Computed tomographic 3D analysis of the cochlear aqueduct-potential and limitations of clinical imaging.

Background: The cochlear aqueduct (CA), which connects the scala tympani and the subarachnoid space, and its accompanying structures appear to have a significant relevance during cochlear implantation and an accurate visualization in clinical imaging is of great interest. Aims and Objective: This study aims to determine which potential and limitations clinically available imaging modalities have in the visualization of the CA. Methods: Micro-CT, flat-panel volume computed tomography with and without secondary reconstruction (fpVCT, fpVCTseco) and multislice computed tomography (MSCT) of 10 temporal bone specimen were used for 3D analysis of the CA. Results: FpVCTseco proved superior in visualizing the associated structures and lateral portions of the CA, which merge into the basal turn of the cochlea. All clinical imaging modalities proved equal in analyzing the length, total volume of the CA and its area of the medial orifice. Conclusion: The choice of the most accurate clinical imaging modality to evaluate the CA and its associated structures depends on the clinical or scientific question. Furthermore, this study should provide a basis for further investigations analyzing the CA.

Why did we encounter gusher in a stapes surgery case? Was it enlarged medial aperture of the cochlear aqueduct?

BACKGROUND AND PURPOSE: Preoperative prediction of cerebrospinal fluid (CSF) gusher is important for stapes surgery. According to the current opinion settled among otologists and radiologists, the issues of whether enlarged cochlear aqueduct might be a cause of CSF gusher in stapes surgery and which segment of the aqueduct should be taken into account to diagnose enlarged cochlear aqueduct in computerized tomography (CT) are controversial. The case we encountered led us to hypothesize that enlarged cochlear aqueduct might cause CSF gusher in stapes surgery and that shape and diameter of medial aperture of the cochlear aqueduct are important in this prediction. METHODS AND RESULTS: Enlarged medial aperture of the cochlear aqueduct with a shape differed from that of the other side was retrospectively diagnosed in thin-slice CT in a patient who had been undergone middle ear and stapes surgery for conductive hearing loss. This finding went unnoticed in preoperative CT. In the small fenestra stapedotomy operation, CSF gusher occurred through opening in the ill-defined, fixed and thickened stapes footplate. A piece of temporalis fascia and reshaped incus were appropriately placed which stopped the gusher. Re-evaluation of preoperatively taken CT showed that anterior-posterior and superior-inferior diameters of the medial aperture were 11.7 mm and 2.87 mm in CSF gusher side versus 2.95 mm and 1.88 mm on the other side, respectively. Its shape in gusher side differed from that of the other side. CONCLUSION: This report is the first to show video-documented CSF gusher in a patient with enlarged medial aperture of the cochlear aqueduct. It appears to be plausible to propose that these findings have to change the otologists' and radiologists' perspective to the cochlear aqueduct. It can be deduced that difference in shapes of the medial aperture in both sides might be an indicator of potential CSF gusher.

Oval window perilymph fistula in child with recurrent meningitis and unilateral hearing loss.

A 2-year-old boy presented to Ears, Nose and Throat (ENT) surgeons with unilateral hearing loss. Following a prodrome of upper respiratory tract infection (URTI), he developed two episodes of pneumococcal meningitis in quick succession. This case demonstrates an unusual cause of perilymph fistula diagnosed on imaging and confirmed surgically. He had failed the Newborn Hearing Screening Programme and was therefore referred to audiology, who confirmed profound sensorineural hearing loss in the right ear. MRI showed incomplete partitioning (type 1) of the right cochlea, suggesting cerebrospinal fluid (CSF) leak from the region of the stapes. Exploratory tympanotomy confirmed this, and proceeded to CSF leak repair, obliteration of the Eustachian tube, subtotal petrosectomy, abdominal fat grafting and blind sac closure. Although middle ear effusions are common; particularly in children with recent URTI, the possibility of otogenic CSF leak needs to be considered, especially in cases of recurrent meningitis.

High-Resolution Computed Tomography of the Inner Ear: Effect of Otosclerosis on Cochlear Aqueduct Dimensions.

