Superior semicircular canal dehiscence in relation with the superior petrosal sinus: our experience, surgical management and systematic review of literature.

PURPOSE: Most of Superior Semicircular Canal Dehiscence (SSCD) are located in the apical region of the SSC. However, in a small number of cases, it may be situated in the medial wall, causing the SSC to contact with the superior petrosal sinus (SPS). The aim of this study is to describe four patients with SSCD involving the superior petrosal sinus (SSCD-SPS) and to perform a review of the literature. METHODS: Observational retrospective study of patients diagnosed of SSCD-SPS in a tertiary referral center. A systematic review was made, identifying 7 articles in the literature. Clinical presentation, complementary test (pure-tone audiometry, PTA; vestibular evoked myogenic potential, VEMP; computed tomography, CT), therapeutic management and outcomes were reported. RESULTS: Four new cases of SSCD-SPS are reported, in three of them a transmastoid plugging was performed. 54 patients with SSCD-SPS (57 dehiscences) were reported in the literature. The most frequent symptoms were aural pressure (57.41%) and vertigo provoked by pressure/Valsalva (55.55%). Conductive hearing loss was the most common finding in PTA (47.37%). Abnormally low thresholds were observed in 59.46% of reported VEMP. Transmastoid approach was used in ten cases, middle fossa approach in four, round window reinforcement in one, and occlusion of the SPS using coils in two. CONCLUSIONS: Within SSCD, we have encountered a rare subtype characterized by its medial wall location in close proximity to the SPS. This subgroup needs special consideration as it has shown its own distinct characteristics. Regarding therapeutic management, we advocate a transmastoid approach.

An anatomical study of the sigmoid sinus artery: Application to the transmastoid approach.

INTRODUCTION: We aimed to investigate the morphological features of the artery that traverse the sigmoid sinus's lateral surface and to discuss this structure's clinical relevance. METHODS: Ten sides from five cadaveric Caucasian heads were used for gross anatomical dissection to investigate the morphological features of the sigmoid sinus artery (SSA), and additional five sides were used for histological observation. RESULTS: The SSA was found on eight out of ten sides (80%). The mean diameter of the SSA was 0.3 mm. The mean distance from the tip of the mastoid process to the artery was 20.3 mm. Histological observation identified extradural and intradural courses of SSA. The intradural course was further categorized into protruding and non-protruding types. In the protruding type, the SSA traveled within the dura but indented into the bone, making it more or less an intraosseous artery. In the non-protruding type, the SSA traveled within the dura but did not protrude into the bone but rather indented into the lumen of the SS. In all sections, both intradural and extradural courses were identified simultaneously. CONCLUSIONS: When the mastoid foramen is observed, it does not always only carry an emissary vein but also an artery. The SSA could be considered a "warning landmark" during bone drilling for the transmastoid approach.

Long-term outcomes of facial nerve decompression by transmastoid versus middle cranial fossa approach for traumatic facial paralysis.

OBJECTIVES: To evaluate and compare the long-term results of patients who underwent facial nerve decompression surgery with either transmastoid-supralabyrinthine (TMSL) or combined transmastoid- middle cranial fossa (MCF) approach for traumatic facial nerve paralysis. MATERIALS AND METHODS: This is a single-center retrospective case-control study. The medical records of traumatic facial paralysis patients with House Brackmann (HB) Grade 6 who underwent facial nerve decompression surgery at via either TMSL or MCF approach between January 2011 and December 2017 were reviewed. The patients who had otic capsule involvement and total sensorineural hearing loss, therefore underwent translabyrinthine facial nerve decompression, and the patients follow-up period has not yet reached four years were excluded from the study. Postoperative HB score and hearing status were compared. RESULTS: Eleven patients were operated with MCF approach (group 1), while 9 patients with TMSL approach (group 2). Average age of patients was 20.04 + 15.2 (range:4-47) years. Three (15 %) patients were female, while 17 (85 %) was male. Geniculate ganglion (90 %) was the most affected segment of the facial nerve. Facial nerve edema was observed in all cases, while intraneural hematoma were encountered in 4 (20 %) cases. Statistically significant improvement in median HB scores were reached in both groups, and no significant difference was observed in post-operative HB scores between both techniques. No significant difference in median AC 0,5-4 khZ and BC 0,5-3 kHz thresholds was observed between both techniques. CONCLUSION: Even middle fossa approach is the best surgical technique to explore geniculate ganglion and labyrinthine segment of facial nerve, the functional results of transmastoid supralabrynthine approach, which is not needed craniotomy with low complication rate are as successful as middle fossa approach in selected patients.

