Temporal Bone CT Scans Research Articles

Unilateral internal auditory canal stenosis with progressive facial weakness

Internal auditory canal (IAC) stenosis is a rare cause of sensorineural hearing loss. Patient may present with symptoms of progressive facial nerve palsy, hearing loss, tinnitus and giddiness. High resolution temporal bone CT-scan and magnetic resonance imaging (MRI) are the important tools for diagnosis. No specific management has been devised. Here is presentation of a case of unilateral (left) IAC stenosis with profound hearing loss and progressive House Brackmann Grade III-IV facial weakness. The diameter of the IAC was less than 2 mm on high resolution temporal bone computed tomography (HRCT) scan. It was managed by facial nerve decompression by translabyrinthine approach in an attempt to prevent further deterioration of facial palsy. DOI: http://dx.doi.org/10.3329/bjo.v18i2.12014 Bangladesh J Otorhinolaryngol 2012; 18(2): 179-182

Fistule périlymphatique (FPL) post-traumatiques : évolution fonctionnelle après prise en charge chirurgicale à propos d’une série de 33 cas

Middle ear cholesteatoma is a destructive lesion that can potentially erode the bone. Cholesteatoma is a clinical diagnosis in the vast majority of cases. Patients must be systematically investigated for the presence of signs suggestive of complications, the most common of which is labyrinthine fistula. However, the clinical features of labyrinthine fistula are inconstant and the fistula sign may sometimes be negative. CT scan of the petrous temporal bone is performed systematically to specify the site and extension of the cholesteatoma, and to assess the extent of osteolysis that can result in exposure of the membranous labyrinth. Surgical treatment has three main objectives: complete resection of the cholesteatoma, which is the only way to avoid residual cholesteatoma, prevention of recurrence by an adapted, preferably one-step, technique, and restoration of good quality hearing. Hydrodissection of the cholesteatoma matrix in the presence of labyrinthine fistula is a simple technique that can achieve the three main general objectives of cholesteatoma surgery.

Audiological and radiological characteristics of a family with T961G mitochondrial mutation

Objective: The aim of this study was to describe audiological and radiological characteristics, and other secondary aspects, in a family carrying a T961G mutation in the 12S rRNA mitochondrial gene. Design: Case report. Study sample: Six members of a family participated in an audiological evaluation that included pure-tone audiometry, immittance tests, auditory brainstem responses (ABR), and otoacoustic emissions (OAE). The radiological evaluation was conducted through temporal bone CT scans using a Toshiba 16 channels Aquilon Spirale. Neuropsychiatric evaluation was also administered. Results: Three participants were diagnosed with severe sensorineural hearing loss of cochlear origin and cochlear malformations visible in CT scans. One participant had a mild mixed-hearing loss and no cochlear malformations. Two participants had normal audiological and radiological findings. Conclusions: We believe our study can provide helpful insight on the clinical findings of a rare mutation, of which few data have been presented in literature.

Diagnóstico por imagen de las lesiones benignas del conducto auditivo externo

Introduction and objectivesBenign lesions of the external auditory canal (EAC) are an infrequent cause of temporal bone CT scan requests. We are not usually well versed in the different pathologies located in the EAC, perhaps because it is “only” a conduit and the relevant anatomical structures are located in the middle and inner ear.Our objective was to improve knowledge of this structure by reviewing the different benign conditions found in this location. MethodsWe reviewed the CT studies from 2 years (January 2010 through January 2012), selecting those containing lesions in the EAC. To complement this, due to the importance of these lesions, these medical histories were then analysed considering the presentation and otoscopic examination findings. ResultsThe lesions were classified according to their diagnoses: exostosis, osteoma, cholesteatoma, keratosis obturans, haemangioma, non-neoplastic aural polyp, first branchial cyst and dermatologic disease (malignant external otitis). The presence of EAC occupation in the otological examination and chronic otorrhea as the symptom of presentation were the most relevant exploratory and clinical findings. ConclusionsBenign EAC lesions are an uncommon and seldom studied cause of temporal bone CT scan requests. Knowing the most relevant clinical and radiological findings is necessary for their proper diagnosis.

