Isolated primary unilateral stenosis of the internal auditory canal

Narrow Internal Auditory Canal With Duplication in a Patient With Sensorineural Hearing Loss and Facial Palsy: A Case Report

A narrow internal auditory canal with duplication is a rare congenital disorder of temporal bone. High-resolution CT of the temporal bone is a preferred modality for assessing the bony framework of the temporal bone and inner and middle ear structures and is thus commonly used. Of late, due to rapid advancement in technology, MRI can assess the neural structures, including the vestibulocochlear and facial nerves. Here, we present the case of a 29-year-old male with congenital left-sided sensorineural hearing loss and left-sided facial palsy.

The Role of Computed Tomography in the Diagnosis of Congenital Sensorineural Hearing Loss

Introduction  One of the paths in the investigation of congenital sensorineural hearing loss (CSNHL) is to try to characterize its etiology through the inner ear evaluation using high resolution computer tomography (CT) scans. With minor malformation, it is not always possible for a simple visual inspection to recognize if the structure in the inner ear is normal or not. Objective  To verify if measurements of the inner ear are predictive of sensorineural hearing loss (SNHL) and suggest cutoff points of size limits. Methods  Retrospective cross-sectional study of inner ear CT scan measurements of 214 patients, 50 with congenital SNHL (CSNHL) and 164 acquired SNHL (ASNHL) (control group). Results  In the CSNHL group, central bony island (CBI) were 0.48 mm smaller ( p  < 0.001), cochlear nerve aperture was (CNA) 0.10 mm smaller ( p  < 0.001), and cochlea height was (CH) 0.15 mm smaller ( p  < 0.001). Vestibular aqueduct (VA) and cochlea width (CW) were similar between groups (0.70 vs 0.72, p  = 0.19, and 7.20 vs 7.15 p  = 0.23). The predictive cutoff points for CSNHL were CBI = 3.6 mm, CAN = 1.4 mm, CH = 3.4 mm, CW = 7.0 mm, and VA = 0.9 mm. Conclusion  Congenital sensorineural hearing loss determined a decrease in CBI, opening of the cochlear nerve (OCN), and CW. Thus, these measures, at the cutoff points indicated, should make us aware of the diagnosis of congenital hearing loss.

De novo sensorineural hearing loss sequelae of narrow, duplicated internal auditory canal: Case series and literature review

INTRODUCTION

A narrow duplicated internal auditory canal (IAC) is an extremely rare anomaly, likely associated with congenital sensorineural hearing loss due to aplasia/hypoplasia of the vestibulocochlear nerve or the cochlear branch alone. We aimed to review our experience with IAC duplication, describe its clinical characteristics, and present a literature review.

CASE PRESENTATION

Our Otology database was searched for children who showed duplication of the IAC. Clinical characteristics of two children with bilateral duplication of the IAC are described. Data regarding clinical history, auditory assessment, magnetic resonance imaging (MRI), and computed tomography (CT) were collected and analyzed. The separated, accessory bony canals were demonstrated on high-resolution CT scans, and the nerves were demonstrated on MRI.

DISCUSSION

To date, a few cases of narrow duplicate IAC have been reported in the literature, Approximately 20% of patients with congenital SNHL are found to show inner-ear bony abnormalities on CT, but much uncertainty still exists about the mechanism underlying IAC stenosis.5 Imaging findings of the temporal bone in our case series demonstrated asymmetrical narrowing of both IACs, there is no clear evidence in the literature supporting the predominance of one side over the other. In our series, facial nerve function was intact bilaterally. As for our cases, both patients were enrolled in a single-sided deafness evaluation for a trial of options such as BAHA, CROS, cochlear implants, and other non-implantable hearing aids. Furthermore, addressing the important factors will optimize the outcomes including surgery at early age to optimize neural plasticity, with intense long-term therapy.

CONCLUSION

Congenital duplication of the IAC likely convoying sensorineural hearing loss due to aplasia/hypoplasia of the vestibulocochlear nerve. Early diagnosis and intervention are essential to optimize patient outcomes.