Vestibular schwannoma extending into the tympanic cavity and jugular fossa by invasion of the petrous bone.

Vestibular schwannomas usually originate in the internal acoustic meatus, and gradually extends into the cerebellopontine cistern. Invasive growth into the petrous bone is extremely rare. We describe a case of a vestibular schwannoma that aggressively extended into the petrous bone and extracranial space. This may have arisen because of an unusually peripheral site of origin on the vestibular nerve.

Corticospinal and spinal excitability during peripheral or central cooling in humans.

Cold exposure can impair fine and gross motor control and threaten survival. Most motor task decrement is due to peripheral neuromuscular factors. Less is known about cooling on central neural factors. Corticospinal and spinal excitability were determined during cooling of the skin (Tsk) and core (Tco). Eight subjects (four female) were actively cooled in a liquid perfused suit for 90 min (2 °C inflow temperature), passively cooled for 7 min, and then rewarmed for 30 min (41 °C inflow temperature). Stimulation blocks included 10 transcranial magnetic stimulations [eliciting motor evoked potentials (MEPs) which indicate corticospinal excitability], 8 trans-mastoid electrical stimulations [eliciting cervicomedullary evoked potentials (CMEPs) which indicate spinal excitability] and 2 brachial plexus electrical stimulations [eliciting maximal compound motor action potentials (Mmax)]. These stimulations were delivered every 30 min. Cooling for 90 min reduced Tsk to 18.2 °C while Tco did not change. At the end of rewarming Tsk returned to baseline while Tco decreased by 0.8 °C (afterdrop) (P < 0.001). Metabolic heat production was higher than baseline at the end of passive cooling (P = 0.01), and 7 min into rewarming (P = 0.04). MEP/Mmax remained unchanged throughout. CMEP/Mmax increased by 38% at end cooling (although increased variability at this time rendered the increase insignificant, P = 0.23) and 58% at end warming when Tco was 0.8 °C below baseline (P = 0.02). Cooling increased spinal excitability but not corticospinal excitability. Cooling may decrease cortical and/or supraspinal excitability which is compensated for by increased spinal excitability. This compensation is key to providing a motor task and survival advantage.

Hemorrhage due to a pseudoaneurysm on a dural-pial anastomosis after decompression for Chiari malformation type I: case report.

While intracranial aneurysms rarely develop after neurosurgical procedures, delayed pseudoaneurysm formation after foramen magnum decompression (FMD) has never been reported. A 52-year-old woman presented with an atypical subarachnoid hemorrhage in the posterior fossa 12 years after a FMD for symptomatic Chiari malformation type I was performed. A pseudoaneurysm on a dural-pial anastomosis was identified as the bleeding source and successfully occluded by endovascular means with full clinical recovery of the patient. Injury to the distal posterior inferior cerebellar artery related to surgery and postoperative infection likely caused formation of a dural-pial anastomosis. Additionally, hemodynamic stress or dissection may have contributed to delayed pseudoaneurysm formation and rupture.

Evaluation of the transmastoid plugging approach for superior semicircular canal dehiscences: a retrospective series of 30 ears.

PURPOSE: The classical surgical approach for superior semicircular canal dehiscences (SSCD) is via the extradural middle cranial fossa. This pathway is used to resurface or to plug the SSC. In this paper, we present long-term data on an alternative route: the transmastoid pathway. The predictive factors for a successful surgery are equally presented in this paper. METHODS: Thirty reports of patients operated between September 2007 to January 2020 were analysed. SSCD was confirmed by the association of concordant complaints, audiometric data, cervical vestibular evoked myogenic potentials (cVEMP) responses and computerized tomography findings. Before and after surgery, the following factors were analysed: auditory and vestibular subjective symptoms, Tullio phenomenon, pure-tone audiometry thresholds for air and bone conduction, air-bone gap, cVEMP threshold, and computerized tomography data, for instance the size of the dehiscence. RESULTS: The follow-up is 21 months on average. The transmastoid approach significantly improves all symptoms (although there were less probing results for the vestibular symptoms). Objectively, we can observe, a closure of the audiometric air-bone gap on the low frequencies and an improvement in the cVEMP. The only correlation that was identified was between the preoperative cVEMP results and the postoperative air conduction. CONCLUSIONS: The originality of this study is the long postoperative follow-up. It allowed us to evaluate the symptoms in the long term and to determine a predictive factor of postoperative complication, which has not yet been described until today.The transmastoid plugging technique is safe and effective. Additional long-term data with a larger cohort are needed to confirm our results and correlation studies.