Fracture violating the otic capsule following paediatric head trauma: Association of a pneumolabyrinth with a pneumo-internal auditory canal and pneumoencephaly

Introduction : Pneumolabyrinth is the presence air within the labyrinth and is a radiological diagnosis. A perilymphatic fistula (PLF) is an abnormal communication between the middle ear and inner ear and is usually discovered upon surgical ear exploration. These conditions could also occur following a temporal bone fracture, or in idiopathic cases. We compare air location of pneumolabyrinth between our case report and others cases reported in literature, about post-traumatic pneumolabyrinth in a paediatric population. Case report and results : 16 cases overall of pneumolabyrinths in the paediatric population have been described in the literature, only two of which was associated with a pneumo-internal auditory canal. We present a case of a huge pneumolabyrinth following head trauma which occurred in a 2 year-old boy. This pneumolabyrinth is managed by surgery. There was no response on brainstem auditory evoked potentials before surgery and 4 month after. Conclusion : A clear otorrhea after a traumatism can come from a PLF or a cerebrospinal leak. This case presents both conditions. To differentiate a cerebrospinal fluid leak from a perilymphatic fistula, new biological test could be a help. A pneumolabyrinth visualised on a temporal bone CT-scan strongly suggests a perilymphatic fistula. Performing an exploratory tympanotomy makes the definitive diagnosis. There are two main reasons for repairing a PLF: to improve a patient's auditory and vestibular symptoms, and to minimize the risk of developing meningitis. Patients with a pneumolabyrinth, with air present in both the scala tympani and vestibuli, had poor hearing outcomes.

Venous malformations of the temporal bone are a common feature in CHARGE syndrome

CHARGE (Coloboma of the eye, Heart defects, Atresia of the choanae, Retardation of growth and/or development, Genital and/or urinary abnormalities, and Ear abnormalities and/or deafness) syndrome is a genetic disorder with prominent otolaryngologic features including choanal atresia and inner ear malformations. Recent experience with venous malformations during cochlear implant surgery prompted this study to define the spectrum of venous abnormalities in CHARGE and their surgical implications in otology. Retrospective review of medical and radiologic records from databases of patients with CHARGE syndrome from three tertiary care academic medical centers. Eighteen patients with CHARGE for whom temporal bone CT scans were available were included in the review. Venous anomalies of the temporal bone were present in 10 of 18 (56%) patients. The most common were large emissary veins (n = 5). In two of these cases, these veins were associated with an ipsilateral a hypoplastic sigmoid sinus or jugular foramen. Other abnormalities included an aberrant petrosal sinus, venous lakes in proximity to the lateral venous sinus, condylar canal veins, and jugular bulb abnormalities, including a high riding bulb obscuring the round window niche and a dehiscent jugular bulb. In four of six patients undergoing cochlear implantation, the course of the aberrant vessel necessitated a change in the surgical approach, either during mastoidectomy or placement of the cochleostomy. Temporal bone venous abnormalities are a common feature in CHARGE syndrome. The pattern of venous abnormality suggests that there is a failure of the sigmoid sinus/jugular bulb to fully develop, resulting in persistence of emissary veins. Recognition of these abnormal venous structures during otologic surgery is critical to avoiding potentially catastrophic bleeding.

