Variability of the mental representation of the cochlear anatomy during cochlear implantation.

The aim of this study was to assess the mental representation of the insertion axis of surgeons with different degrees of experience, and reproducibility of the insertion axis in repeated measures. A mastoidectomy and a posterior tympanotomy were prepared in five different artificial temporal bones. A cone-beam CT was performed for each temporal bone and the data were registered on a magnetic navigation system. In these five temporal bones, 16 surgeons (3 experts; >50 cochlear implant surgery/year; 7 fellows with few cochlear implant experience, and 6 residents) were asked to determine the optimal insertion axis according to their mental representation. Compared to a planned ideal axis, the insertion axis was better determined by the experts with higher accuracy (axial: 7° ± 1.5°, coronal: 6° ± 1.5°) than fellows (axial: 14° ± 1.7°, coronal: 13° ± 1.7°; p < 0.05), or residents (axial: 15° ± 1.5°; p < 0.001, coronal: 17° ± 1.9°; p < 0.001). This study suggests that mental representation of the cochlea is experience-dependent. A high variation of the insertion axis to the scala tympani can be observed due to the complexity of the temporal bone anatomy and lack of landmarks to determine scala tympani orientation. Navigation systems can be used to evaluate and improve mental representation of the insertion axis to the scala tympani for cochlear implant surgery.

Confrontation of endolymphatic hydrops diagnosis on 3-Tesla MRI to clinical and audiovestibular findings in Meniere's disease.

Objective: The aim of this study was to compare different MRI diagnostic criteria for endolymphatic hydrops (EH) and to investigate the relation between audiovestibular and MRI findings in Meniere's disease (MD). Materials and methods: Prospective cross-sectional cohort study in 2 referral centers included 76 patients with unilateral (n = 62) or bilateral (n = 14) MD. All patients underwent inner ear 3T-MRI 4 h (n = 52) or >24H (n = 24) following audiovestibular tests. T2-CISS and 3D-FLAIR images 4H after gadolinium were obtained. EH diagnosis was based on saccular morphology on coronal views (T2 and 3D-FLAIR), semi quantitative estimation of endolymphatic space enlargement, and saccule utricle ratio inversion (SURI) on 3D-FLAIR axial views. Results: SURI was the best criterion related to the disease side (43 SURI+ on symptomatic ears, n = 77, vs. 6 SURI+ on asymptomatic ears, n = 53, p < 0.0001, Chi-2). Same-day MRI revealed relation between EH, hearing loss and caloric weakness which could not be detected on delayed MRI: SURI was associated with a higher pure-tone average (43 ± 4.1 dB in SURI+ ears, n = 42 vs. 23 ± 2.6 SURI-, n = 62, p < 0.0001, unpaired t-test,), and a higher proportion of vestibular caloric weakness (23/46 SURI+ ears vs. 4/62 SURI-, p < 0.001, Chi-2). Among all criteria, SURI combined to caloric weakness was the best predictor of the affected side in a logistic regression model. Conclusion: SURI had the strongest relation to the side the disease and audio vestibular findings for unilateral, probable and definite meniere disease. A short delay between MRI and audio vestibular tests improved the coherence between the findings.

Minimally invasive computer-assisted approach for cochlear implantation: a human temporal bone study.

Computer-assisted navigation systems can now potentially guide the surgeon to the cochlea with a trajectory avoiding the facial nerve through a keyhole approach. Five temporal bone specimens, with 4 titanium screws placed in the mastoid cortex, were studied. Preoperative computed tomographic scan images were loaded on an electromagnetic computer-assisted surgery (CAS) system (Digipointeur, Collin, Bagneux, France). A drill was connected to the CAS to monitor its progression continuously. A conical approach passing through the facial recess and ending in the scala tympani was performed. A 0.5-mm wire was inserted into the cochlea. The keyhole approach was technically feasible in all cases. No facial nerve injury was observed on imaging and dissection control. The wire was positioned in the scala tympani and the position accuracy of the CAS was <0.76 mm on the target in all cases. The CAS system with fiducial markers yielded sufficient precision to allow a minimally invasive approach to the cochlea.

Detection of perilymphatic fistula in labyrinthine windows by virtual endoscopy and variation of reconstruction thresholds on CT scan.

