, particularly in the upper attic away from the otoscopic view, and any other reason for fixation should be sought (Fig. 7). Tumors or even congenital cholesteatomas that are not obvious through the tympanic membrane but that give a conductive loss are rare [25]. The oval window may be congenitally small or absent. Ossification of the mallear ligaments or other bony fusions may be seen. lthough clear separation of the malleus from contiguous bone argues strongly against fusion, even a malleus that appears to be almost completely fused can still have normal mobility. The radiologist can describe the anatomy but cannot determine the precise physiology of a possible fixation. The tegmen or roof of the middle ear often appears to be abutting the head of the malleus. This relationship is optimally defined in the sagittal plane as both the axial and coronal planes are oblique to the tegmen. The fact that the tegmen appears to contact the ossicles does not mean it is responsible for a conductive hearing loss, and other explanations should be excluded. The tegmen should also be examined for potential defects or cephaloceles contacting the ossicles. However, these entities do not tend to present with isolated conductive hearing loss. Search for a defect in the caudal incus is important during the examination of a patient with a normal tympanic membrane and conductive hearing loss (Fig. 8). ecause of improvements in imaging resolution, visualization of this small structure is now feasible. The cause of such a defect is not completely settled. bsence of the lower incus may be congenital, related to aging, or the result of previous erosive or inflammatory processes. In the axial plane, the incus should be followed as it extends inferiorly to meet the stapes. ontact does not occur at the lowest tip of the long process; rather, the lenticular process extends slightly superiorly from the inferior long process to reach the capitulum or head of the stapes. In abnormal cases, the incus appears to stop blindly without apparent contact with the stapes. The structure may not be completely absent; a fibrous connection may persist. Evaluation of the inferior incus is nearly at the limit of resolution of the T scanner, but the radiologist should include a description, and in questionable cases the otolaryngologist should be alerted to the possibility of a defect in the incus. This abnormality is easily detected during surgical exploration. Facial Nerve oursing through the middle ear, the facial nerve passes just cephalad to the stapes. The nerve normally travels in its own small canal and does not contact the stapes. facial nerve schwannoma can expand the canal and impinge on the stapes, resulting in a conductive hearing loss [26, 27] (Fig. 9). Facial paralysis will raise suspicion of the diagnosis, but facial weakness is not always present with a facial nerve schwannoma; conductive loss may be the only finding. Thus, in a patient with conductive hearing loss, the location and size of the facial nerve relative to the stapes should be described. No discussion of conductive hearing loss with a normal tympanic membrane would be complete without mentioning the aberrant facial nerve. If the facial nerve in the tympanic segment is aberrant, it is almost always inferiorly positioned (Fig. 10). It can cross the oval window or migrate to a position over the promontory. The stapes may actually attach to a facial nerve directly crossing the oval window, which puts the nerve at risk if the patient is thought to have stapes fixation or otosclerosis and a surgical approach is planned. Summary n organized approach to imaging a patient with conductive hearing loss but a normal tympanic membrane should follow an algorithm slightly different from that of the patient with a cholesteatoma or a red mass seen through the tympanic membrane. Otosclerosis should be suspected, but other abnormalities must be considered. The round window should be carefully examined, as should the superior semicircular canal. The integrity of the ossicles, particularly the inferior incus, should be assessed and the facial nerve relationship to the stapes defined. cknowledgments I thank Joseph. Nadol, Jr., and Felipe Santos for their clinical input and suggestions. References 1. urtin HD, Gupta R, ergeron TR. Embryology, anatomy, and imaging of the temporal bone. In: Som PM, urtin HD, eds. Head and neck imaging. Philadelphia, P: Elsevier Mosby, 2011: Vignaud J. Temporal: fosses nasales: cavités accessoires. Paris, France: Masson, McKenna MJ, Merchant S. Disorders of bone. In: Schuknecht HF, Merchant SN, Nadol J Jr, eds. Schuknecht s pathology of the ear. Shelton, T: People s Medical Publishing House, 2010: Sakai O, urtin HD, Hasso N, Swartz JD. Otosclerosis and dysplasias of the temporal bone. In: Som PM, urtin HD, eds. Head and neck imaging. Philadelphia, P: Elsevier Mosby, 2011: Quesnel M, Moonis G, ppel J, et al. orrelation of computed tomography with histopathology in otosclerosis. Otol Neurotol 2013; 34: Sakai O, urtin HD, Fujita, Kakoi H, Kitamura K. Otosclerosis: computed tomography and magnetic resonance findings. m J Otolaryngol 2000; 21: Swartz JD, Faerber EN, Wolfson RJ, Marlowe FI. Fenestral otosclerosis: significance of preoperative T evaluation. Radiology 1984; 151: ance M. When is a conductive hearing loss not a JR:206, January