Imaging Evaluation of Pediatric Sensorineural Hearing Loss in Potential Candidates for Cochlear Implantation

Computerized tomography (CT) and magnetic resonance (MR) are complementary in the imaging of the labyrinth, the internal auditory canal and the brain in children with sensorineural hearing loss who are being evaluated for cochlear implantation. An accurate anatomical description of the inner ear is essential in the preoperative work up. Computerized tomography visualizes the bony structures, whereas MR can discern soft-tissue components including intra labyrinthine fluid, cerebrospinal fluid (CSF), nerves, and vessels within the IAC. This prospective study was conducted in the Department of Otorhinolaryngology, Head & Neck Surgery, Government Medical College, Srinagar. 40 children in the age group of 1-16 years with unidentified causes of bilateral SNHL were analysed radiologically over the period of 2 years from Dec 2011 to Jan 2014. Each patient underwent MRI and high resolution CT scanning of temporal bone in axial and coronal planes. Out of the 40 patients 22 were males (55 %) and 18 were females (45 %). 30 patients (72.5 %)in our study had normal radiological scans. Five patients (12.5 %) had B/L large vestibular aqueduct and two patients (5 %) had internal auditory canal stenosis with cochlear nerve hypoplasia on CT and MR imaging. Cochlear dysplasia was present in two patients (5 %) and semicircular canal dysplasia was present in one patient (2.5 %) as an isolated finding on HRCT. In addition isolated cochlear nerve hypoplasia was present in one patient (2.5 %). Hyperintense basal ganglia lesion suggestive of kernicterus was present in one patient (2.5 %) and hyperintense posterior parietal and occipital white matter lesions suggestive of congenital CMV infection was present in one patient (2.5 %) on MR imaging. Arachnoid cysts of middle cranial fossa was an incidental finding present in one patient. Radiological abnormalities of the inner ear are not uncommon. Computerized tomography and MRI are important modalities to analyze the inner ear in children with unexplained SNHL. MRI with an extremely small field of view should be used to study possible abnormalities of the vestibulocochlear nerves.

The cochlear nerve canal and internal auditory canal in children with normal cochlea but cochlear nerve deficiency

BACKGROUND

There is an increasing frequency of requests for cochlear implantation (CI) in deaf children and more detailed image information is necessary for selecting appropriate candidates. Cochlear nerve deficiency (CND) is a contraindication to CI. Magnetic resonance imaging (MRI) has been used to evaluate the integrity of the cochlear nerve. The abnormalities of the cochlear nerve canal (CNC) and internal auditory canal (IAC) have been reported to be associated with CND.

PURPOSE

To correlate CNC manifestation, size, and IAC diameter on high-resolution CT (HRCT) with CND diagnosed by MRI in children.

MATERIAL AND METHODS

HRCT images from 35 sensorineurally deaf children who had normal cochlea but bilateral or unilateral CND diagnosed by MRI were studied retrospectively. The CNC and IAC manifestation and size were assessed and correlated with CND.

RESULTS

CND was diagnosed by MRI in 54/70 ears (77.1%). Thirty-two ears had an absent cochlear nerve (59.3%), while 22 ears had a small cochlear nerve (40.7%). The CNC diameter was <1.5 mm in 36 ears (66.7%). The CNC diameter ranged between 1.5 and 2.0 mm in seven ears (13.0%) and was >2.0 mm in 11 ears (20.4%). The IAC diameter was <3.0 mm in 25 ears (46.3%) and >3.0 mm in 29 ears (53.7%).

CONCLUSION

The hypoplastic CNC might be more highly indicative of CND than that of a narrow IAC.

Duplicate internal auditory canals with facial and vestibulocochlear nerve dysfunction

Objective:

We report an extremely rare case of duplication of the internal auditory canal associated with dysfunction of both the facial and vestibulocochlear nerves. We also review the literature regarding the integrity of the facial and vestibulocochlear nerves in such cases.

