Normal Internal Auditory Canal Research Articles

Symptom: Unilateral Hearing Loss

Symptom: Unilateral Hearing Loss

A case report of vestibular dysfunction caused by cochleovestibular nerve deficiency in a patient with a normal internal auditory canal size

A case report of vestibular dysfunction caused by cochleovestibular nerve deficiency in a patient with a normal internal auditory canal size

The Normal Adult Human Internal Auditory Canal: A Volumetric Multidetector Computed Tomography Study

The purpose of this study was to demonstrate that volumetric analysis of multidetector computed tomography (CT) images can be used to calculate the volume of the adult human internal auditory canal (IAC) reproducibly, and to describe the range of normal IAC volumes in the adult population with subgroup analysis of sex, age, and laterality. Previous studies of the IAC have typically used measurements in two dimensions or by using casts of cadavers to measure IAC volumes. This study is the first to report the normal ranges of IAC volumes measured by CT. Two hundred eighty-one CT scans were assessed. Of the CT scans that met the inclusion criteria, a software package was used to manually contour the IACs in each subject to calculate the volumes in cubic millimeters. Subgroup analysis of laterality, sex, and age was evaluated. Interobserver agreement was calculated for the first 59 patients (118 canals). Two hundred fifty-nine scans (518 canals) met the inclusion criteria. The volumes ranged from 74 to 502 mm, with no statistically significant difference between left and right (p value = 0.69). In males, the range of volumes measured 74 to 502 mm while in females it ranged from 78 to 416 mm. Males had larger IAC volumes than females (Wilcoxon rank-sum test: S = 14,845.0, p value = 0.01 on the right, and S = 14,646, p value = 0.004 on the left). No correlation was found with age (Spearman: -0.10, p value = 0.09 on the right and -0.04, p value = 0.50 on the left). Excellent interobserver agreement was found. IAC volumes of normal adult subjects, measured by CT, were larger in males and not significantly different with respect to age or laterality.

Nontumorous Enlargement of the Internal Auditory Canal: A Risk Factor for Sensorineural Hearing Loss? AHigh Resolution CT-Study.

First aim of the study was to define normal shape and diameter of the internal auditory canal (IAC). In the second part the clinical relevance of IAC-enlargement was analyzed, considering also lesions of the subtle structures at the fundus of the internal auditory canal. 440 high resolution CT-scans of the temporal bone were used for retrospective analysis of the internal auditory canal and its fundus region. The mean value of the IAC diameter in axial and coronal plane was determined. In 20 of 440 patients IAC enlargement was found. In the group with pronounced enlargement (3fold SD) nearly all patients suffered from hearing impairment. In some of them we found structural abnormalities near the IAC fundus in the CSF/perilymph border zone. A new CT-based definition of normal shape and diameter of the internal auditory canal is presented. There is some evidence that a pathologic transmission of CSF-pressure in case of IAC-enlargement and/or abnormal fistulous communications could play an important role in the pathophysilogy of hearing loss. • New CT-based definition of normal internal auditory canal.• Nearly all patients showing pronounced IAC-enlargement suffer from hearing impairment.• Possible pathomechanism: Transmission of CSF-pressure on the inner ear.

Steady‐State Free Precession MRI Imaging as a Screening Evaluation for Vestibular Schwannoma

