The Association Between Modiolar Base Anomalies and Intraoperative Cerebrospinal Fluid Leakage in Patients With Incomplete Partition Type-II Anomaly: A Classification System and Presentation of 73 Cases

A novel three-step process for the identification of inner ear malformation types

Objective

We hypothesize that visualizing inner-ear systematically in both cochlear view (oblique coronal plane) and in mid-modiolar section (axial plane) and following three sequential steps simplifies, identification of inner-ear malformation types.

Methods

Pre-operative computer-tomography (CT) scans of temporal bones of 112 ears with various inner ear malformation (IEM) types were taken for analysis. Images were analyzed using DICOM viewers, 3D slicer, and OTOPLAN®. The inner-ear was captured in the oblique-coronal plane for the measurement of length and width of cochlear basal turn which is also called as A-, and B-values respectively (Step 1). In the same plane, the angular-turns of lateral-wall (LW) of cochlear basal turn were measured (Step 2). As Step 3, the mid-modiolar section of inner ear was captured in the axial plane by following the A-value and perpendicular to cochlear view. From the mid-modiolar section, the outer-contour of inner ear was captured manually by following contrasting gray area between fluid filled and bony promontory and was compared to known resembling objects to identify IEM types (Step 3).

Results

Following reference values have emerged from our analysis: A-, and B-values (Step 1) on average are >8 mm and >5.5 mm respectively, in normal cochleae (NA), enlarged vestibular aqueduct syndrome (EVAS), incomplete partition (IP) type-I and -II, whereas it is <8 mm and <5.5 mm respectively, in IP type-III and cochlear hypoplasia (CH). Angular-turn of LW is consistently observed in cochlear basal turn (Step 2), is 540° in NA and EVAS, 450° in IP-II, and 360° in IP types I & III. In subjects with CH type, angular-turn of LW is either 360° or 450° or 540°. In true mid-modiolar section, outer-contour of inner-ear (Step-3), other than in CH and cystic inner-ear malformations, resembles recognizable shapes of known objects. Absence of EVA is an additional characteristic that confirms diagnosis of CH when the A-, B-values, and angular-turn of LW can be similar to other anatomical types. Drawing a straight line along posterior edge of internal auditory canal (IAC) in axial view can differentiate a true common cavity (CC) from cochlear aplasia-vestibular cavity (VC).

Conclusion

Three-step process proposed in this study captures inner-ear in cochlear view as well in mid-modiolar sections visualizing key features of inner-ear in identification of IEM types.

Level of Evidence

Level 1.

Cochlear Pathomorphogenesis of Incomplete Partition Type II in Slc26a4-Null Mice

Incomplete partition type II (IP-II) is frequently identified in ears with SLC26A4 mutations. Cochleae with IP-II are generally observed to have 1½ turns; the basal turns are normally formed, and the apical turn is dilated or cystic. The objective of this study was to characterize the pathomorphogenesis of the IP-II cochlear anomaly in Slc26a4-null mice. Otic capsules were dissected from Slc26a4^Δ/+ and Slc26a4^Δ/Δ mice at 1 and 8 days of age and at 1 and 3 months of age. X-ray micro-computed tomography was used to image samples. We used a multiplanar view and three-dimensional reconstructed models to calculate the cochlear duct length, cochlear turn rotation angle, and modiolus tilt angle. The number of inner hair cells was counted, and the length of the cochlear duct was measured in a whole-mount preparation of the membranous labyrinth. X-ray micro-computed tomography mid-modiolar planar views demonstrated cystic apical turns in Slc26a4^Δ/Δ mice resulting from the loss or deossification of the interscalar septum, which morphologically resembles IP-II in humans. Planes vertical to the modiolus showed a similar mean rotation angle between Slc26a4^Δ/+ and Slc26a4^Δ/Δ mice. In contrast, the mean cochlear duct length and mean number of inner hair cells in Slc26a4^Δ/Δ mice were significantly smaller than in Slc26a4^Δ/+ mice. In addition, there were significant differences in the mean tilt angle and mean width of the modiolus. Our analysis of Slc26a4-null mice suggests that IP-II in humans reflects loss or deossification of the interscalar septum but not a decreased number of cochlear turns.