Coronal CT scan measurements and hearing evolution in enlarged vestibular aqueduct syndrome

ObjectiveTo assess the correlation between the enlarged vestibular aqueduct (EVA) diameter and (1) the hearing loss level (mild, moderate, severe and profound and (2) the hearing evolution. The secondary objective was to obtain measurement limits on the coronal plane of the temporal bone CT scan for the diagnosis of EVA. MethodsRetrospective study in a tertiary pediatric center. Mastoid CT scans were reviewed to measure the VA diameter at its midpoint and operculum on axial and coronal planes in a pathologic and normal population. We used their serial audiograms to assess the evolution of hearing. Results101 EVA was identified out of 1812 temporal bones CT scan from our radiologic database in 8 years. Bone conduction was stable after a mean follow-up of 40.9±32.9 months. PTA has been the most affected in time by the EVA (p=0.006). No correlation was identified between impedancemetry and the diameter of the EVA. On the diagnostic audiogram, 61% of hearing loss were in the mild and moderate hearing levels; at the end of the follow-up 64% of hearing loss are still in the mild and moderate hearing levels. The cut-off values for the coronal midpoint and operculum planes on the CT scan to diagnose an EVA are 2.4mm and 4.34mm respectively. ConclusionsConductive or mixed hearing loss might be the first manifestation of EVA. Coronal CT scan cuts can provide additional information to evaluate EVA especially when axial cuts are not conclusive.

Tuberculous Mastoiditis: Report of an Uncommon Case in Morocco

Although tuberculosis is a major problem of public health in Morocco, the tuberculous mastoiditis remains extremely rare, and its diagnosis is often delayed. We report here the case of a 3-year-old child who had unusual chronic left mastoiditis and retro-auricular fistula, associated with spontaneous discharge of bony sequestrum. CT scan of temporal bones showed complete destruction of left mastoid cells. A left mastoidectomy confirmed the tuberculous mastoiditis diagnosis after histopathological examination. The clinical outcome was favorable after anti-tuberculosis treatment. Otologic tuberculosis of the ear is well described in the literature and symptoms include chronic otorrhea with audio-vestibular symptoms. The specificity of this case is that the child had an isolated involvement of the mastoid with spontaneous bony sequestrum discharge, but without otorrhea.

Experimental Study and Optimization of Scan Parameters That Influence Radiation Dose in Temporal Bone High-Resolution Multidetector Row CT

MDCT has some specific scan parameters that may systematically increase or decrease radiation dose to patients. This study explored the scan protocol parameters that impact radiation dose in temporal bone MDCT and determined the optimal scan parameters that balance radiation dose with diagnostic image quality. Using exsomatized cadaveric heads, traditional axial scanning, and helical scanning were performed with different detector collimations. Helical scans of the same scan region were then acquired by using the determined optimal detector collimation and various tube voltages, whereas other scan parameters remained fixed. Next, the scans were repeated by using various tube current-time products by using the determined optimal tube voltage. Last, with fixed tube current-time product, the scans were repeated with various pitches. All thin-section, helically acquired scans were reformatted to axial and coronal images with respect to the relevant scanning baseline. In each of the image volumes, the mean and SD HU values in regions of interest were measured in the central section of the internal auditory canal, and CNR values were calculated. In agreement with theory, wider detector collimations such as 16 × 0.625 mm and 64 × 0.625 mm were associated with lower radiation doses than narrower collimations due to their lower overbeaming and higher geometric efficiency. In helical scanning, the detector collimation of 16 × 0.625 mm had higher image quality and the minimum DLP. Axial and coronal images acquired by using a 140-kVp tube voltage had significantly lower noise than scans acquired at 120 or 80 kVp with equivalent volume CT dose index. Diagnostic image quality was achieved when using a minimum tube current-time product of 120 mAs. Noise, CNR, and dose were jointly optimized with a pitch of 0.685. Temporal bone CT scanning parameters may be optimized by following a systematic procedure that allows for the optimization of diagnostic image quality and the minimization of radiation dose. One such procedure for a particular 64-section MDCT scanner has been presented.