Objectives: (1) Compare noncontrast steady-state free precession (SSFP, also called FIESTA, CISS, and bFFE) magnetic-resonance imaging (MRI) to contrast-enhanced full sequence MRI for initial evaluation of retrocochlear pathology. (2) Assess the sensitivity and specificity of SSFP alone versus complete contrast-enhanced MRI as the gold standard. Methods: Retrospective review of a tertiary care center radiology imaging database from 2006 to present was performed. Based on statistical power analysis, 50 studies with identified vestibular schwannomas and 53 studies with normal internal auditory canal (IAC) findings were included. Four expert reviewers performed blinded, randomized evaluation of non-contrast SSFP sequence and contrast-enhanced MRI studies to evaluate for retrocochlear pathology. MRI reports from the original studies were used as the gold standard. Using XLSTAT™ statistical software, data were analyzed using a 2-sided z-test of one proportion for each reviewer’s sensitivity and specificity against a 95% standard. Inter-reader reliability was determined using kappa analysis. Results: Four reviewers, including 2 neuroradiologists, one neurotologist, and one neurosurgeon had 100% specificity. Average sensitivity was 96% (range, 94-100%). There was no statistically significant difference when each sensitivity and specificity was compared against a 95% standard or in results between reviewers. Tumors eccentric in the IAC or with significant artifact were more likely to not be identified. Conclusions: Noncontrast SSFP sequence MRI may be an effective initial study to perform for evaluation of vestibular schwannomas. Given its shorter duration (5 minutes versus 25 minutes) as well as the noncontrast method, clear advantages exist for this method.

Cochlear Implant Failure due to Cochlear Nerve Deficiency in a Child with Normal Internal Auditory Canal

The cochlear nerve, which propagates electrical signals to the auditory cortex, must function well for successful cochlear implantation. A narrow internal auditory canal (IAC) increases the risk of hypoplasia or aplasia of cochlear nerve, which may result in the failure of cochlear implantation. Therefore, a functioning cochlear nerve must be verified before deciding to do cochlear implantation by means of behavioral audiometry, electrophysiologic tests, or imaging studies in cases with narrow IAC. On the other hand, a candidate with a normal IAC can be overlooked in investigating the presence of functioning cochlear nerve. Because normal IAC does not always guarantee the presence of normal cochlear nerve, the functioning cochlear nerve should be proved prior to cochlear implantation in those cases. We report on a child, who had normal IAC and cochlea but failed auditory stimulation after cochlear implantation, and who was diagnosed as having cochlear nerve deficiency through retrospective review.

S237 – Computerized Tomography in the Prediction of CSF Gusher

Objectives 1) Identify anatomic variations of the temporal bone in children with and without cochlear malformations who experienced an intra-operative cerebrospinal fluid (CSF) gusher at the time of cochlear implantation. 2) Compare the anatomic findings in the current study to those described in prior studies. Methods A retrospective case-controlled chart review was performed on patients undergoing cochlear implant surgery. Computerized tomography images were analyzed in a single-blind fashion for characteristics and measurements of both the right and left cochlea, internal auditory canal, cochlear aperture, facial nerve canal, vestibular aqueduct, cochlear aqueduct, oval window, round window, vestibule, mastoid, tegmen tympani and semi-circular canals. After verifying equal variances, data was statistically evaluated utilizing the paired 2-tailed t test with criterion for statistical significance set at p < 0.05. Results The average age at implantation for this series of children was 4 years old. 70% of patients had cochlear malformations. 25% of patients had an abnormal internal auditory canal (IAC) and 30% had a widened cochlear aperture. Most patients with an abnormal IAC had an abnormal cochlear aperture; however, some patients with a normal IAC also had an abnormal cochlear aperture. Correlations between the temporal bone anatomy and the incidence of CSF gushers will be discussed. Conclusions Specific characteristics of the temporal bone anatomy may lead to an increased incidence of CSF gusher in cochlear implant surgery. Computerized tomography of the temporal bone can assist in the surgeon in evaluation and planning for cochlear implantation.