OBJECTIVES: The cochlear aqueduct is a bony duct connecting the scala tympani with the subarachnoid space. Given the pathophysiology of otosclerosis, including bone resorption and new bone deposition, we hypothesize that the cochlear aqueduct in otosclerotic ears is narrowed. METHODS: A retrospective review of patients with otosclerosis who have undergone high-resolution computed tomography (HRCT) of the temporal bone was completed. The control cohort included 20 patients with the diagnosis of noise-induced hearing loss, without the diagnosis of otosclerosis. Uniform measurements of cochlear aqueduct dimensions were performed using the axial plane. RESULTS: The otosclerosis cohort included 25 males and 52 females with mean age of 52.2 ± 17.6 years. The control group included 10 males and 10 females with mean age of 64.0 ± 18.5 years. The mean cochlear aqueduct length, width mid canal, aperture base, aperture widest diameter, and funnel diameter in millimeters were 12.19 ± 1.66, 0.68 ± 0.28, 4.21 ± 1.67, 3.23 ± 1.47, and 2.70 ± 1.05 in the ears with otosclerotic foci and 11.57 ± 1.66, 0.69 ± 0.29, 2.56 ± 1.59, 2.77 ± 1.67, and 2.58 ± 1.03 in control group, respectively. Statistical difference was seen in length of cochlear aqueduct, aperture base, and aperture widest diameters (P = .017, <.001, .007). CONCLUSIONS: The length of the cochlear aqueduct and the funnel width are statistically longer in the otosclerotic population compared to control. The width of the cochlear aqueduct is not statistically different.

Anatomical Variations in Patients with Ménière Disease: A Tomography Study

Abstract Introduction The etiology of Ménière disease (MD), a difficult-to-treat condition with great morbidity, remains controversial in the literature. The possible clinical and diagnostic impact of anatomical variations of the temporal bone among patients with MD has been recently studied. Objective To identify anatomical variations of the temporal bone associated with the diagnosis of MD. Methods Thirty-seven patients were included, although each ear was considered separately (n = 74). A case group (nA = 33) was composed of the affected ears of patients with definiteMDand a control group (nB = 41) was used consisting of the ears of individuals who did not meet the criteria for MD and of the contralateral ears from patients with unilateral disease. Tomographic images from the individuals included in the study were submitted to a blinded and systematic evaluation regarding a broad variety of anatomical variations of the temporal bone. Obtained data were compared statistically between the groups and after stratifying the study sample. Significance level was set at 0.05. Results Among the affected ears, it was observed an increased number of tomographic scans in which the vestibular aqueduct could not be identified (p = 0.01, Fisher exact test). No statistically significant differences were observed when comparing the affected and contralateral ears frompatients with unilateral MD, between affected ears from patients with unilateral and bilateral disease or between contralateral ears of patients with unilateral affection and patients without the disease. Conclusion Some anatomical variations might be more frequent in the affected ears of patients with MD, such as the lower rates of individualization of the vestibular aqueduct.

The Human Cochlear Aqueduct and Accessory Canals: a Micro-CT Analysis Using a 3D Reconstruction Paradigm.

OBJECTIVE: We sought to study the anatomic variations of the cochlear aqueduct and its accessory canals in human temporal bones using micro-CT and a 3D reconstruction paradigm. More knowledge about the anatomic variations of these structures, particularly at the basal turn of the cochlea and round window niche, may be important to better preserve residual hearing as well as the neural supply during cochlear implant surgery. METHODS: An archival collection of 30 human temporal bones underwent micro-CT and 3D reconstruction. A surface enhancement paradigm was applied. The application displays reconstructed slices as a 3D object with realistic 3D visualization of scanned objects. Virtual sectioning or "cropping" of the petrous bone presented subsequent areas. Thereby, the bony canals could be followed from inside the basal turn of cochlea and middle ear to the jugular foramen. RESULTS: The cochlear aqueduct was always paralleled by an accessory canal containing the inferior cochlear vein. It ran from the basal turn of the cochlea and exited laterally in the jugular foramen. In 70% of the cases, a secondary accessory canal was observed and it derived mostly from a depression or infundibulum located in the floor of the round window niche. This canal also exited in the jugular foramen. The secondary accessory canal occasionally anastomosed with the primary accessory canal suggesting that it contains a vein that drains middle ear blood to the cranial sinus. CONCLUSION: Micro-CT with 3D surface reconstruction paradigm offers new possibilities to study the topographic anatomy of minor details in the human inner ear. The technique creates simulated transparent "castings" of the labyrinth with a coinciding surface view through enhancement of contrast between boundaries. Accessory canals that drain blood from the cochlea, spiral ganglion, and middle ear could be characterized three-dimensionally.

Sneezing and Perilymphatic Fistula of the Round Window: Case Report and Systematic Review of the Literature.