Is Septal Cartilage Graft via Transmastoid Approach Safe Enough in the Repair of Large Tegmen Defects?

INTRODUCTION: Tegmen defect (TD) has a potential of intracranial spread of middle ear infection, meningoencephalic herniation (MEH), and cerebrospinal fluid leakage (CSFL). Especially the defects >1 cm with MEH or CSFL are generally repaired via the classical middle fossa or minicraniotomy technique. The aim of this study was to show the efficiency of the intracranial, extradural placement of the septal cartilage graft in the closure of the TD larger than 1 cm via the transmastoid (TM) approach. METHODS: The demographic, preoperative, intraoperative, and postoperative data of 11 patients with chronic otitis media (COM) who had TD larger than 1 cm were reviewed retrospectively. Hospitalization time and hearing preservation with respect to MEH or CSFL were analyzed. RESULTS: The most common etiology of TD was cholesteatoma (82%), and 91% of the patients had multiple COM surgery history. The mean TD size was 15.4 (10-25) mm. Fifty-five percent of the patients presented with either MEH or CSFL. The mean follow-up of the patients was 22.5 (8-42) months. There was no significant difference between preoperative and postoperative mean bone conduction thresholds. Mean hospitalization time was 5.2 (3-10) days. There was no significant difference in the hospitalization time between patients with MEH or CSFL and without MEH or CSFL. Neither recurrence nor graft infection was encountered. CONCLUSION: Extradural grafting with the septal cartilage in the large TD up to 25 mm can be repaired efficiently via the TM approach without application of a lumbar drainage.

Facial and hearing outcomes in transmastoid nerve decompression for Bell's palsy, with preservation of the ossicular chain.

OBJECTIVES: Facial nerve decompression is a salvage treatment for Bell's palsy patients for whom a poor prognosis is anticipated with standard medical treatment. The transmastoid approach is a frequently performed approach, but it remains unknown if this surgery is effective when the ossicular chain is preserved. This study aimed to determine the efficacy of facial nerve decompression using the transmastoid approach in Bell's palsy. DESIGN, SETTING AND PARTICIPANTS: This retrospective study included patients who had undergone transmastoid facial nerve decompression with ossicular chain preservation and patients who met the criteria for surgery, but received only medical treatment between January 2007 and May 2019, at a single centre. MAIN OUTCOME MEASURES: Attainment of House-Brackmann grade I at 12 months after onset of facial palsy. RESULTS: The recovery rate to House-Brackmann grade I in the decompression group in the early phase (≤18 days after onset) was higher than that of the medical treatment group, although the difference was not significant (70% vs 47%, P = .160). However, within this early surgery group, a subgroup of cases with ≥95% facial nerve degeneration demonstrated a significant improvement in recovery rate (73% vs 30%, P = .018). Among surgeries performed in the late phase (≥19 days), only a subgroup with ≥95% facial nerve degeneration was available for analysis, and the difference in recovery rate was not significant compared with medical treatment alone (26% vs 30%, P = 1.00). Post-surgical hearing evaluation demonstrated that average hearing deterioration was 1.3 dB which was non-significant, suggesting this procedure does not cause hearing loss. CONCLUSIONS: Transmastoid facial nerve decompression with ossicular chain preservation in the early phase after symptom-onset is an effective salvage treatment for severe Bell's palsy with ≥95% facial nerve degeneration.

The effects of forearm position and contraction intensity on cortical and spinal excitability during a submaximal force steadiness task of the elbow flexors.