Internal Auditory Canal Morphology in Children with Cochlear Nerve Deficiency

To describe the internal auditory canal (IAC) and inner ear morphologic characteristics of children with cochlear nerve (CN) deficiency. Retrospective case series. Tertiary referral center. Fourteen children with small or absent (deficient) CNs have been identified by means of high-resolution magnetic resonance imaging (MRI). MRI of the brain. Clinical evaluation. Review of medical records, audiological testing results, and imaging studies. Images were evaluated for the structure of the cochlear, vestibular and facial nerves, IACs and inner ears. Audiometric thresholds were evaluated in all subjects. Fourteen children with small or absent (deficient) CNs have been identified by means of high-resolution MRI. A review of the medical records, audiologic testing results, and imaging studies was undertaken. The images were evaluated for the structure of the cochlear, vestibular and facial nerves, IACs, and inner ears. The audiometric thresholds were evaluated in all subjects. Among the 14 patients, 5 had known syndromes. MRI allowed an exact specification of the nervous structures within all ears with normal-size IACs. Precise characterization of the nerves in ears with small IACs was more difficult, requiring a consideration of both imaging findings and functional parameters. Five children had bilateral deficient CNs, whereas the remaining 9 subjects were affected unilaterally. Thus, 19 ears had CN deficiency (absent CN, 16; small CN, 3). Eleven ears had normal-size IACs and deficient CNs. Of the 9 ears with small IACs, 8 had deficient CNs (absent, 7; small, 1) on the basis of both MRI and functional assessments. Two ears with small IACs had clear morphologic and/or functional evidence for the presence of a CN: one had a small-size CN on MRI, whereas another had a single nerve in a small IAC with present facial and auditory functions. The findings of this study suggest that CN deficiency is not an uncommon cause of congenital hearing loss. The findings that most ears with CN deficiency had normal IAC morphology and that two ears with small IACs had CNs present indicate that IAC morphology is an unreliable surrogate marker of CN integrity. On the basis of these findings, we think that high-resolution MRI, rather than CT imaging, should be performed in all cases of pediatric hearing loss, especially in those cases where profound hearing loss has been documented. For ears with small IACs, the resolution of MRI currently remains limiting. In these cases, the determination of CN status frequently requires a variety of anatomic (CT and MRI) and functional tests (auditory brainstem response, otoacoustic emissions, behavioral audiometry, and physical examination).

A new classification for cochleovestibular malformations.

The report proposes a new classification system for inner ear malformations, based on radiological features of inner ear malformations reviewed in 23 patients. The investigation took the form of a retrospective review of computerized tomography findings relating to the temporal bone in 23 patients (13 male and 10 female patients) with inner ear malformations. The subjects were patients with profound bilateral sensorineural hearing loss who had all had high-resolution computed tomography (CT) with contiguous 1-mm-thick images obtained through the petrous bone in axial sections. The CT results were reviewed for malformations of bony otic capsule under the following subgroups: cochlear, vestibular, semicircular canal, internal auditory canal (IAC), and vestibular and cochlear aqueduct malformations. Cochlear malformations were classified as Michel deformity, common cavity deformity, cochlear aplasia, hypoplastic cochlea, incomplete partition types I (IP-I) and II (IP-II) (Mondini deformity). Incomplete partition type I (cystic cochleovestibular malformation) is defined as a malformation in which the cochlea lacks the entire modiolus and cribriform area, resulting in a cystic appearance, and there is an accompanying large cystic vestibule. In IP-II (the Mondini deformity), there is a cochlea consisting of 1.5 turns (in which the middle and apical turns coalesce to form a cystic apex) accompanied by a dilated vestibule and enlarged vestibular aqueduct. Four patients demonstrated anomalies involving only one inner ear component. All the remaining patients had diseases or conditions affecting more than one inner ear component. Eight ears had IP-I, and 10 patients had IP-II. Ears with IP-I had large cystic vestibules, whereas the amount of dilation was minimal in patients with IP-II. The majority of the semicircular canals (67%) were normal. Semicircular canal aplasia accompanied cases of Michel deformity, cochlear hypoplasia, and common cavity. In 14 ears, the IAC had a defective fundus at the lateral end. In two ears the IAC was absent. In all seven cases of common cavity malformations, there was a bony defect at the lateral end of the IAC. In five of them the IAC was enlarged, whereas in two the IAC was narrow. All patients with IP-I had an enlarged IAC, whereas in patients with type II disease, four had a normal IAC and 10 had an enlarged IAC. All cases of IP-II had an enlarged vestibular aqueduct, whereas this finding was not present in any of the cases of IP-I. In all cases, the vestibular aqueduct findings were symmetrical on both sides (simultaneously normal or enlarged). No patient demonstrated enlargement or any other abnormalities involving the cochlear aqueduct. Radiological findings of congenital malformations in the present study suggested two different types of incomplete partition. Cystic cochleovestibular malformation (IP-I) and the classic Mondini deformity (IP-II). The type I malformation is less differentiated than the type II malformation. Classic Mondini deformity has three components (a cystic apex, dilated vestibule, and large vestibular aqueduct), whereas type I malformation has an empty, cystic cochlea and vestibule without an enlarged vestibular aqueduct. Mondini deformity represents a later malformation, so the amount of dysplasia is much less than in type II. Therefore, it is more accurate and useful for clinical purposes to classify these malformations (in descending order of severity) as follows: Michel deformity, cochlear aplasia, common cavity, IP-I (cystic cochleovestibular malformation), cochlear hypoplasia, and IP-II (Mondini deformity). Only in this way can these complex malformations be grouped precisely and the results of cochlear implantation compared.