The goal of the present study was to describe a case of perilymphatic fistula (PLF) of the round window (RW) that occurred after sneezing, along with a review of the literature. We report a case of PLF of RW, which was provoked by sneezing, and its consequent medical and surgical treatments. With respect to the review of the literature, articles were initially selected based on their titles or abstracts, followed by methodological evaluation. The patient underwent an explorative tympanotomy (ET) with packaging of RW with the pericondrium, following which the patient's complaints regarding vertigo and imbalance disappeared, but the severe sensorineural hearing loss persisted. For the literature review, five references were selected. These studies showed a great variety in the clinical presentation and healing of symptoms. Sneezing represents a rare but well-recognized cause of PLF, as reported in our case. The correct selection of patients who should undergo ET and an early surgical repair of PLF are mandatory for better outcomes, especially in case of hearing.

Micro-CT study of the human cochlear aqueduct.

OBJECTIVE: The anatomic structure of the cochlear aqueduct (CA) in human temporal bone specimens was observed using micro-computed tomography (CT). MATERIALS AND METHODS: Micro-CT scanning of 18-µm-thick slices was performed on 30 slides of human temporal bone specimens to observe the CA structure and its relationship with its surroundings. The length, internal and external apertures, and the narrowest width of the CA were measured. The differences in CAs were compared between high jugular bulb (HJB) specimens and normal specimens. RESULTS: A large number of CA images were acquired using Micro-CT scanning, which clearly displayed the basic anatomic structures, stereotactic localizations, and adjacent relationships of the CAs. The whole course of a CA was 12.31 ± 3.60 mm, the diameter of the internal aperture was 465 ± 242 µm, the diameter of the external aperture was 2.88 ± 1.06 mm, the narrowest diameter was 601 ± 335 µm, the diameter of the opening of inferior cochlear vein (ICV) was 151 ± 50 µm, the distance between the internal aperture and ICV was 270 ± 197 µm, and the distance between the inferior margin of the internal acoustic meatus (IAM) and the top most part of the external aperture of the CA was 6.783 ± 2.15 mm. No bony obstruction of the CA or CA enlargement was observed in the specimens. A total of 28 CAs had one accompanying bony canal in the surroundings. The length and travelling of the CA were not affected by the level of the jugular bulb (JB). The variation of the travelling of the ICV was larger than that of the CA. CONCLUSION: Micro-CT adequately displayed the bony CA canal and provided a new method for anatomical studies of the CA and a basis for functional studies.

Improved HYDROPS: Imaging of Endolymphatic Hydrops after Intravenous Administration of Gadolinium.

To improve the imaging protocol for the evaluation of endolymphatic hydrops after intravenous administration of a gadolinium-based contrast agent, we modified our previously reported hybrid of reversed image of positive endolymph signal and native image of positive perilymph signal (HYDROPS) method. Although the scan time of the new protocol was half that of the previous one, there were no significant differences between two protocols in the mean contrast noise ratio between the endolymph and perilymph and the area ratio of the endolymph size values in nine patients.

Diameter of the Medial Side of the Cochlear Aqueduct Is Narrower in Meniere's Disease: A Radiologic Analysis.

OBJECTIVE: This study aimed to measure the radiological dimensions of the cochlear aqueduct in Meniere's disease and in low-frequency hearing loss (LFHL) patients and control patients. MATERIALS AND METHODS: Groups of 26 patients (32 ears, including 6 with bilateral involvement) with Meniere's disease, 14 patients (18 ears) with LFHL, and 23 patients with unilateral chronic otitis media, as controls, were enrolled. For the measurements, high-resolution computed tomography (HRCT) of the temporal bone was performed. The cochlear aqueduct was evaluated for the following six parameters: medial opening (MO), petrous apex (PA), otic capsule (OC), lateral opening (LO), distance of the cochlear aqueduct (DC), and length of the cochlear aqueduct (LC). RESULTS: The PA, OC, DC, and LC were not significantly different between the groups. LO could not be measured because the LO was not visible in all cases. The MO diameter was narrower in the Meniere's disease group than in the LFHL group (p=0.001) and in the controls (p=0.035). When the dimensions of both ears were measured in patients with unilateral Meniere's disease, no statistically significant difference was found. CONCLUSION: Compared to LFHL and controls, the MO of the cochlear aqueduct was significantly smaller in the Meniere's disease group.

Comparison of Endolymphatic Duct Dimensions and Jugular Bulb Abnormalities Between Meniere Disease and a Normal Population.