Elbow flexor force steadiness is less with the forearm pronated (PRO) compared with neutral (NEU) or supinated (SUP) and may relate to neural excitability. Although not tested in a force steadiness paradigm, lower spinal and cortical excitability was observed separately for biceps brachii in PRO, possibly dependent on contractile status at the time of assessment. This study aimed to investigate position-dependent changes in force steadiness as well as spinal and cortical excitability at a variety of contraction intensities. Thirteen males (26 ± 7 yr; means ± SD) performed three blocks (PRO, NEU, and SUP) of 24 brief (~6 s) isometric elbow flexor contractions (5, 10, 25 or 50% of maximal force). During each contraction, transcranial magnetic stimulation or transmastoid stimulation was delivered to elicit a motor-evoked potential (MEP) or cervicomedullary motor-evoked potential (CMEP), respectively. Force steadiness was lower in PRO compared with NEU and SUP (P ≤ 0.001), with no difference between NEU and SUP. Similarly, spinal excitability (CMEP/maximal M wave) was lower in PRO than NEU (25 and 50% maximal force; P ≤ 0.010) and SUP (all force levels; P ≤ 0.004), with no difference between NEU and SUP. Cortical excitability (MEP/CMEP) did not change with forearm position (P = 0.055); however, a priori post hoc testing for position showed excitability was 39.8 ± 38.3% lower for PRO than NEU at 25% maximal force (P = 0.006). The data suggest that contraction intensity influences the effect of forearm position on neural excitability and that reduced spinal and, to a lesser extent, cortical excitability could contribute to lower force steadiness in PRO compared with NEU and SUP.NEW & NOTEWORTHY To address conflicting reports about the effect of forearm position on spinal and cortical excitability of the elbow flexors, we examine the influence of contraction intensity. For the first time, excitability data are considered in a force steadiness context. Motoneuronal excitability is lowest in pronation and this disparity increases with contraction intensity. Cortical excitability exhibits a similar pattern from 5 to 25% of maximal force. Lower corticospinal excitability likely contributes to relatively poor force steadiness in pronation.

Effect of blood flow occlusion on corticospinal excitability during sustained low-intensity isometric elbow flexion.

Blood flow occlusion (BFO) has been used to study the influence of group III/IV muscle afferents after fatiguing exercise, but it is unknown how BFO-induced activity of these afferents affects motor cortical and motoneuronal excitability during low-intensity exercise. Therefore, the purpose of this study was to assess the acute effect of BFO on peripheral [maximal M wave (Mmax)], spinal [cervicomedullary motor evoked potential (CMEP) normalized to Mmax], and motor cortical [motor evoked potential (MEP) normalized to CMEP] excitability. Nine healthy men completed a sustained isometric contraction of the elbow flexors at 20% of maximal force under three conditions: 1) contractile failure with BFO, 2) a time-matched trial without restriction [free flow (FFiso)], and 3) contractile failure with free flow (FFfail). Time to failure for BFO (and FFiso) were ~80% shorter than that for FFfail (P < 0.05). For FFfail and FFiso, Mmax area decreased ~17% and ~7%, respectively (P < 0.05), with no change during BFO. CMEP/Mmax area increased ~226% and ~80% during BFO and FFfail, respectively (P < 0.05), with no change during FFiso (P > 0.05). The increase in normalized CMEP area was greater for BFO and FFfail compared with FFiso and for BFO compared with FFfail. MEP/CMEP area was not different among the protocols (P > 0.05) and increased ~64% with time (P < 0.05). It is likely that group III/IV muscle afferent feedback to the spinal cord modulates the large increase in motoneuronal excitability for the BFO compared with FFfail and FFiso protocols.NEW & NOTEWORTHY We have observed how blood flow occlusion modulates motor cortical, spinal, and peripheral excitability during and immediately after a sustained low-intensity isometric elbow flexion contraction to failure. We conclude that blood flow occlusion causes a greater and more rapid increase in motoneuronal excitability.

Transmastoid presigmoid retrolabyrinthine approach for removal of pontine cavernous malformation: how I do it.

BACKGROUND: Bleeding of brainstem cavernous malformations (BSCM) cause high morbidity and should be treated surgically whenever possible. METHOD: We present a 56-year-old man, who was diagnosed with a BSCM at right pons, which caused functional impairments of dorsal column, spinothalamic tract, cochlear nucleus, and middle cerebellar peduncle. A transmastoid presigmoid retorlabyrinthine approach via the lateral pontine zone (LPZ), with an assistance of imaging guidance and intraoperative neurophysiological monitoring, was performed to completely resect the BSCM. The patient recovered despite a transient worsening of cerebellar sign and hemiparesthesia for 1 week, without surgical complications. CONCLUSIONS: A transmastoid presigmoid retrolabyrinthine approach through LPZ is safe and effective for lateral pontine BSCM resection.