4 urtin conductive hearing loss? auses of a mismatch in airbone threshold measurements or a pseudoconductive hearing loss. J Otolaryngol 2004; 33: Linder TE, Ma F, Huber. Round window atresia and its effect on sound transmission. Otol Neurotol 2003; 24: Martin, Tringali S, ertholon P, Pouget JF, Prades JM. Isolated congenital round window absence. nn Otol Rhinol Laryngol 2002; 111: lifford R, Fagan P, Doust D. Isolated congenital round window absence. J Laryngol Otol 1990; 104: Richards SH. ongenital absence of the round window treated by cochlear fenestration. lin Otolaryngol llied Sci 1981; 6: Nadol J Jr. Histopathology of residual and recurrent conductive hearing loss after stapedectomy. Otol Neurotol 2001; 22: Minor L. Superior canal dehiscence syndrome. m J Otol 2000; 21: Minor L, Solomon D, Zinreich JS, Zee DS. Sound- and/or pressure-induced vertigo due to bone dehiscence of the superior semicircular canal. rch Otolaryngol Head Neck Surg 1998; 124: Mikulec, McKenna MJ, Ramsey MJ, et al. Superior semicircular canal dehiscence presenting as conductive hearing loss without vertigo. Otol Neurotol 2004; 25: elden J, Weg N, Minor L, Zinreich SJ. T evaluation of bone dehiscence of the superior semicircular canal as a cause of sound- and/or pressureinduced vertigo. Radiology 2003; 226: ranstetter F 4th, Harrigal, Escott EJ, Hirsch E. Superior semicircular canal dehiscence: oblique reformatted T images for diagnosis. Radiology 2006; 238: urtin HD. Superior semicircular canal dehiscence syndrome and multi-detector row T. Radiology 2003; 226: Merchant SN, Rosowski JJ. onductive hearing loss caused by third-window lesions of the inner ear. Otol Neurotol 2008; 29: Neyt P, Govaere F, Forton GE. Simultaneous true stapes fixation and bilateral bony dehiscence between the internal carotid artery and the apex of the cochlea: the ultimate pitfall. Otol Neurotol 2011; 32: Merchant SN, Nakajima HH, Halpin, et al. linical investigation and mechanism of air-bone gaps in large vestibular aqueduct syndrome. nn Otol Rhinol Laryngol 2007; 116: ou-ssaly W, Mukherji S, Srinivasan. ilateral cavitary otosclerosis: a rare presentation of otosclerosis and cause of hearing loss. lin Imaging 2013; 37: Makarem O, Hoang T, Lo WW, Linthicum FH Jr, Fayad JN. avitating otosclerosis: clinical, radiologic, and histopathologic correlations. Otol Neurotol 2010; 31: Kim SH, ho YS, hu HS, Jang JY, hung WH, Hong SH. Open-type congenital cholesteatoma: differential diagnosis for conductive hearing loss with a normal tympanic membrane. cta Otolaryngol 2012; 132: Juliano F, Maya MM, Lo WW, Kovanlikaya I. Temporal bone tumors and cerebellopontine angle lesions. In: Som PM, urtin HD, eds. Head and neck imaging. Philadelphia, P: Mosby Elsevier, 2011: May M. Tumors involving the facial neve. In: May M, ed. The facial nerve. New York: Thieme, 1986: PPENDIX 1: heckpoints in Patients With onductive Hearing Loss and Normal Tympanic Membrane Otosclerosis Round window occlusion Third window phenomenon Oval window atresia Ossicular fixation or defect Integrity of inferior long process of incus ttic and tegmen Low-lying lesion or cephalocele in attic not visible through tympanic membrane Facial nerve position and size in patients with tumor Fig. 1 one-beam T examination of 27-year-old woman with tinnitus shows normal findings., Technologist sets standard axial plane (dashed line) by connecting dots of anterior and posterior limbs (arrows) of lateral semicircular canal on sagittal T image., Standard axial image obtained in plane along line generated in shows lateral canal as ring. Facial nerve passes just anteriorly., Standard axial image obtained in plane parallel and caudad to though footplate (arrow) and crura of stapes. = cochlea, M = malleus. (Fig. 1 continues on next page) 52 JR:206, January 2016