Background: Perilymphatic fistula (PLF) is a breach in a labyrinthine window. The opening might decrease the radiological density of the window.Aims/objectives: To evaluate the radiological density of the labyrinthine windows by virtual endoscopy on CT scan.Materials and methods: This prospective study included 47 adult patients with PLF and 98 control patients. Diagnosis of PLF was based on a composite radio clinical score and/or intra operative visualization of the fistula and/or resolution of the symptoms after surgery. On routine CT-scan, labyrinthine windows were examined by virtual endoscopy. The reconstruction threshold was gradually increased until a virtual opening appeared (opening threshold [OT]) and compared to the contralateral window (OT difference).Results: The OT difference was higher in patients than in controls (60.2 ± 10.36 (SEM), n = 47 versus 28.0 ± 2.29 Hounsfield units (HUs), n = 98, p < .01 unpaired t-test). A ROC analysis showed that at an OT difference of 31.5 UH had a sensitivity of 75% and a specificity of 75% for the PLF diagnosis.Conclusions: CT-scan virtual endoscopy and threshold variation provided high specificity and sensitivity in the PLF diagnosis.Significance: This post processing of radiological data appears to enhance the diagnostic value of CT scan.

An Optimized Robot-Based Technique for Cochlear Implantation to Reduce Array Insertion Trauma.

OBJECTIVE: To compare the intracochlear trauma induced by optimized robot-based and manual techniques with a straight electrode array prototype inserted at different lengths. STUDY DESIGN: Experimental study. SETTING: Robot-based otologic surgery laboratory. SUBJECTS AND METHODS: A prototype array was inserted at different insertion lengths (21 and 25 mm) in 20 temporal bones. The manual insertion was performed with a microforceps. The optimized approach consisted of an optimal axis insertion provided by a robot-based arm controlled by a tracking system, with a constant speed of insertion (0.25 mm/s) achieved by a motorized insertion tool. The electrode position was determined at the level of each electrode by stereomicroscopic cochlea section analysis. RESULTS: A higher number of electrodes correctly located in the scala tympani was associated with the optimized approach ( P = .03, 2-way analysis of variance). Regardless of the insertion technique used, the array inserted at 25 mm allowed complete insertion of the active stimulating portion of the array in all cases. Insertion depth was greater when the array was inserted to 25 mm versus 21 mm ( P < .001, 2-way analysis of variance). The optimized insertion was associated with less trauma than that from manual insertion regardless the length of the inserted array ( P = .04, 2-way analysis of variance). CONCLUSION: Compared with a manual insertion, intracochlear trauma could be reduced with array insertion performed on an optimal axis by using motorized insertion and by applying a constant insertion speed.

Cochlear Implant Insertion Axis Into the Basal Turn: A Critical Factor in Electrode Array Translocation.

HYPOTHESIS: An inappropriate insertion axis leads to intracochlear trauma during cochlear implantation (CI). BACKGROUND: Few studies assessed the relationship between the insertion axis and the electrode scalar location. METHODS: Preimplantation cone-beam CT (CBCT) was performed on 12 human temporal bones. In five temporal bones, an optimal insertion axis was planned, due to the impossibility to attain the ST centerline from the posterior tympanotomy, because of facial canal position. In the seven other temporal bones, an inaccurate insertion axis was intentionally planned (optimal axis+15 degrees). Automated CI array insertion according to the planned axis was performed with a motorized insertion tool driven by a navigated robot-based arm. The cochlea and basilar membrane were segmented from the preimplantation CBCT and the array segmented from the postimplantation CBCT to construct a merged final three-dimensional (3D) model. Microscopical and 3D analysis were performed to determine the intracochlear trauma at the level of each electrode. RESULTS: A good agreement was observed in determining electrode position between microscopic analysis and the 3D model (Cohen's kappa k = 0.67). The angle of approach to the ST centerline was associated with the number of electrodes inserted into the ST (r = -0.65, p = 0.02, [95% CI -0.90 to -0.11] Spearman's rank correlation). CONCLUSION: A 3D reconstruction model was effective in determining the array position in the cochlea scalae. Our data indicate that the angle of approach to the ST centerline is a critical factor in intracochlear trauma. Additional studies should be conducted to assess the importance of the insertion axis with other array designs.

Cone beam computed tomography and histological evaluations of a straight electrode array positioning in temporal bones.