Quality of life outcomes after transmastoid plugging of superior semicircular canal dehiscence.

PURPOSE: This study was performed to evaluate the effectiveness and impact on quality of life in patients undergoing plugging of superior semicircular canal dehiscence using the transmastoid approach. MATERIALS AND METHODS: Retrospective chart review with prospective outcomes assessment, using validated quantitative scoring systems, was performed on 10 patients (23-76 years) who underwent transmastoid plugging of superior semicircular canal dehiscence between February 2014 and February 2018 at a tertiary referral center. Pre-operative and post-operative autophony and vertigo were measured by The Autophony Index and the Dizziness Handicap Index. Overall quality of life following intervention was measured by the Glasgow Benefit Inventory. Subjective improvement, audiological changes, and subjective quality of life changes were also recorded. RESULTS: A significant reduction in the total Dizziness Handicap Index was seen following transmastoid repair of superior semicircular canal dehiscence (p = 0.0078). This was also evident when subgroup analysis of the Dizziness Handicap Index was performed, as physical (p = 0.0273), emotional (p = 0.0078), and functional subgroups were all significantly reduced (p = 0.0117). Autophony was also significantly reduced following intervention (p = 0.0312). Overall quality of life was seen to be improved following surgery as measured by the Glasgow Benefit Inventory (p = 0.0345). CONCLUSION: Our data suggest that transmastoid plugging of a dehiscence in the superior semicircular canal is a safe and effective means of improving autophony, dizziness and overall quality of life in these patients. We believe that these results should be taken into consideration in discussions regarding surgical approach for patients who are contemplating this procedure.

Surgical anatomy of the facial nerve: from middle cranial fossa approach to endoscopic approach. A pictorial review.

PURPOSE: The pathology of the facial nerve is extremely varied and extensive knowledge of the surgical anatomy in different approaches is required to manage it. During the last 15 years, the development of endoscopic ear surgery has significantly changed anatomical concepts, introducing new surgical approaches. The aim of this review is to illustrate five different surgical approaches to the facial nerve: the endoscopic approach, the middle cranial fossa approach, two translabyrinthine approaches (one simple and one endoscopic-assisted) with decompression of the whole petrous portion of the facial nerve, and a transotic approach with temporal craniotomy. METHODS: Representative cases of middle and/or inner ear pathologies, surgically treated at our ENT Department, were selected to illustrate each of the five different approaches involving the facial nerve throughout its course. RESULTS: In all cases, the pathology was removed with effective decompression of the facial nerve. The surgical anatomy in each surgical approach is described and illustrated. CONCLUSIONS: Facial nerve surgery is challenging for ENT specialists. An excellent knowledge of facial nerve anatomy is needed to eradicate pathology, avoiding nerve injuries and providing a good outcome after surgery.

Transjugular transsigmoid approach for triple dumbbell-shaped jugular foramen schwannomas.

BACKGROUND: Jugular foramen tumors, particularly those that are triple dumbbell-shaped with intracranial, intraforaminal, and extracranial extensions, are difficult to access surgically. However, advances in neuroimaging, neuromonitoring, and skull base surgery have enabled their safe resection with lower rates of morbidity and mortality. METHOD: We share our experience with the surgical technique for the management of triple dumbbell-shaped jugular foramen schwannomas. CONCLUSION: The infralabyrinthine transjugular transsigmoid approach with high cervical exposure under continuous vagus nerve monitoring enables gross total resection of triple dumbbell-shaped jugular foramen schwannomas, aiming at surgical cure of these benign tumors for appropriately selected patients.

Surgical management of pulsatile tinnitus secondary to jugular bulb or sigmoid sinus diverticulum with review of literature.