BACKGROUND: The pathogenesis of Meniere disease (MD) has not been fully understood. According to the widely accepted theory, imbalances due to overproduction and/or impaired absorption of endolymph may cause endolymphatic hydrops, which is the hallmark pathological finding in MD. Some developmental temporal bone abnormalities may impair endolymph circulation and absorption, and these abnormalities could be a part of MD pathophysiology. However, structural features of the temporal bone cannot explain MD pathophysiology definitively. The authors aimed to determine the length and width of the endolymphatic duct (ED) along with jugular bulb (JB) abnormalities in MD patients and normal controls using high-resolution computed tomography, and to discuss the results supporting and opposing endolymphatic hydrops based on the data obtained. METHODS: Thirty-six ears of 18 patients with unilateral MD and 34 ears of 17 normal subjects were enrolled. Jugular bulb abnormalities and ED dimensions were evaluated in 3 groups: affected and unaffected ears of MD patients, and healthy controls. The ED dimensions and JB abnormalities were evaluated with high-resolution computed tomography. RESULTS: The ED was found to be significantly shorter and narrower in the affected ears of the MD patients than in the healthy control group. In addition, more JB abnormalities were detected in the affected ears of the MD patients than in the healthy control group. However, there was no difference between the affected and unaffected ears of the MD patients. CONCLUSION: Structural ED abnormalities and JB abnormalities may be predisposing factors for the development of Meniere disease, but cannot fully explain MD pathophysiology.

X-ray microtomography study of otic capsule deficiencies: three-dimensional modelling of the fissula ante fenestram.

BACKGROUND: The postulated sites of perilymph fistulae involve otic capsule deficiencies, in particular, at the fissula ante fenestram. Histological studies have revealed this to be a channel extending from the middle ear, and becoming continuous with the inner ear medial to the anterior limit of the oval window. The relationship between a patent fissula and symptoms of perilymph fistula is contentious. OBJECTIVE: The understanding of the anatomy of the fissula ante fenestram is incomplete. Histopathology is inherently destructive to the delicate ultrastructure of the middle and inner ear. Conversely, X-ray microtomography allows non-destructive examination of the otic capsule. In this study, we used X-ray microtomography to characterise the fissula ante fenestram. MATERIALS AND METHODS: We imaged cadaveric temporal bones with X-ray microtomography. We used the Avizo Fire (Visualization Science Group, Merignac Cedex, France) software to perform post-processing and image analysis. RESULTS: Three-dimensional modelling of the fissula ante fenestram allowed stratification into four forms: rudimentary pit; partial fissula; complete occluded fissula; and complete patent fissula. CONCLUSION: X-ray microtomography showed that the fissula ante fenestram is present in various forms from rudimentary pit to complete deficiency of the otic capsule. This understanding may have implications for otologic surgery and clinical diagnosis of perilymph fistula.

Jugular bulb abnormalities in patients with Meniere's disease using high-resolution computed tomography.

Temporal bone abnormalities such as hypoplasia of the vestibular aqueduct or hypopneumatization of the mastoid have been described in Meniere's disease (MD). Jugular bulb abnormalities (JBA) are one of the most common temporal bone abnormalities. The aim of this study was to evaluate the frequency of JBA in MD. Radiological data obtained by temporal bone high-resolution computed tomography of 200 ears of 167 MD patients (MD group) and 218 ears of 109 patients with normal inner ear function (control group) were analyzed retrospectively. The frequencies of high jugular bulb (HJB), jugular bulb diverticulum (JBD), inner ear adjacent jugular bulb (IAJB) and jugular bulb related inner ear dehiscence (JBID) were evaluated and compared between MD group and control group. IAJB was differentiated into vestibular aqueduct adjacent jugular bulb (VAAJB), cochlear aqueduct adjacent jugular bulb and posterior semicircular canal adjacent jugular bulb. JBID was further analyzed by differentiating into jugular bulb related vestibular aqueduct dehiscence (JBVAD), jugular bulb related cochlear aqueduct dehiscence and jugular bulb related posterior semicircular canal dehiscence. The frequencies of HJB, JBD and IAJB were higher in MD group compared to control group (21, 13.3 %, p = 0.036; 8.5, 3.7 %, p = 0.037; 13.5, 4.6 %, p = 0.001). No differences between both groups were seen in JBID (4.0, 2.3 %, p = 0.315). Most IAJB and JBID were seen in VAAJB and JBVAD. There is a higher frequency of JBA in patients with MD than in patients without inner ear symptoms. Temporal bones of MD patients might be constituted anatomically different, carrying predisposing factors for the development of clinically apparent MD.

