Radiology of the Cochlear Aqueduct

Cochlear Aqueduct Morphology in Superior Canal Dehiscence Syndrome

The cochlear aqueduct (CA) connects the scala tympani to the subarachnoid space and is thought to assist in pressure regulation of perilymph in normal ears, however, its role and variation in inner ear pathology, such as in superior canal dehiscence syndrome (SCDS), is unknown. This retrospective radiographic investigation compared CA measurements and classification, as measured on flat-panel computerized tomography, among three groups of ears: controls, n = 64; anatomic superior canal dehiscence without symptoms (SCD), n = 28; and SCDS, n = 64. We found that in a multinomial logistic regression adjusted for age, sex, and BMI, an increase in CA length by 1 mm was associated with a lower odds for being in the SCDS group vs. control (Odds ratio 0.760 p = 0.005). Hierarchical clustering of continuous CA measures revealed a cluster with small CAs and a cluster with large CAs. Another multinomial logistic regression adjusted for the aforementioned clinical covariates showed an odds ratio of 2.97 for SCDS in the small CA cluster as compared to the large (p = 0.004). Further, no significant association was observed between SCDS symptomatology-vestibular and/or auditory symptoms-and CA structure in SCDS ears. The findings of this study lend support to the hypothesis that SCDS has a congenital etiology.

Anatomical Variations, Surgical Difficulties, and Complications Associated with Cochlear Implantation in Different Age Groups of the Pediatric Population of Nepal: A Tertiary Level Hospital-Based Study

Pediatric cases account for the major proportion of the population for whom cochlear implantation is indicated. This study aims to review the anatomical variations, surgical difficulties, and complications associated with cochlear implantation surgery in different age groups of the pediatric population of Nepal.This study was conducted at Tribhuvan University Teaching Hospital, Nepal. A prospectively set data of cases who underwent cochlear implantation between January 2015 and March 2020 were analyzed for details of surgical procedure, surgical difficulties, and intraoperative and postoperative complications. The anatomical variations encountered during surgery were classified as: developmental anomalies, round window niche variations and acquired abnormalities resulting from inflammation. Intraoperative surgical difficulties were defined based on the operating surgeon's perspective. Complications following cochlear implantation were classified as surgical and nonsurgical or device-related. We used SPSS version 25 for the analysis of our data. Chi-square test and Fisher's exact test were used to analyze the statistical association.The most commonly encountered difficulty was the requirement of an extended posterior tympanotomy approach due to poor visualization of round window niche. There was a statistically significant association of difficult insertion of electrodes with round window niche visibility. The common complications encountered were intraoperative facial nerve exposure, bleeding, electrode-related problems, cerebrospinal fluid gusher, and device failure.Cochlear implantation with an experienced surgeon in pediatric population is a relatively safe procedure. There is no association of the difficulties and complications related to surgery with the different age groups.

Relationship Between the Cochlear Aqueduct and Internal Auditory Canal: Surgical Implications for Transcanal Transpromontorial Approaches to the Lateral Skull Base

HYPOTHESIS

The cochlear aqueduct (CA) is subject to considerable anatomical variability. We hypothesize a topographical relationship between the CA and the internal auditory canal (IAC).

BACKGROUND

The CA represents the lower limit of dissection during transcanal transpromontorial approaches to the lateral skull base due to its close relationship to the lower cranial nerves and jugular vein.

METHODS

Three-dimensional models from high-resolution computed tomography scans of normal human temporal bones were created using threshold-based segmentation. The CA was classified into four categories. Five points were determined on the three-dimensional models to measure the surgically relevant relationships.

RESULTS

Segmentation was performed on 26 high-resolution computed tomography scans. The average length of the virtual and visual part of the CA was 6.6 mm (SD ±1.7 mm) and 5.5 mm (SD ±1.3 mm) respectively. The mean distance between the IAC and the medial end of the visual part of the CA was 3.8 mm (±0.7 mm), while the average distance between the IAC and the lateral end was 1.4 mm (±0.6 mm). The distance between the visual part of the CA and the IAC increased by 0.25 mm per from the fundus of the IAC.

CONCLUSION

A close relationship between the CA and the IAC could be established, despite the anatomical variability of the CA. The distance between CA and IAC increases by 0.25 per mm from the fundus to the porus of the IAC. These findings quantify the inferior limit of dissection of the transcanal transpromontorial approach to the lateral skull base.

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.

Sensorineural Hearing Loss in the Nonimplanted Ear Following Cochlear Implantation in a Patient With Bilateral Enlarged Vestibular Aqueducts

OBJECTIVE

To document the case of a patient with bilateral enlarged vestibular aqueducts who experienced sensorineural hearing loss in the nonimplanted ear following unilateral cochlear implantation complicated by perilymph gusher requiring lumbar drain insertion and to highlight the need to counsel regarding the risk of potential hearing loss to the contralateral ear when preparing for cochlear implants in the setting of inner ear malformations.

PATIENTS

One patient with bilateral enlarged vestibular aqueducts in a tertiary referral center.

INTERVENTION(S)

Cochlear implantation complicated by perilymph gusher requiring lumbar drain insertion.

MAIN OUTCOME MEASURE(S)

Bone conduction hearing thresholds, word recognition scores.

RESULTS

The patient underwent unilateral cochlear implantation, which was complicated by a perilymphatic gusher and necessitated placement of an intraoperative lumbar drain. On postoperative day 1, the patient reported hearing loss in the opposite ear. The word recognition score in the contralateral ear dropped from 24% at preimplantation to 8% at 2-weeks postimplantation, and did not improve at 6 months postimplantation. Moreover, the bone conduction threshold at 1 kHz worsened from 20 dB preoperatively to no response at 75 dB (the limit of the testing equipment) at 2-weeks postoperatively and only partially improved to 40 dB at 6 months postimplantation.

CONCLUSION

As patients with inner ear malformations potentially have direct high-pressure anatomical connections between the perilymphatic spaces and the cerebrospinal fluid, they are at risk of hearing loss in the nonimplanted ear during cochlear implantation. This case highlights the need for potential additional patient counseling regarding this risk in the nonimplanted ear.

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.

Cerebrospinal Fluid Leak in Cochlear Implantation: Enlarged Cochlear versus Enlarged Vestibular Aqueduct (Common Cavity Excluded)

Objective. To share our experience of cerebrospinal fluid gusher in cochlear implantation in patients with enlarged cochlear or vestibular aqueduct. Study Design. Case series with comparison and a review of the literature. Methods. A retrospective study was performed. Demographic and radiological results of patients with enlarged cochlear aqueduct or enlarged vestibular aqueduct in 278 consecutive cochlear implant recipients, including children and adults, were evaluated between January 2000 and December 2015. Results. Six patients with enlarged cochlear aqueduct and eight patients with enlarged vestibular aqueduct were identified. Cerebrospinal fluid gusher occurs in five subjects with enlarged cochlear aqueduct and in only one case of enlarged vestibular aqueduct. Conclusion. Based on these findings, enlarged cochlear aqueduct may be the best risk predictor of cerebrospinal fluid gusher at cochleostomy during cochlear implant surgery despite enlarged vestibular aqueduct.

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.