5 onductive Hearing Loss With a Normal Tympanic Membrane D Fig. 1 (continued) one-beam T examination of 27-year-old woman with tinnitus shows normal findings. D, Standard coronal image obtained in plane perpendicular to line in and through cochlea. E, Standard coronal image obtained in plane posterior to D through footplate (large arrow) of stapes, facial nerve canal (small arrow), and lateral semicircular canal (LS). F, Standard coronal image obtained in plane posterior to E at level of round window (arrow). SS = superior semicircular canal. E Fig. 2 Image of temporal bone shows Pöschl plane and Stenvers plane alignment relative to superior canal in axial plane. oth planes are approximately 45 from both coronal and sagittal planes. For Pöschl plane, reformats are created along line (dotted line) connecting dots of anterior and posterior limbs of superior semicircular canal (arrows). Stenvers plane (white line) is perpendicular to Pöschl plane. Fig. 3 one-beam T examination of 24-year-old woman with otosclerosis and conductive hearing loss that had progressed for at least 5 years., xial image shows demineralized bone (arrow) anterior to oval window and impinging on footplate of stapes (S). ompare demineralized bone with remainder of otic capsule., xial image obtained in plane inferior to. Focus of demineralized bone (arrow) is seen along basilar turn of cochlea that would be considered retrofenestral or cochlear otosclerosis. (Fig. 3 continues on next page) F JR:206, January

6 urtin D Fig. 3 (continued) one-beam T examination of 24-year-old woman with otosclerosis and conductive hearing loss that had progressed for at least 5 years., xial image obtained in plane inferior to. ir (arrow) is seen in round window niche against round window membrane. D, oronal reformatted image just anterior to oval window. Focus of demineralized bone (arrow) is contrasted against denser bone of otic capsule. Fig year-old man with long-standing and progressive conductive hearing loss. Stapes wire piston prosthesis (arrow) was inserted into stapedotomy and attached to long process of incus. Medial piston part of prosthesis is not as dense as wire. Fig. 5 MDT images in 47-year-old woman with long-standing conductive hearing loss show otosclerosis with closure of round window., xial image through round window shows complete obliteration of round window (arrow) by demineralized bone of otosclerosis. ompare with Figure 3., oronal image through round window (arrow) shows that window is completely closed and no air reaches round window membrane. 54 JR:206, January 2016

7 onductive Hearing Loss With a Normal Tympanic Membrane Fig. 6 one-beam T examination in 52-year-old woman with dizziness and conductive hearing loss shows superior semicircular canal dehiscence., oronal plane image shows apparent defect (arrow) in superior semicircular canal., xial pyramidal (Pöschl) plane image perpendicular to axis of petrous bone parallel to plane of superior semicircular canal. Large defect (between arrows) is seen along superior aspect of canal., Stenvers plane image along axis of temporal bone perpendicular to superior canal shows cross-section of canal and large defect (arrow). Fig. 7 one-beam T examination in 42-year-old woman with reported congenital hearing loss in right ear and normal hearing in left ear. In right ear, tympanic membrane is normal and malleus is mobile. coustic reflex absent in right ear indicates stapes fixation. ongenital bony fusion of malformed incus and stapes is seen., oronal plane image shows bony mass just inferior to facial nerve (VII 2 ) covering oval window niche. Footplate is seen in normal oval window., Oblique (Pöschl) plane image shows bony mass extending toward oval window but not touching footplate (arrow) of stapes. Malleus (M) was mobile although bone touches head of malleus. RW = round window, J = jugular foramen. JR:206, January

8 urtin Fig. 8 one-beam T examination in 46-year-old woman with conductive hearing loss, sense of vibration in ear, and history of infection with subsequent tympanostomy tube placement in childhood. Patient had no or resorbed lower long process of incus., xial T image shows malleus (M) and incus (I)., xial T image obtained in plane just inferior to. Long process (arrow) is visualized., xial T image obtained in plane just inferior to. Lower long process is absent. It should continue inferiorly to meet stapes. rrow indicates posterior crus of stapes. Fig. 9 MDT image in 31-year-old woman with facial nerve schwannoma causing conductive hearing loss but no facial weakness. Patient had history of facial paralysis many years earlier that was presumed to be ell palsy, but she experienced no residual defect. Schwannoma enlarges facial nerve canal (arrow) and impinges on stapes. Fig. 10 MDT image in 27-year-old woman with conductive hearing loss since childhood. Patient had normal facial function but congenital aberrant facial nerve crosses oval window. oronal plane shows aberrant location of facial nerve (arrow). Stapes attaches directly to abnormally placed nerve. 56 JR:206, January 2016