Anatomic Variants on Congenital Computed Tomography in Congential Aural Atresia

Objective: Report incidence of anatomic variants in temporal bone CT scans with congenital aural atresia (CAA) or external auditory canal stenosis (EACS). Anatomic variants include: inferiorly displaced tegmen, malleus/incus complex (MIC) directly lateral to stapes, facial nerve obstruction at oval window (OW) and middle ear, middle ear area, incudostapedial (IS) joint angle. Method: Prospective anatomic study of 134 CT scans (102 children, 32 bilateral) of CAA/EACS, graded by a blinded neuroradiologist. Both Jahrsdoerfer and absence or presence of new/refined anatomic considerations were graded. There were 32 atresiaplasty and 70 nonsurgical patients. Surgical and audiological data were reviewed retrospectively for anatomic correlations related to outcomes. Results: Prevalence of anatomical variants: inferiorly displaced tegmen X (X%), MIC directly lateral to stapes Y (Y%), facial nerve obstructed access to oval window Z (Z%), and middle ear B (B%). Large MIC obstructing stapes access (5/7 patients) with increased intra-operative difficulty. Mean middle ear area DD (range, 0.07 to 0.86mm2) and mean IS joint angle FF (range, 50°-147°). Trend toward improved outcomes with: normal tegmen, facial nerve favorable to OW, or non-obstructing MIC. No statistically significant clinical correlations for anatomic factors including Jahrsdoerfer grading. Conclusion: Large obstructing MIC increases the difficulty of atresiaplasty. There is a trend showing improved outcomes with normal tegmen, facial nerve favorable to oval window, or nonobstructing MIC. A larger atresiaplasty cohort is needed since the number of cases was insufficient to demonstrate statistical significance. Nonetheless, the frequency of these new/refined anatomic variants has been more clearly delineated. The presence of these anatomic variants may possibly influence the decision for or against atresiaplasty.

Low-Dose Temporal Bone CT in Infants and Young Children: Effective Dose and Image Quality

The temporal bone is ideal for low-dose CT because of its intrinsic high contrast. The aim of this study was to retrospectively evaluate image quality and radiation doses of a new low-dose versus a standard high-dose pediatric temporal bone CT protocol and to review dosimetric data from the literature. Image quality and radiation doses were compared for 38 low-dose (80 kV/90-110 mAs) and 16 high-dose (140 kV/170 mAs) temporal bone CT scans of infants to 5-year-old children. The CT visualization quality of 23 middle and inner ear structures was subjectively graded by 3 neuroradiologists and 3 otologists by using a 5-point scale with scores 1-2 indicating insufficient and scores 3-5 indicating sufficient image quality. Effective doses of local and literature-derived protocols were calculated from dosimetric data by using NRPB-SR250 software. Insufficient image-quality scores were more frequent in low-dose scans versus high-dose scans, but the difference was only statistically significant for otologists (6.0% versus 3.4%, P = .004) and not for neuroradiologists (1.2% versus 0.7%, P = .84). Image quality was critical for small structures (such as the stapes or lamella at the internal auditory canal fundus). Effective doses were 0.25-0.3 mSv for low-dose scans, 1.4-1.8 mSv for high-dose scans, and 0.9-2.6 mSv for literature-derived protocols. The image quality of the new low-dose protocol remains diagnostic for assessing middle and inner ear anatomy despite a 3- to 8-fold dose reduction over previous and literature-derived protocols. However, image quality of small structures is critical and may be perceived as insufficient.

Anatomic Analysis of the Mastoid Tegmen

To examine the dural slope shapes and slope depths in different axes in the mastoid. These are important for surgical guidance. Setting-Tertiary care otologic center. Patients/materials-105 temporal bone CT scans were used from subjects who had undergone High Resolution Temporal Bone CT scanning for CSOM, using the non-diseased ear scans. In addition, 21 "diseased side" temporal bones were included. Scans were reconstructed in 3D using Amira software to examine tegmen shapes. The highest and lowest points on the tegmen were measured along 4 axes, 2 in the coronal plane (latero-medial axes posteriorly and anteriorly [L-M ant and L-M post]), and 2 in the sagittal plane (posterio-anterior axes medially and laterally [P-A med and P-A lat]). The highest and lowest point difference was labeled ΔH. We also measured the height from the superior external canal to the tegmen. There was a unimodal distribution in the ΔH variable for all axes measured. Means and (SD) in mm for ΔH are as follows: L-M post 4.1 (2), L-M ant 2.9 (2.2), P-A med 6.5 (1.9), P-A lat 5.4 (2.2). Tegmen-EAC lat and med height means were 8.4 and 9.7 mm respectively. Representative 3D shapes are presented. There appears to be a unimodal distribution of mastoid tegmen shapes and sizes, without clustering into subpopulations. The tegmen slopes have real implications for surgical exploration and disease eradication. A Tegmen classification scheme is presented.