CONCLUSION: CBCT allows a precise evaluation of the dimensions and of the shape of the cochlear duct that is of primary importance for the choice of the length and the design of the electrode array. This radio-histological study confirms that CBCT is a reliable tool to be used in clinical studies to evaluate the position of straight electrode arrays within the cochlear scala. OBJECTIVE: To validate the reliability of cone beam computed tomography (CBCT) in the evaluation of cochlear anatomy and positioning of a straight electrode array, by comparing radiological images to histological analysis of cochlear implanted temporal bones. METHODS: Eight temporal bones for four subjects were analysed before and after cochlear implantation with a straight electrode array. The size of the cochlea, the dimensions, and shape of the cochlear duct at 180° and 360° were evaluated on CBCT performed before implantation. Temporal bones then underwent histological analysis to determine the position of the electrode array. Scalar localization of the electrode array was assessed on CBCT performed after implantation, and compared with histological study. RESULTS: CBCT is a reliable radiological technique to differentiate variability not only of cochlear dimensions, but also of size and shape of the cochlea. Histological analysis confirmed the scalar position of the electrode array assessed by the CBCT in 7/8 temporal bones, but soft tissue trauma such as dissection of the spiral ligament was not identified by the CBCT.

Detection of labyrinthine fistulas in human temporal bone by virtual endoscopy and density threshold variation on computed tomographic scan.

OBJECTIVE: To assess the sensitivity of the routine computed tomographic (CT) scan of the temporal bone coupled to a virtual endoscopy, with density threshold variation, in detecting small fistulas in human temporal bone specimens. DESIGN: Single-blind, before-after trial. SETTING: This study was carried out in a research laboratory in collaboration with a radiology department. PATIENTS: Five human adult temporal bone specimens were included. INTERVENTIONS: The fistulas were created with calibrated burrs (0.3, 0.5, and 0.8 mm) in the 3 semicircular canals and in the promontory of 3 temporal bones. Two other temporal bones served as controls. All bones underwent CT scan (1-mm section thickness) before and after dissection. Three-dimensional images were obtained from CT scan native axial views at different density reconstruction thresholds. The virtual endoscope was placed in the middle ear cavity looking to the inner ear wall. The threshold at which a bony defect appeared on virtual endoscopic images (opening threshold in Hounsfield units [H]) was noted for each location. MAIN OUTCOME MEASURES: Opening thresholds before and after dissection. RESULTS: On standard axial views, fistulas smaller than 0.5 mm were not visualized. By virtual endoscopy, all fistulas could be visualized. The opening threshold decreased after fistula creation in the semicircular canals (1244 +/- 50.5 H [n = 36] vs 778 +/- 52.4 H [n = 34]; P<.001; 1-way analysis of variance and Dunnett multiple comparisons posttest) and in the promontory (1541 +/- 37.8 H [n = 12] vs 1334 +/- 35.1 H [n = 8]; P<.001). The opening thresholds in the control specimens remained unchanged after dissection. CONCLUSION: Virtual endoscopy with variation of reconstruction threshold allows the detection of small labyrinthine fistulas with diameters of 0.3 mm or smaller.

Inflammatory obstruction of the olfactory clefts and olfactory loss in humans: a new syndrome?

The first step in the olfactory perception is the activation by odorants of sensory neurones in the olfactory epithelium. In humans, this sensory epithelium is located at 2 narrow passages, the olfactory clefts, at the upper part of the nasal cavities. Little is known about the physiology of these clefts. We examined, in 34 patients, the impact of obstructed clefts upon detection and postlearning identification of 5 odorants. The location and extension of the obstructions were assessed using endoscopy, CT scans, and MRI. The inflammatory obstruction was usually bilateral, extending anteroposteriorly, and confined to the clefts, with no sign of obstruction or any inflammatory disease in the rest of the nasal cavities and sinuses. When tested with 5 odorants, these patients showed greatly impaired olfaction compared with a group of 73 normosmic subjects. The majority of these 34 patients had sensory deficits equivalent to that found in another group of 41 congenital anosmic patients, where inspection with MRI indicated the lack of olfactory bulbs. This study demonstrates that the olfactory clefts, in human, function as an entity that is different from other regions of the nasal cavity and is the target for local inflammatory events that are apparently not responding to corticoid and antibiotic treatments.