High jugular bulb in a cohort of patients with definite Ménière's disease.

OBJECTIVE: To determine the incidence of high jugular bulb in a group of patients with definite Ménière's disease, and to investigate whether the position or size of the jugular bulb is significantly different in the affected ear than in the unaffected ear. METHODS: Retrospective review of patient charts, audiograms, and computed tomography scans to determine the position and size of the jugular bulb in the affected and contralateral ears, as well as other abnormalities. RESULTS: High jugular bulb was found in 57.1 per cent of affected ears. Encroachment of the cochlear and vestibular aqueducts was apparent in 39.3 per cent and 35.7 per cent, respectively, of affected ears. Diverticulum and dehiscence were observed in 28.6 per cent of affected ears. High jugular bulb was significantly associated with encroachment of the cochlear aqueduct (p = 0.003). CONCLUSION: The mediolateral and anteroposterior position of the jugular bulb determines encroachment of the surrounding structures. An abnormal position is postulated to contribute to the development of Ménière's disease.

Radiological findings of the cochlear aqueduct in patients with Meniere's disease using high-resolution CT and high-resolution MRI.

The objective of the present study was to evaluate the cochlear aqueduct (CA) in Meniere's disease (MD) and to disclose radiological differences of CA between MD and non-MD patients by means of high-resolution computed tomography (HRCT) and high-resolution magnetic resonance imaging (HRMRI). Radiological data of 86 ears of MD patients which were separated into 52 ears of diseased side group (MD-D group) and 34 ears of contralateral non-affected side group of unilateral MD (MD-ND group), 27 ears of patients with sensorineural hearing loss (SNHL group) and 56 ears of patients with somatoform dizziness and normal hearing (control group) were analyzed retrospectively. The bony type of CA, the bony length of CA, and the bony width of CA medial orifice was measured in HRCT. The visibility of CA in HRMRI was scored. Fluid length in CA and fluid width in medial orifice were measured in HRMRI. Data were compared between MD-D, MD-ND, SNHL, and control group. There were no significant differences in the bony type of CA, bony length of CA, bony width of CA medial orifice, and fluid width of CA medial orifice between MD-D, MD-ND, SNHL and control group (p > 0.05). However, CA fluid length of MD-D (5.13 ± 1.88 mm) and of MD-ND group (5.44 ± 1.81 mm) was significantly shorter than fluid length of SNHL (6.90 ± 1.55 mm) (p < 0.001, p = 0.001) and of control group (7.43 ± 1.24 mm) (p < 0.001, p < 0.001). The ratio between CA fluid length and CA bony length was the smallest in MD-D group (0.403; p = 0.009). CA bony dimensions of affected ears of MD are normal, but CA fluid length is decreased.

Enlarged cochlear aqueducts: a potential route for CSF gushers in patients with enlarged vestibular aqueducts.

OBJECTIVE: We investigated whether the size of the cochlear aqueduct (CA) is increased in patients with enlarged vestibular aqueducts (EVAs) compared with individuals with normal inner ear anatomy. Furthermore, we assessed whether the size of the CA is related to the cerebrospinal fluid (CSF) gusher during cochlear implantation (CI) surgery. STUDY DESIGN: Retrospective study. SETTING: Tertiary referral center. PATIENTS: The medical records for 35 patients with a biallelic SLC26A4 mutation were reviewed. All of the patients were confirmed to have EVA by temporal bone computed tomography (TBCT) and biallelic SLC26A4 mutation by genetic analysis. Thirty-six age- and sex-matched patients without a mutation in the SLC26A4 gene were selected as comparison group. MAIN OUTCOME MEASURES: The diameters of the CA and vestibular aqueduct (VA) were measured, and the type of CA was evaluated using TBCT. RESULTS: The CA was larger in patients with EVA (2.39 ± 0.99 mm) as compared with controls (1.76 ± 0.87 mm; p < 0.001). The types that could be most easily visualized from the subarachnoid space to the cochlea were more common in patients with EVA. Furthermore, mean CA size was significantly larger in EVA patients with CSF gushers (3.65 ± 1.12 mm) as compared with those without CSF gushers (2.03 ± 0.66 mm; p < 0.001). CONCLUSION: The CA is a potential pathway for CSF gushers between the subarachnoid space and the inner ear. Therefore, we suggest that evaluation of the CA by TBCT may be helpful in predicting intraoperative CSF gushers in patients with EVA.