INTRODUCTION: Jugular bulb and sigmoid sinus anomalies are well-known causes of vascular pulsatile tinnitus. Common anomalies reported in the literature include high-riding and/or dehiscent jugular bulb, and sigmoid sinus dehiscence. However, cases of pulsatile tinnitus due to diverticulosis of the jugular bulb or sigmoid sinus are less commonly encountered, with the best management option yet to be established. In particular, reports on surgical management of pulsatile tinnitus caused by jugular bulb diverticulum have been lacking in the literature. OBJECTIVES: To report two cases of pulsatile tinnitus with jugular bulb and/or sigmoid sinus diverticulum, and their management strategies and outcomes. In this series, we describe the first reported successful case of pulsatile tinnitus due to jugular bulb diverticulum that was surgically-treated. SUBJECTS AND METHODS: Two patients diagnosed with either jugular bulb and/or sigmoid sinus diverticulum, who had presented to the Otolaryngology clinic with pulsatile tinnitus between 2016 and 2017, were studied. Demographic and clinical data were obtained, including their management details and clinical outcomes. RESULTS: Two cases (one with jugular bulb diverticulum and one with both sigmoid sinus and jugular bulb diverticula) underwent surgical intervention, and both had immediate resolution of pulsatile tinnitus post-operatively. This was sustained at subsequent follow-up visits at the outpatient clinic, and there were no major complications encountered for both cases intra- and post-operatively. CONCLUSION: Transmastoid reconstruction/resurfacing of jugular bulb and sigmoid sinus diverticulum with/without obliteration of the diverticulum is a safe and effective approach in the management of bothersome pulsatile tinnitus arising from these causes.

Corticospinal excitability of the biceps brachii is shoulder position dependent.

The purpose of this study was to examine the effect of shoulder position on corticospinal excitability (CSE) of the biceps brachii during rest and a 10% maximal voluntary contraction (MVC). Participants (n = 9) completed two experimental sessions with four conditions: 1) rest, 0° shoulder flexion; 2) 10% MVC, 0° shoulder flexion; 3) rest, 90° shoulder flexion; and 4) 10% MVC, 90° shoulder flexion. Transcranial magnetic, transmastoid electrical, and Erb's point stimulation were used to induce motor-evoked potentials (MEPs), cervicomedullary MEPs (CMEPs), and maximal muscle compound potentials (Mmax), respectively, in the biceps brachii in each condition. At rest, MEP, CMEP, and Mmax amplitudes increased (P < 0.01) by 509.7 ± 118.3%, 113.3 ± 28.3%, and 155.1 ± 47.9%, respectively, at 90° compared with 0°. At 10% MVC, MEP amplitudes did not differ (P = 0.08), but CMEP and Mmax amplitudes increased (P < 0.05) by 32.3 ± 10.5% and 127.9 ± 26.1%, respectively, at 90° compared with 0°. MEP/Mmax increased (P < 0.01) by 224.0 ± 99.1% at rest and decreased (P < 0.05) by 51.3 ± 6.7% at 10% MVC at 90° compared with 0°. CMEP/Mmax was not different (P = 0.22) at rest but decreased (P < 0.01) at 10% MVC by 33.6 ± 6.1% at 90° compared with 0°. EMG increased (P < 0.001) by 8.3 ± 2.0% at rest and decreased (P < 0.001) by 21.4 ± 4.4% at 10% MVC at 90° compared with 0°. In conclusion, CSE of the biceps brachii was dependent on shoulder position, and the pattern of change was altered within the state in which it was measured. The position-dependent changes in Mmax amplitude, EMG, and CSE itself all contribute to the overall change in CSE of the biceps brachii.NEW & NOTEWORTHY We demonstrate that when the shoulder is placed into two common positions for determining elbow flexor force and activation, corticospinal excitability (CSE) of the biceps brachii is both shoulder position and state dependent. At rest, when the shoulder is flexed from 0° to 90°, supraspinal factors predominantly alter CSE, whereas during a slight contraction, spinal factors predominantly alter CSE. Finally, the normalization techniques frequently used by researchers to investigate CSE may under- and overestimate CSE when shoulder position is changed.

CT pre-operative planning of a new semi-implantable bone conduction hearing device.

PURPOSE: Accommodating a novel semi-implantable bone conduction hearing device within the temporal bone presents challenges for surgical planning. This study describes the utility of CT in pre-operative assessment of such an implant. METHODS: Retrospective review of pre-operative CT, clinical and surgical records of 16 adults considered for device implantation. Radiological suitability was assessed on CT using 3D simulation software. Antero-posterior (AP) dimensions of the mastoid bone and minimum skull thickness were measured. CT planning results were correlated with operative records. RESULTS: Eight and five candidates were suitable for device placement in the transmastoid and retrosigmoid positions, respectively, and three were radiologically unsuitable. The mean AP diameter of the mastoid cavity was 14.6 mm for the transmastoid group and 4.6 mm for the retrosigmoid group (p < 0.05). Contracted mastoid and/or prior surgery were predisposing factors for unsuitability. Four transmastoid and five retrosigmoid positions required sigmoid sinus/dural depression and/or use of lifts due to insufficient bone capacity. CONCLUSION: A high proportion of patients being considered have contracted or operated mastoids, which reduces the feasibility of the transmastoid approach. This finding combined with the complex temporal bone geometry illustrates the importance of careful CT evaluation using 3D software for precise device simulation. KEY POINTS: • Preoperative temporal bone CT is essential for determining Bonebridge device suitability. • Mastoid under-pneumatisation and prior mastoidectomy predict a retrosigmoid Bonebridge position. • 3D simulation software is recommended for precise device positioning.