CT and MR imaging of intralabyrinthine schwannoma: report of two cases and review of the literature.

Two cases of intralabyrinthine schwannoma were studied with computed tomography (CT) and magnetic resonance (MR) imaging. On CT scans, a soft-tissue mass was identified in the round window niche in both cases. Widening of the basilar turn of the cochlea and characteristic erosion of the promontory were noticed in one case. Preoperative MR imaging (performed in only one case) revealed a soft-tissue mass in the labyrnth, extending into the round window niche. Findings at CT and MR imaging are discussed, and a differential diagnosis is given. The literature is reviewed. The authors' findings suggest that CT and MR imaging may prove very valuable in the previously difficult preoperative diagnosis of these tumors. In the setting of progressive sensorineural hearing loss, atypical Meniere disease, or recurrent vertigo, the presence of a mass in the labyrinth or labyrinthine windows- delineated on CT or MR images, despite a normal internal auditory canal, cerebellopontine angle, or brain stem - is highly suggestive of intralabyrinthine schwannoma.

突発性難聴の形で発症した聴神経腫よう

A 41-year-old woman suddenly noticed hearing loss and tinnitus of the left ear. She did not experience any vertigo. Sudden deafness was suspected, and she was treated with steroid hormone intravenously 4 days after the onset of hearing loss. Audiometric testing revealed a sensorineural deafness with an average of 63 dB. The response to caloric stimulation was normal in both ears. Stenvers view showed no abnormalities. Two weeks after treatment the hearing in her left ear recovered to 26 dB. in pure tone average.Twenty seven months later she consulted an ophthalmologist with a complaint of headache and myodysopsia. Papilledema was noted. CT disclosed masses in the right frontal lobe and left cerebelloportine angle. Stenvers view showed normal internal auditory canal in both ears. Pure tone audiogramas revealed sensorineural hearing loss with an average of 72 dB. in the left ear. Caloric response was absent in both ears. A meningioma in the right frontal lobe and an acoustic neurinoma in the left cerebellopontine angle were removed by neurosurgeons.The authors stress that patients with sudden deafness should be followed after treatment for as long as possible, even if hearing is improved by medical treatment, and that ABR is desirable in the diagnostic evaluation of acoustic neurinoma.

Computed Tomography of Jugular Foramen Neurinomas -

Four jugular foramen neurinomas studied by computed tomography and verified by surgery originated from the glossopharyngeal nerve. Characteristic CT findings were a mixed low and isodense extraaxial mass with ring-like enhancement in the cerebellopontine angle; enlargement of the jugular foramen, with smooth margins and a normal internal auditory canal; and an extracranial soft tissue mass extending through the jugular foramen.