Case report:

A 34-year-old man presented with unilateral, right-sided, sensorineural hearing loss and facial nerve palsy since childhood. Facial nerve function was observed to be House–Brackmann grade III. Computed tomography and magnetic resonance imaging demonstrated ipsilateral duplicate, vacant internal auditory canals. Based on the clinical presentation, we interpreted these radiological findings as aplasia of the vestibulocochlear nerve and severe hypoplasia of the facial nerve.

Conclusion:

To our best knowledge, this is the first report of vestibulocochlear nerve aplasia and severe facial nerve hypoplasia in a case of ipsilateral duplication of the internal auditory canal. High resolution gradient echo magnetic resonance imaging sequences are advocated for assessment of neural integrity in patients with an abnormal internal auditory canal and facial and/or vestibulocochlear nerve dysfunction.

Histopathologic investigation of the dimensions of the cochlear nerve canal in normal temporal bones

OBJECTIVE

Establish normative histopathologic data on the dimensions of the cochlear nerve canal (CNC).

BACKGROUND

Evidence suggests that when the CNC is stenotic, the cochlear nerve may be hypoplastic. There is clear agreement in the literature that an internal auditory canal less than 2 mm in diameter is a relative contraindication to cochlear implantation in children. However, there has only been recent recognition in research that a narrowed CNC may lead to diminished ability to interpolate and use auditory information delivered through a cochlear implant. However, there is no consensus in the literature on the normal diameter of the CNC and what parameters should be used to determine stenosis. In addition, no normative histopathologic data is available for CNCs.

METHODS

This study evaluated histopathologic axial sections from normal human temporal bones to measure the cochlear nerve canal in 110 individuals, aged 0-100 years. The maximum CNC diameter in each normal patient was identified and measured.

RESULTS

The mean CNC diameter was 2.26 mm with a standard deviation of 0.25 mm. There were no differences in the CNC diameters between males and females or with increasing age.

CONCLUSION

These measurements should provide a normative reference for comparison in histopathologic and radiographic assessment of any patient with suspected cochlear nerve canal stenosis.

Computed Tomography measurements of the normal and the pathologic cochlea in children

BACKGROUND

Radiological investigation is frequently undertaken to assess the aetiology of sensorineural hearing loss (SNHL).

OBJECTIVE

To establish the CT measurements of the normal cochlea in children and to determine radiological criteria correlated with SNHL.

MATERIALS AND METHODS

A retrospective study of temporal bone CT performed in 159 children, age range from 3 days to 16 years between February 1999 and July 2004. A control group (n = 88) comprised children without SNHL; the SNHL group comprised 71 children. The width of the second turn of the cochlea (CW), the cochlear height (CH), and the width of the bony canal for the cochlear nerve (WCN) were measured on a reference plane containing the modiolus, the posterior semicircular canal, the footplate, and the stapes arch.

RESULTS

Width of the canal measurements <or=1.7 mm or >or=2.5 mm supported the diagnosis of SNHL with a specificity of 97% and 91%, respectively. Cochlear width was found to be significantly smaller in the SNHL group (5.61 +/- 0.51 mm) than in the control group (5.75 +/- 0.31 mm, P < 0.02), a size <5.4 mm being highly suggestive of SNHL with a specificity of 90%. No significant variations of all measurements were found with age.

CONCLUSION

Appropriate measurements of WCN and CW are highly correlated with SNHL.

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.

Bilateral duplication of the internal auditory canal

Duplication of the internal auditory canal is an extremely rare temporal bone anomaly that is believed to result from aplasia or hypoplasia of the vestibulocochlear nerve. We report bilateral duplication of the internal auditory canal in a 28-month-old boy with developmental delay and sensorineural hearing loss.

Internal auditory canal stenosis in congenital sensorineural hearing loss

OBJECTIVE

Sensorineural hearing loss (SNHL) due to internal auditory canal (IAC) stenosis with hypoplasia of the cochleovestibular nerve is a rare disorder. The diagnosis of the IAC stenosis requires both high resolution computed tomography scan (HRCT) and magnetic resonance imaging (MRI).

METHODS

A retrospective review over 6 years in an academic tertiary referral center was performed.

