Georges Lamas

The role of cervical and ocular vestibular evoked myogenic potentials in the assessment of patients with vestibular schwannomas.

Objectives To investigate the clinical utility of VEMPs in patients suffering from unilateral vestibular schwannoma (VS) and to determine the optimal stimulation parameter (air conducted sound, bone conducted vibration) for evaluating the function of the vestibular nerve. Methods Data were obtained in 63 patients with non-operated VS, and 20 patients operated on VS. Vestibular function was assessed by caloric, cervical and ocular VEMP testing. 37/63 patients with conclusive ACS ocular VEMPs responses were studied separately. Results In the 63 non-operated VS patients, cVEMPs were abnormal in 65.1% of patients in response to AC STB and in 49.2% of patients to AC clicks. In the 37/63 patients with positive responses from the unaffected side, oVEMPs were abnormal in 75.7% of patients with ACS, in 67.6% with AFz and in 56.8% with mastoid BCV stimulation. In 16% of the patients, VEMPs were the only abnormal test (normal caloric and normal hearing). Among the 26 patients who did not show oVEMP responses on either side with ACS, oVEMPs responses could be obtained with AFz (50%) and with mastoid stimulation (89%). Conclusions The VEMP test demonstrated significant clinical value as it yielded the only abnormal test results in some patients suffering from a unilateral vestibular schwannoma. For oVEMPs, we suggest that ACS stimulation should be the initial test. In patients who responded to ACS and who had normal responses, BCV was not required. In patients with abnormal responses on the affected side using ACS, BCV at AFz should be used to confirm abnormal function of the superior vestibular nerve. In patients who exhibited no responses on either side to ACS, BCV was the only approach allowing assessment of the function of the superior vestibular nerve. We favor using AFz stimulation first because it is easier to perform in clinical practice than mastoid stimulation.

Saccadic Velocity in the New Suppression Head Impulse Test: A New Indicator of Horizontal Vestibular Canal Paresis and of Vestibular Compensation

Objective To determine whether saccadic velocity in the suppression head impulse paradigm (SHIMP) test is a reliable indicator of vestibular loss at the acute and at the chronic stage in patients suffering from different vestibular pathologies. Methods Thirty-five normal subjects and 57 patients suffering from different vestibular pathologies associated with unilateral vestibular loss (UVL) or bilateral vestibular loss (BVL) were tested in the SHIMPs paradigm. SHIMPs were performed by turning the head 10 times at high velocities to the left or right side, respectively. The patients were instructed to fixate on a red spot generated by a head-fixed laser projected on the wall. In this SHIMPs paradigm, healthy subjects made a large anti-compensatory saccade at the end of the head turn (a SHIMP saccade). The peak saccadic velocity, the percentage of the trials completed with saccades in 10 trials, and the latency of the saccades were quantified in each group. A video-head impulse test (v-HIT) was systematically performed in all of our subjects as well as a caloric test. The dizziness handicap inventory questionnaire was also given to chronic UVL and BVL patients. Results At the acute stage after a complete UVL, patients had zero or a few anti-compensatory saccades for low velocity head turns toward the lesioned side. These saccades had lower velocity than the anti-compensatory saccades recorded during head rotation toward the intact side and/or compared with the saccades measured in control subjects. At the chronic stage, some of the patients recovered the ability to perform SHIMP saccades at each head turn toward the lesioned side, but very often these saccades were of significantly lower velocity. In BVL patients, no anti-compensatory saccades, or only significantly smaller ones, could be detected for head turns to both sides. Conclusion SHIMP is a specific and sensitive test to detect a complete horizontal canal loss at the acute stage. In addition, it reflects the ability of patients with moderate horizontal vestibulo–ocular reflex gain decrease to generate anti-compensatory saccades in the chronic stage. In association with v-HIT, it allows determination of the residual vestibular function and to detect anti-compensatory saccades.

Absence of Rotation Perception during Warm Water Caloric Irrigation in Some Seniors with Postural Instability.

Falls in seniors are a major public health problem. Falls lead to fear of falling, reduced mobility, and decreased quality of life. Vestibular dysfunction is one of the fall risk factors. The relationship between objective measures of vestibular responses and age has been studied. However, the effects of age on vestibular perception during caloric stimulation have not been studied. Twenty senior subjects were included in the study, and separated in two groups: 10 seniors reporting postural instability (PI) and exhibiting absence of vestibular perception when they tested with caloric stimulation and 10 sex- and age-matched seniors with no such problems (controls). We assessed vestibular perception on a binary rating scale during the warm irrigation of the caloric test. The function of the various vestibular receptors was assessed using video head impulse test (vHIT), caloric tests, and cervical and ocular vestibular-evoked myogenic potentials. The Equitest was used to evaluate balance. No horizontal canal dysfunction assessed using both caloric test and vHIT was detected in either group. No significant difference was detected between PI and control groups for the peak SPV of caloric-induced ocular nystagmus or for the HVOR gain. All the controls perceived rotation when the maximal SPV during warm irrigation was equal to or ≥15°/s. None of the subjects in the PI group perceived rotation even while the peak SPV exceeded 15°/s, providing objective evidence of normal peripheral horizontal canal function. All the PI group had abnormal Equitest results, particularly in the two last conditions. These investigations show for the first time that vestibular perception can be absent during a caloric test despite normal horizontal canal function. We call this as dissociation vestibular neglect. Patients with poor vestibular perception may not be aware of postural perturbations and so will not correct for them. Thus, falls in the elderly may result, among other factors, from a vestibular neglect due to an inappropriate central processing of normal vestibular peripheral inputs. That is, failure to perceive rotation during caloric testing when the SPV is >15°/s, should prompt the clinician to envisage preventive actions to avoid future falls such as rehabilitation.