Differences in corticospinal excitability to the biceps brachii between arm cycling and tonic contraction are not evident at the immediate onset of movement.

This is the first study to examine changes in corticospinal excitability to the biceps brachii during the onset of arm cycling from a resting position to a point when steady-state arm cycling was obtained. Supraspinal and spinal excitability were assessed using motor-evoked potentials (MEPs) elicited via transcranial magnetic stimulation and cervicomedullary evoked potentials (CMEPs) elicited via transmastoid electrical stimulation, respectively. Evoked responses were recorded from the biceps brachii during elbow flexion (6 o'clock relative to a clock face) for both arm cycling and an intensity-matched tonic contraction at three separate periods: (1) immediately at the onset of motor output and after completion of the (2) 4th revolution and (3) 9th revolution. There was no difference during initiation between tasks for MEP (P = 0.79) or CMEP amplitudes (P = 0.57). However, MEP amplitudes were significantly larger during arm cycling than an intensity-matched tonic contraction after the completion of the 4th (Cycling 76.48 ± 17.35 % of M max, Tonic 63.45 ± 18.45 % of M max, P < 0.05) and 9th revolutions (Cycling 72.37 ± 15.96 % of M max, Tonic 58.1 ± 24.23 % of M max, P < 0.05). There were no differences between conditions in CMEP amplitudes at the 4th (Cycling 49.6 ± 25.4 % of M max, Tonic 41.6 ± 11.2 % of M max, P = 0.31) or the 9th revolution (Cycling 47.2 ± 17.0 % of M max, Tonic 40.8 ± 13.6 % of M max, P = 0.29). These results demonstrate that corticospinal excitability is not different between arm cycling and a tonic contraction at motor output onset, but supraspinal excitability is enhanced during steady-state arm cycling. This suggests a similarity in the way the corticospinal tract initiates motor outputs in humans, regardless of the differences that present themselves in the later, steady-state stages.

Motoneuron responsiveness to corticospinal tract stimulation during the silent period induced by transcranial magnetic stimulation.

Based on H-reflex data, spinal mechanisms are proposed to be responsible for the first 50-80 ms of the transcranial magnetic stimulation (TMS)-induced silent period. As several methodological issues can compromise H-reflex validity as a measure of motoneuron excitability, this study used transmastoid stimulation to elicit cervicomedullary motor evoked potentials (CMEPs) during the silent period. Eleven subjects made 1-3 visits which involved 32 or 44 brief (~3 s) isometric elbow flexor contractions at 25 % of maximal torque. During each contraction, transmastoid stimulation was delivered in isolation to elicit an unconditioned CMEP and at interstimulus intervals (ISIs) ranging from 50 to 150 ms after TMS to elicit a conditioned CMEP. Stimulus intensities for TMS and transmastoid stimulation were set to elicit a silent period of ~200 ms and an unconditioned CMEP of 15, 50, or 85 % of the maximal compound muscle action potential (M max), respectively. At all ISIs and intensities of transmastoid stimulation, the conditioned CMEP was significantly smaller than the unconditioned CMEP (p < 0.001). However, suppression of the conditioned CMEP was significantly less at 85 % compared to 15 or 50 % M max (p = 0.001). Contrary to published H-reflex data, the conditioned CMEP did not recover within 50-80 ms, remaining significantly suppressed at the longest ISI tested (150 ms). These data suggest the spinal portion of the TMS-evoked silent period is considerably longer than reported previously. Transmastoid stimulation, unlike peripheral nerve stimulation, does not impact proprioceptive inflow to motoneurons. Hence, relative to the H-reflex, the CMEP will be subjected to greater afferent-mediated disfacilitation and inhibition due to the TMS-induced muscle twitch.