Enlargement of the cochlear aqueduct: does it exist?

Our intention was to evaluate whether enlargement of the cochlear aqueduct could play a role in dysfunctions of the inner ear. There is little literature dealing with the question of cochlear aqueduct (CA) enlargement and results of reported radiological examinations are contradictory. Therefore, we decided to analyse 400 high-resolution CT-scans of the temporal bone to examine the diameter of the CA. We used scan-data from a 64-line multislice spiral-CT-scanner stored in our PACS-System. CA-enlargement was defined as a diameter of more than 1 mm in the whole otic capsule portion. A classification with four types of CA's proposed by Migirov and Kronenberg in 2005 was applied. Statistical analysis of diameters, different CA-types and side asymmetry was performed. We did not find any CA exceeding 1 mm in diameter in the otic capsule portion, there is no evidence of CA-enlargement, not even in patients with inner ear malformation. A new aspect compared with published literature to date is that nearly in all cases CA was identified, but in different degrees. According to our findings, it seems to be very unlikely that CA-enlargement is a reason for pathologic inner ear condition as it is in case of large vestibular aqueduct.

Communication routes between intracranial spaces and inner ear: function, pathophysiologic importance and relations with inner ear diseases.

OBJECTIVE: There exist 3 communication routes between the intracranial space and the inner ear, the vestibular aqueduct, the cochlear aqueduct, and the internal auditory canal. They possess a key role in inner ear pressure regulation and fluid homeostasis and are related to inner ear diseases. REVIEW METHODS: Relevant literature was reviewed, and the current knowledge of the anatomy, physiologic importance, and relations to inner ear diseases were described. Pathologic communication routes such as semicircular canal dehiscence syndrome were highlighted as well. CONCLUSION: Abnormalities in all 3 communication routes may predispose or be the cause of distinct inner ear pathologic condition and involved in other cochlear and vestibular syndromes, in which their role is not completely clear. The increasing knowledge of the underlying mechanisms encourages promising approaches for possible intervention in the future.

Petromastoid canal and cochlear aqueduct in cochlear implant candidates.

OBJECTIVE: To present temporal bone fine channels in cochlear implantation candidates. METHODS: Review of the axial sections of 108 temporal bone CTs. In type I, the petromastoid canal (PMC) was invisible but appeared as channels in type II and type III, <0.5 and 0.5-1 mm wide, respectively, and in type IV was >1 mm wide. The cochlear aqueduct (CA) was visualized up to the vestibule in type 1, the medial two thirds in type 2, the external aperture and/or the medial third in type 3, and was undetectable in type 4. RESULTS: The PMC size and shape differed significantly between the young (aged <5 years) and older (aged 5-16 years) children and between the young children and adults. A wide PMC (>2 mm) was found in only children younger than 2 years. Children up to 2 years of age and those aged 2 to 5 years demonstrated similar findings. The CA types differed among the pediatric and adult CI candidates, with the main difference appearing after the age of 16 years. There was no correlation between CA and PMC types. CONCLUSIONS: It is likely that the age-related changes in CA and PMC are attributable to the developmental or age-related changes in skull base growth.

Radiology of the cochlear aqueduct.

OBJECTIVES: We sought to determine normative data for the radiologic presentation of the cochlear aqueduct (CA), hypothesizing that increasing the scanner's resolution could enhance detection capability. METHODS: Axial sections of 502 high-resolution computed tomography (CT) images of temporal bones (488 patients) were reviewed. A type 1 CA was visualized on CT scans up to the vestibule, and its portion in the otic capsule segment could be seen as a thin (<1 mm) streak. In type 2, we were able to detect the medial two thirds of the structure, but we failed to see the whole otic capsule portion. In type 3, only the external aperture of the aqueduct and/or the medial third was seen. We defined undetectable CAs as type 4. RESULTS: We obtained CT scans with 0.6-, 1.1-, or 1.3-mm-thick slices through the petrous bones in 9.5%, 58.8%, and 31.7% of cases, respectively. The CA was visible and bilaterally symmetric in 49% of the images, and type 2 was the most commonly detected CA type (36%). The CA was invisible on either side in 21.9% of scans, irrespective of CT resolution, and was asymmetric in 53 of the 502 images. The CA types varied with changes in resolution, although type 3 appeared unchanged independent of alterations in resolution in most cases. CONCLUSIONS: There was no significant difference in CT detection capability between CA types at different resolutions. Computed tomography failed to demonstrate any CAs > or =1 mm in width in the otic capsule segment.