Observations of an ACR CT Accreditation Program Reviewer

As a reviewer for the ACR CT accreditation program for about 4 years, I have had the opportunity to observe a broad spectrum of work from across the country that I would otherwise have not been privy to in my private radiology practice. Unfortunately, communication with the submitting group is only available through the ACR evaluation. Because there is no mechanism to discuss my overall mpressions with the radiology ommunity at large, I have taken his opportunity to discuss my bservations of submitted mateial with the goal of improving mage quality, decreasing radiaion exposure, and passing ACR ccreditation. Most of the submissions to the CR CT accreditation program hat I review take advantage of the ewer features available on curent-generation scanners (under arious names depending on the anufacturer), such as dose modlation, contrast bolus detection, nd acquisition of multiple thinection images with multiplanar eformatting. Regrettably, basic eatures of the scanners are undeused. A recurrent example is the imited use of different recontruction algorithms. Most curent and recent generation scaners offer different reconstruction lgorithms (or filters) to maxiize soft tissue or bony detail or ptimize for lung imaging. Scaners can reconstruct the same imge data set with multiple algoithms, often automatically. Yet, ead CT scans are filmed with soft tissue and bone windows from the same soft tissue reconstruction. Chest CT scans are filmed at soft tissue and lung windows from the same soft tissue reconstruction without the benefit of a separate lung reconstruction. Field of view is initially set at the time of scanning but can be adjusted after image acquisition to optimally display anatomy, yet sinus CT scans are submitted with large fields of view, minimizing the anatomy of interest. Temporal bone CT scans can be reconstructed bilaterally with a field of view as small as 9 to 10 cm (using a bone algorithm) to maximize the display of small anatomic structures. Submitted cases often do not take advantage of this capability. As mentioned above, many of the body CT cases use some type of dose modulation technique to minimize radiation exposure to the patient. Other simpler methods to reduce radiation exposure are overlooked, such as protocols with multiple series. Many scans submitted have 3 or even 4 acquisitions, such as routine abdomen CT protocols consisting of noncontrast, arterial, venous, and delayed acquisitions. Eliminating one or more acquisitions would decrease radiation dose by 25% to 75%. One or two acquisitions, depending on the indication, are usually sufficient. Many scans acquire images beyond the area of interest, such as axial sinus CT obtaining images above the frontal sinuses or head CT scans with images acquired below the

Safety and patient selection of totally implantable hearing aid surgery: Envoy system, Esteem

Patient's low compliance of conventional hearing aids has lead to innovation of totally implantable hearing devices such as Esteem, Envoy system. This study was designed to evaluate safety of device implantation, patient's hearing gain, importance of anatomic landmarks, and to describe suitable criteria for patient selection. Via a non-randomized controlled clinical trial, ten patients with moderate-to-severe sensorineural hearing loss were implanted from 2007 to 2009. Mean follow-up period was 29.4months. Correlation of pre-operative temporal bone CT scan anatomy with postoperative outcome was evaluated. Except one, all other implanted devices are active and patients' overall average hearing gain are similar to conventional hearing aids (10-22dB), but patients reported relatively better subjective sound quality compared with their pre-operative conventional hearing aids. One implanted device was explanted in a patient due to facial weakness and low-hearing gain. Revision surgery was done successfully in another patient secondary to excessive bone growth. Totally implantable hearing device surgery seems to be relatively safe and correct patient selection could lead to good outcomes. Lateral location of facial nerve, sclerotic mastoid air cells and narrow facial recess space seems to be related to postoperative complications.