Imaging of inner ear malformations: a primer for radiologists

In the multidisciplinary management of patients with inner ear malformations (IEMs), the correct diagnosis makes the differences in terms of clinical and surgical treatment. The complex anatomical landscape of the inner ear, comprising several small structures, makes imaging of this region particularly challenging for general radiologists. Imaging techniques are important for identifying the presence and defining the type of IEM and the cochlear nerve condition. High-resolution magnetic resonance imaging (MRI) sequences and high-resolution computed tomography (HRCT) are the mainstay imaging techniques in this area. Dedicated MRI and HRCT protocols play an important role in the diagnosis and treatment of patients with inner ear disease. The most suitable technique should be selected depending on the clinical setting. However, in cases of congenital malformation of the inner ear, these techniques should be considered complementary. Since prompt intervention has a positive impact on the treatment outcomes, early diagnosis of IEMs is very important in the management of deaf patients. This article reviews the key concepts of IEMs for clinical radiologists by focusing on recent literature updates, discusses the principal imaging findings and clinical implications for every IEM subgroup, thus providing a practical diagnostic approach.

Surgical Outcomes With Cochlear Implantation in Patients With Enlarged Cochlear Aperture: A Systematic Review

OBJECTIVE

Evaluate surgical outcomes in patients with enlarged cochlear aperture (ECA) after cochlear implantation.

DATABASES REVIEWED

PubMed, EMBASE, and Scopus.

METHODS

A systematic review was performed using standardized methodology. Studies were included if they included subjects with ECA who underwent cochlear implantation. Exclusion criteria included non-English articles, abstracts, letters/commentaries, case reports, and reviews. Bias was assessed using the Risk of Bias in Non-randomized Studies of Interventions (ROBINS-I) tool.

RESULTS

Out of 1,688 identified articles, 7 articles representing 23 subjects with ECA were included. Publication rates increased between the period of study from 2009 to 2018. Four studies were level 4 evidence and three studies were level 3 evidence. In total, 20 subjects underwent cochlear implantation. Cerebrospinal fluid gushers were encountered in the majority of cases that reported complications (16/17, 94.1%); one patient developed postoperative meningitis, and another experienced postimplantation facial nerve stimulation. No study provided measurements on cochlear aperture size or defined size criteria used to identify ECA. Four studies recognized X-linked deafness to be associated with ECA, and the most common mutation was in POU3F4 gene.

CONCLUSION

An association exists between ECA and cerebrospinal fluid gusher, underscoring the importance of reviewing preoperative imaging. Size criteria are not well defined, and there is a paucity of data with respect to normative measurements. Many cases of ECA may give a genetic link. Although level of evidence of current studies remains modest, ECA reports have increased and will likely continue to expand with advancements in imaging and genetic testing.

Peristapedial bulb: an indicator of spontaneous CSF leak in cochlear candidates with Mondini dysplasia

BACKGROUND

Mondini dysplasia with spontaneous cerebrospinal fluid (CSF) leak is rare in cochlear implantation (CI) candidates but lethal. Detailed evaluation and surgical intervention are needed for these patients.

AIM/OBJECTIVE

To report our findings of the peristapedial bulb in computer tomography (CT) as diagnostic evidence of spontaneous CSF leak and discuss its clinical value to direct the surgical plan for patients with profound sensorineural hearing loss (SNHL) and meningitis.

MATERIAL AND METHODS

A retrospective review was conducted, including patients' demographic features, radiographic examination, operation records, auditory/speech evaluation. The patients presented with a peristapedial bulb were included.

RESULTS

In 2775 CI recipients, 7 out of 219 (3.2%) patients with Mondini anomaly had detectable peristapedial bulbs in HRCT, among whom 6 patients have a history of meningitis. Surgical exploration verified the radiographic findings in 6 out of 7 patients. All patients received CI and vestibular obliteration. Control of meningitis was acceptable. The threshold of hearing significantly decreased from 74.1 dB ± 6.9 dB to 37.1 ± 4.8 dB after CI and the word recognition score elevated from 21.4 ± 14.9% to 78.6 ± 9.3%.

CONCLUSIONS AND SIGNIFICANCE

Peristapedial bulb is an indicator of spontaneous CSF leak in patients with profound SHNL and Mondini anomaly. Patients will benefit from CI and surgical intervention.

Pre- and post-operative imaging of cochlear implants: a pictorial review

Cochlear implants are increasingly used to treat sensorineural hearing disorders in both children and adults. Pre-operative computed tomography and magnetic resonance imaging play a pivotal role in patient selection, to rule out findings that preclude surgery or identify conditions which may have an impact on the surgical procedure. The post-operative position of the electrode array within the cochlea can be reliably identified using cone-beam computed tomography. Recognition of scalar dislocation, cochlear dislocation, electrode fold, and malposition of the electrode array may have important consequences for the patient such as revision surgery or adapted fitting.