Supramaximal stimulation during intraoperative facial nerve monitoring as a simple parameter to predict early functional outcome after parotidectomy

Abstract Conclusion: A supramaximal stimulation at 2 mA during intraoperative electromyographic (EMG) facial nerve monitoring appears to be a simple and effective parameter to predict immediate postoperative injury. Objectives: To assess the role of systematic intraoperative facial nerve monitoring in predicting the early functional outcomes obtained after parotidectomy. Methods: Data were collected from patients who underwent parotidectomy. Intraoperative EMG monitoring of the facial nerve was performed by registering two parameters, event intensity (>100 μV) and amplitude of response after a supramaximal stimulation at 2 mA, at the beginning and end of gland removal. Early postoperative clinical functional facial nerve disorder was assessed at day 2. Results: Overall, 50 patients were included and an early facial dysfunction was detected in 27 cases (54%). The maximal response amplitude after supramaximal stimulation at the trunk of the facial nerve was higher in patients with normal facial function compared with those with poor outcomes at the end of surgery (p < 0.01). The postdissection to predissection ratios of maximal response amplitude, but not the stimulation thresholds, were indicative of a nerve conduction block and were significantly lower in the patient group with a poor outcome compared with the group with a normal facial outcome (p < 0.02).

Early functional results using the nitibond prosthesis in stapes surgery

Abstract Conclusion: The NiTiBOND® prosthesis allows early results to be obtained similar to those with a manually crimped prosthesis fitted by experienced surgeons, thus reducing the learning curve in this critical step of the procedure. Objective: To analyze the 1-month results using the nitinol NiTiBOND® prosthesis in primary otosclerosis surgery and to compare the results with those obtained with fully fluoroplastic or fully titanium pistons. Materials and methods: Fifty consecutive cases operated on with the NiTiBOND® prosthesis (nitinol group) were compared with 50 cases operated on with a fully fluoroplastic piston (fluoroplastic group), and with 131 cases operated on with a fully titanium piston (first titanium group), and also with 50 cases operated on with the same titanium piston just before using the NiTiBOND® piston (last titanium group). Pure-tone and speech audiometry was performed 1 month after surgery for the nitinol group. Comparison was made between the early hearing results of the four groups. Results: The mean air–bone gap closure for the nitinol group was 16 ± 1.0 dB (mean ± SEM, n = 50); an air–bone gap of <15 dB and <10 dB was obtained in 100% and 84% of cases, respectively. These hearing results were similar to the last titanium group and significantly better than those observed in the fluoroplastic and first titanium groups.

Role of electrophysiology in guiding near-total resection for preservation of facial nerve function in the surgical treatment of large vestibular schwannomas

OBJECTIVE In large vestibular schwannoma (VS) surgery, the facial nerve (FN) is at high risk of injury. Near-total resection has been advocated in the case of difficult facial nerve dissection, but the amount of residual tumor that should be left and when dissection should be stopped remain controversial factors. The objective of this study was to report FN outcome and radiological results in patients undergoing near-total VS resection guided by electromyographic supramaximal stimulation of the FN at the brainstem. METHODS This study was a retrospective analysis of a prospectively maintained database. Inclusion criteria were surgical treatment of a large VS during 2014, normal preoperative FN function, and an incomplete resection due to the strong adherence of the tumor to the FN and the loss of around 50% of the response of supramaximal stimulation of the proximal FN at 2 mA. Facial nerve function and the amount and evolution of the residual tumor were evaluated by clinical examination and by MRI at a mean of 5 days postoperatively and at 1 year postoperatively. RESULTS Twenty-five patients met the inclusion criteria and were included in the study. Good FN function (Grade I or II) was observed in 16 (64%) and 21 (84%) of the 25 patients at Day 8 and at 1 year postoperatively, respectively. At the 1-year follow-up evaluation (n = 23), 15 patients (65%) did not show growth of the residual tumor, 6 patients (26%) had regression of the residual tumor, and only 2 patients (9%) presented with tumor progression. CONCLUSIONS Near-total resection guided by electrophysiology represents a safe option in cases of difficult dissection of the facial nerve from the tumor. This seems to offer a good compromise between the goals of preserving facial nerve function and achieving maximum safe resection.

Imaging Criteria to Predict Surgical Difficulties During Stapes Surgery

BACKGROUND AND PURPOSE Stapes surgery for otosclerosis can be challenging if access to the oval window niche is restricted. The aim of this study was to determine the accuracy of the computed tomographic (CT) scan in the evaluation of anatomical distances, and to analyze its reliability in predicting surgical technical difficulties. MATERIAL AND METHODS A total of 96 patients (101 ears) were enrolled in a prospective study between 2012 and May 2015. During surgery, we evaluated the distance D1 between the stapes and the facial nerve, distance D2 between the promontory and the facial nerve after ablation of the superstructure, and the intraoperative discomfort of the surgeon. On preoperative CT scans, we measured the width and depth of the oval window niche, and the angle formed by two axes starting from the center-point of the footplate, the first tangential to the superior wall of the promontory, and the second tangential to the inferior wall of the fallopian canal. RESULTS Intraoperative distances D1 and D2 were correlated with the width of the oval window and with the facial-promontory angle measured on imaging. CT scan measurements of the facial-promontory angle and width of the oval window were associated with the degree of discomfort of the surgeon. The cut-off threshold for intraoperative subjective discomfort was computed as 1.1 mm for the width of the oval window niche, with a sensibility of 71% and a specificity of 84%. CONCLUSION Preoperative imaging analysis of the oval window width and the facialpromontory angle can predict operative difficulty in otosclerosis surgery.