Tympanoplasty Results in an Ethnically Diverse Patient Population

Methods: Adult patients who underwent type I tympanoplasty from January 2009 through July 2010 were eligible. Charts were reviewed for preand postoperative drum status, patient characteristics, temporal bone CT scans and audiologic data. The primary outcome measure was successful repair, defined as an intact drum at last follow-up visit. A secondary outcome measure was postoperative hearing improvement, defined as a difference between airconduction and bone-conduction pure-tone averages of less than 20 dB.

Congenital conductive hearing loss and multiple synostosis syndrome with analysis of temporal bone CT scan findings

We present the case of a mother and four children displaying signs of Multiple Synostosis Syndrome (SYNS1) associated with conductive hearing loss. The intra-familial phenotypic variation is due to variable penetrance, which is typical of this syndrome. The child with the most significant hearing loss showed lucency of the otic capsule on temporal bone CT. There is no evidence of this phenomenon associated with SYNS1 in the literature. CT scanning can diagnose certain ossicular chain abnormalities, removing the need for tympanotomy under general anaesthetic. Syndromic hearing loss is progressive and should be monitored where appropriate.

Non-syndromic bilateral enlarged vestibular aqueducts in two siblings

Abstract Enlarged vestibular aqueduct is one of the most frequent inner ear malformations with early manifested sensorineural hearing loss. It is often associated with Pendred syndrome. The non-syndromic familial enlarged vestibular aqueduct entity is less described with only a few cases reported in the literature. It is thought to be a varying presentation on the phenotypic spectrum of genetic mutation in the same locus of chromosome 7q31. The familial inheritance has been suspected to be autosomal recessive. In this case report, we present a patient who presented to the clinic with hearing loss after blunt head trauma with a soccer ball. Suspected enlarged vestibular aqueduct was confirmed to be bilateral on CT scan of the temporal bones. Additional inquiry into the family history revealed that her sister also had bilateral sensorineural hearing loss at an early age. Unpredictably, bilateral enlarged vestibular aqueducts were confirmed in the sister with similar imaging modality. The clinical presentation, diagnosis, and treatment strategies are reviewed along with the current literature.

Radiation dose to the lens using different temporal bone CT scanning protocols.

Temporal bone CT is performed frequently in clinical practice. At the same time, the eye lens are exposed to ionizing radiation without any useful diagnostic information delivered. Our aim was to investigate the radiation dose to the lens of the eye by using temporal bone CT scanning with different protocols. Direct axial and coronal CT by using a conventional sequential scanning mode (140 kV, 220 mAs/section, 1.25-mm thickness, 1.25-mm increment, 16 x 0.625 mm collimation, the glabellomeatal line as a scanning baseline), a routine helical scanning mode (140 kV, 220 mAs/section, 0.315 pitch, 0.67-mm thickness, 0.33-mm increment, 16 x 0.625 collimation, the orbitomeatal line as a scanning baseline), and a modified helical scanning mode (acanthiomeatal line as a scanning baseline; other parameters, same as above) was performed on an exsomatized cadaveric head. CTDI(vol) and DLP were recorded for each scanning mode, and effective doses were calculated. Organ doses for the lens were measured with TLDs. When the sequential scanning mode was used, the gross effective dose was 1.21 mSv and the organ dose to the lens was 50.96 and 1.73 mGy, respectively, for direct axial and coronal imaging. The effective dose was 0.803 mSv in routine helical scanning, while the lens dose was 40.17 mGy. With the modified helical scanning mode, the effective dose was as same as that for the routine helical scanning, but the lens dose was reduced significantly to 10.33 mGy. The effective doses resulting from sequential axial and coronal scanning were 1.51 times higher than the dose from helical scanning, and the lens dose was 1.31 times higher. With the modified helical scanning mode, thinner section images could be used to reformat axial, coronal, and sagittal images with a further 74.3% reduction in lens dose beyond that achieved with the conventional helical protocol.