Demonstration of the hypoglossal canal at positive contrast posterior fossa myelography. The fickle finger sign.

HomeRadiologyVol. 102, No. 2 PreviousNext NeuroradiologyDemonstration of the Hypoglossal Canal at Positive Contrast Posterior Fossa MyelographyThe Fickle Finger SignCharles J. Geilfuss, Lucius HeriotCharles J. Geilfuss, Lucius HeriotAuthor Affiliations Department of Radiology Medical University of South CarolinaCharleston, S. C. 29401Charles J. GeilfussLucius HeriotPublished Online:Feb 1 1972https://doi.org/10.1148/102.2.363MoreSectionsPDF ToolsImage ViewerAdd to favoritesCiteTrack CitationsPermissionsReprints ShareShare onFacebookTwitterLinked In AbstractThe hypoglossal canal may occasionally fill with contrast medium during posterior fossa myelography. If the internal auditory canal is blocked by an acoustic neuroma, the contrast filled hypoglossal canal can be mistaken for a normal internal auditory canal. Additional views and/or tomography, which is diagnostic, will prevent this error. A representative case is presented.Article HistoryAccepted: Aug 1971Published in print: Feb 1972 FiguresReferencesRelatedDetailsCited ByThe Laryngoscope, Vol. 94, No. 2Recommended Articles RSNA Education Exhibits RSNA Case Collection Vol. 102, No. 2 Metrics Altmetric Score PDF download

Pontocerebellar cisternography.

Small space-occupying lesions within the pontocerebellar (cerebellopontine-angle) cistern usually can be demonstrated by fractional pneumoencephalography augmented by tomography. Occasionally they are missed entirely or the results are inconclusive; and furthermore, it is impossible to delineate lesions confined to the internal auditory canal. The early diagnosis of lesions in this area is extremely important to the surgeon since lesions, if small, can be removed with a minimal mortality and morbidity rate. The majority of these lesions are benign, and a surgical cure is possible in most patients. The standard technic of Pantopaque cisternography (1–4) requires vertical beam radiographic exposures of the pontocerebellar cistern with the patient prone and the head in an oblique position, which makes recognition of anatomic details of the petrous bone difficult. Moreover, examination of the pontocerebellar cistern in the oblique position results in incomplete filling, which precludes accurate analysis of cisternal anatomy, and, in addition, opacification of the normal internal auditory canal is not guaranteed. When the subarachnoid extension into the internal auditory canal fails to fill, it is frequently impossible to determine whether this is the result of incomplete filling of the cistern to the level of the canal or of a lesion confined to the canal. Incomplete filling of the cistern makes interpretation difficult and the differentiation between tiny lesions and technical artefacts hazardous. This report is a review of our initial experience with a new technic designed to eliminate these shortcomings. Roentgenograms of illustrative cases are presented. Technic and Procedure The technics previously described have been modified to guarantee total filling of the pontocerebellar cistern beyond the level of the internal auditory canal while utilizing standard submentovertex and postero-anterior half-axial projections with the patient in the lateral decubitus position. (a) The patient is placed in a lateral decubitus position, and a harness is attached. Lumbar puncture is performed and 4 to 6 cc of Pantopaque instilled into the subarachnoid space. (b) The head is maintained in the mid-sagittal plane by firm sponges. Under fluoroscopic control the head end of the table is lowered 40 to 50°. As Pantopaque enters the foramen magnum the position of the dependent tonsil is noted. The table is returned to the horizontal as soon as Pantopaque is identified just superior to the petrous pyramids as it starts to enter the interpeduncular cistern (Fig. 1). (c) The head is extended, and a cross-table submentovertex exposure is made using a grid cassette (Fig. 2). The head is then flexed, and a crosstable postero-anterior half-axial exposure is made with the tube angled 30° to the orbitomeatal line (Fig. 3). Insufficient angulation may result in superimposition of the internal auditory canal on the cistern.