RESULTS

Six patients with congenital SNHL were diagnosed with congenital IAC stenosis. Four had unilateral and two had bilateral IAC stenosis after imaging. MRI showed hypoplastic vestibulocochlear nerve in all cases.

CONCLUSIONS

This paper highlights the importance of imaging in diagnosing IAC stenosis and detecting the presence of cochleovestibular nerve in cases of congenital SNHL.

Narrow duplicated internal auditory canal: radiological findings and review of the literature

Narrow duplicated internal auditory canal (IAC) is a rare malformation of the temporal bone that is associated with ipsilateral congenital sensorineural hearing loss. This may be an isolated finding or a part of a syndrome. Radiological examination should demonstrate aplasia or hypoplasia of the neural components of the narrow IAC, to guide the surgical approach. We report a 7-year-old boy with Klippel-Feil syndrome with a narrow double IAC with no sensorineural hearing loss but with conductive hearing loss. In this patient, the IAC consisted of two separate narrow bony canals clearly seen on 3D temporal bone CT and one nerve that was delineated on MRI. The contralateral external auditory canal was stenotic and the ossicles were dysplastic.

Narrow, duplicated internal auditory canal

A narrow internal auditory canal (IAC) constitutes a relative contraindication to cochlear implantation because it is associated with aplasia or hypoplasia of the vestibulocochlear nerve or its cochlear branch. We report an unusual case of a narrow, duplicated IAC, divided by a bony septum into a superior relatively large portion and an inferior stenotic portion, in which we could identify only the facial nerve. This case adds support to the association between a narrow IAC and aplasia or hypoplasia of the vestibulocochlear nerve. The normal facial nerve argues against the hypothesis that the narrow IAC is the result of a primary bony defect which inhibits the growth of the vestibulocochlear nerve.

Evaluation of the internal auditory canal with virtual endoscopy

OBJECTIVE

Three-dimensional imaging can improve the understanding and comprehension of complex anatomy. Recent advances in software development allow the construction of a virtual endoscopic view of anatomic structures. This report applies virtual endoscopic capabilities to imaging of the internal auditory canal.

STUDY DESIGN, SETTING, AND PATIENTS

We conducted a retrospective case review at a tertiary referral center of patients with abnormal internal auditory canal anatomy on computed tomography.

INTERVENTIONS

Computed tomography images were obtained using conventional clinical algorithms involving multiple, 1-mm-thick slices through the temporal bone. Three-dimensional reconstructions were made using General Electric Advantage Windows Navigator software. The virtual endoscopic image-processing algorithm used selected image intensity threshold levels to visualize internal auditory canal anatomy from an endoscopic perspective.

RESULTS

Eleven cases of abnormalities of the internal auditory canal were retrospectively identified. Clinical applications using the virtual endoscopic images are presented. The virtual endoscopic images supported prior clinical decision making in 6 of the 11 cases evaluated.

CONCLUSION

This technique shows promise for the diagnosis, surgical planning, and teaching of temporal bone anatomy. Usefulness is dependent on acquisition parameters and clinical indications for examination.

Cochlear implantation for auditory rehabilitation in Camurati-Engelmann disease

Camurati-Engelmann disease (progressive hereditary diaphyseal dysplasia) is a rare sclerotic bone disease involving the diaphyses of the long bones, skull base, and clavicles. Progressive sclerosis of cranial nerve foramina has been implicated in cranial nerve deficits. including facial nerve palsy, vestibular disturbances, and hearing loss. Two patients with Camurati-Engelmann disease and concomitant sensorineural hearing loss are presented. Both patients were evaluated for cochlear implantation. One patient was successfully implanted after preoperative imaging revealed no involvement of the internal auditory canals. The porous nature of the affected bone, however. necessitated the inactivation of 1 electrode to prevent facial nerve stimulation. A second patient was rejected as a potential implant recipient due, in part, to narrow internal auditory canals and rapidly progressive disease. The otologic manifestations of Camurati-Engelmann disease are reviewed, and issues related to cochlear implantation in this rare disease are discussed.