Comprehensive molecular etiology analysis of nonsyndromic hearing impairment from typical areas in China

BackgroundEvery year, 30,000 babies are born with congenital hearing impairment in China. The molecular etiology of hearing impairment in the Chinese population has not been investigated thoroughly. To provide appropriate genetic testing and counseling to families, we performed a comprehensive investigation of the molecular etiology of nonsyndromic deafness in two typical areas from northern and southern China.MethodsA total of 284 unrelated school children with hearing loss who attended special education schools in China were enrolled in this study, 134 from Chifeng City in Inner Mongolia and the remaining 150 from Nangtong City in JiangSu Province. Screening was performed for GJB2, GJB3, GJB6, SLC26A4, 12S rRNA, and tRNAser(UCN) genes in this population. All patients with SLC26A4 mutations or variants were subjected to high-resolution temporal bone CT scan to verify the enlarged vestibular aqueduct.ResultsMutations in the GJB2 gene accounted for 18.31% of the patients with nonsyndromic hearing loss, 1555A>G mutation in mitochondrial DNA accounted for 1.76%, and SLC26A4 mutations accounted for 13.73%. Almost 50% of the patients with nonsyndromic hearing loss in these typical Chinese areas carried GJB2 or SLC26A4 mutations. No significant differences in mutation spectrum or prevalence of GJB2 and SLC26A4 were found between the two areas.ConclusionIn this Chinese population, 54.93% of cases with hearing loss were related to genetic factors. The GJB2 gene accounted for the etiology in about 18.31% of the patients with hearing loss, SLC26A4 accounted for about 13.73%, and mtDNA 1555A>G mutation accounted for 1.76%. Mutations in GJB3, GJB6, and mtDNA tRNAser(UCN) were not common in this Chinese cohort. Conventionally, screening is performed for GJB2, SLC26A4, and mitochondrial 12S rRNA in the Chinese deaf population.

Demineralization of the Otic Capsule in Otosclerosis (Otospongiosis)

A 34-year old Filipina presents with bilateral progressive hearing loss and tinnitus of three years' duration. Otologic examination reveals normal external auditory canals and tympanic membranes, with good tympanic membrane mobility on pneumatic otoscopy. Standard audiometric examination shows a bilateral moderate conductive hearing loss. Temporal bone CT imaging reveals the presence of a focal region of bone demineralization involving the dense bone of the otic capsule surrounding the cochlear lumen (Figure 1), a finding consistent with a diagnosis of active otospongiosis.  The diagnosis was confirmed by visualization of an otosclerotic focus during transcanal middle ear exploration, where stapedectomy with placement of a stainless steel stapes prosthesis was performed. Otosclerosis is a condition unique to the temporal bone characterized by abnormal resorption and deposition of bone in the otic capsule and ossicles. Although it occurs more rarely in Asiatic populations compared to Europeans, Americans of Caucasian origin and Indians, it must be considered in patients presenting with primarily conductive hearing loss, especially if there is bilateral involvement. CT imaging of the temporal bone may help to differentiate this condition from other causes of conductive hearing loss, such as tympanosclerosis and bony epitympanic fixation of the ossicular chain from chronic infection and inflammation of the middle ear. One must be cognizant of the fact that a normal temporal bone CT scan does not rule a diagnosis of otosclerosis, because an inactive, highly sclerotic focus that appears as a uniform hyperdense mass may be difficult to distinguish from the normal compact labyrinth capsule (1). Other causes of otic capsule demineralization include osteogenesis imperfecta, Paget disease, otosyphilis, and Camurati-Engelmann disease. These may be differentiated by their individually characteristic patterns of bone involvement and evidence of disease in other organ systems.2 &nbsp