Radiologic evaluation of the mastoid segment of the facial nerve tract in the intact temporal bone.

PURPOSE: To localize the facial nerve course in the mastoid segment and to measure its distances relative to the tympanic membrane. METHODS: This is a cross-sectional descriptive study. During 2019 in a tertiary hospital, 129 non-contrast and non-pathologic temporal CT images were studied in a tertiary hospital. Facial nerve distances were measured from the planes passing through the annulus in the axial cross-sections at superior, umbo, and inferior levels of the tympanic membrane. It was done in two different dimensions which are anteroposterior (toward the plane of the ear canal wall) and mediolateral (toward the plane of the tympanic membrane). RESULTS: The least mean anteroposterior distance between the facial nerve and the posterior ear canal wall was at the level of umbo (3.66 ± 0.76 mm). The nearest point of the nerve toward the tympanic membrane was the inferior level (- 0.03 ± 0.81 mm). Overall external ear canal lengths were statistically significantly lower in women rather than men. There was a reverse correlation between the age and the ear canal length. CONCLUSION: Posterior canalplasty seems to be safe unless dissection does not cross the plane of annulus. In this study, the safe margin was 1.4 mm in posterior canal wall drilling. It also should be performed carefully if it extends to the inferior side of the canal. Measuring the mediolateral dimension of the nerve toward the annulus in the axial CT images seems to be practically beneficial, especially in the inferior where the ear canal wall turns and might not act as a good landmark. Paying attention to this plane may reduce the risks of nerve injury in any procedures with transcanal approaches, particularly in inferior canaloplasty.

Tympanic-mastoid and parotid schwannomas of the facial nerve: clinical presentation related to the anatomic site of origin.

Objective: To describe the clinical presentation of the facial nerve schwannomas according to the anatomical site of origin. Method: A retrospective study in which the clinical presentation, diagnostic protocol and treatment of facial nerve tumors in adults was evaluated. Results: We found 6 cases, 4 cases of tympanic-mastoid location at the spectrum of its possible clinical presentation: from symptomatic cases with facial paralysis, to an asymptomatic case in the tympanic portion found as intraoperative finding; and also found two cases located at the parotid gland, one with complete facial paralysis and one without facial palsy. Conclusions: For the diagnosis of intratemporal and parotid schwannomas of the facial nerve, a high clinical suspicion is required given its heterogeneous presentation; its clinical course depends on the segment of origin and expansion: more frequently asymptomatic at the tympanic horizontal portion and symptomatic at the mastoid vertical portion. These tumors must be assessed with imaging studies, incisional biopsy is not recommended. The treatment is surgical resection in symptomatic patients with facial paralysis greater than grade III of House-Brackmann, with immediate reconstruction of the nerve.

Objetivo: Describir la presentación clínica de los schwannomas del nervio facial de acuerdo con el sitio anatómico de origen. Método: Se realizó un estudio retrospectivo en el que se evaluó la presentación clínica, el protocolo diagnóstico y el tratamiento de tumores del nervio facial en adultos. Resultados: Se encontraron seis casos, cuatro de ellos de localización tímpano-mastoidea en los extremos de su posible presentación clínica: desde casos sintomáticos con parálisis facial, hasta un caso asintomático de la porción timpánica encontrado como hallazgo transoperatorio; y se encontraron dos casos de localización parotídea, uno con parálisis facial completa y otro sin parálisis facial. Conclusiones: Para el diagnóstico de tumores intratemporales y parotídeos del nervio facial se requiere una elevada sospecha clínica dado lo heterogéneo de su presentación; su curso clínico depende del segmento de origen y de su extensión: más frecuentemente son asintomáticos los de la porción timpánica y son sintomáticos los de la porción mastoidea. Estos tumores deben evaluarse con estudios de imagen; no se recomienda realizar biopsia incisional. El tratamiento es la resección quirúrgica en los casos sintomáticos con parálisis facial de grado IV o mayor de House-Brackmann, con reconstrucción inmediata del nervio.

Anatomical assessment of the digastric branch of the facial nerve as a landmark to localize the extratemporal facial nerve trunk.

PURPOSE: Localization of the facial nerve trunk (FNT) [i.e., the portion of the facial nerve between the stylomastoid foramen (SMF) and pes anserinus] may be required during various surgical interventions such as parotidectomy and hypoglossal-facial anastomosis. Several landmarks have been proposed for efficient identification of the FNT. We sought to assess the anatomical features of the digastric branch of the facial nerve (DBFN) and its potential as a landmark to identify FNT. METHODS: Fifteen sides of eight cadaveric heads were dissected to find the DBFN. Anatomic features of DBFN including its point of origin relative to SMF, length, and important relationships, as well as the distance between the insertion point on the digastric muscle and mastoid tip were recorded. RESULTS: DBFN was found in all specimens originating from the FNT outside the SMF with an average length (± standard deviation) of 15.4 ± 3.4 mm. In all specimens, the DBFN inserted on the superomedial aspect of the posterior belly of the digastric muscle (PBD). In 8/15 specimens, DBFN was accompanied by the stylomastoid artery on its anteromedial side. Average distance (± standard deviation) between the mastoid tip and the nerve insertion point on PBD was 13.6 ± 2.0 mm (range 10-17). CONCLUSIONS: The DBFN is a reliable landmark for identifying the FNT. It could be consistently identified within 15-20 mm of the mastoid tip on the superomedial aspect of the PBD. The DBFN may be used as a supplementary landmark for efficient localization of the FNT. LEVEL OF EVIDENCE: Not applicable (anatomic study).

The anatomical and radiological evaluation of the Vidian canal on cone-beam computed tomography images.

INTRODUCTION: The aim of this study is to explore the anatomy of the Vidian nerve to elucidate the appropriate surgical approach based on preoperative cone-beam computed tomography (CBCT) images. MATERIALS AND METHODS: The Vidian canal and its surrounding structures were morphometrically evaluated retrospectively in CBCT images of 400 cases by the Planmeca Romexis program. The types of the Vidian canal were determined and seven parameters were measured from the images. RESULTS: Three types of the Vidian canal according to the relationship with the sphenoid bone were found as follows: the Vidian canal totally protruded into the sphenoid sinus (19.75%), partially protruded into sphenoid sinus (44.37%) and embedded inside bony tissue of the body of sphenoid bone (35.87%). The position of the Vidian canal was medial (34.62%), on the same line (55.12%) and lateral (10.25%) to the medial plate of the pterygoid process. The distance between the Vidian canal and the vomerine crest, the mid-sagittal plane, the round foramen, the palatovaginal canal, and the superior wall of the sphenoid sinus, the length of the Vidian canal and the angle between the Vidian canal and the sagittal plane was found to be 16.69 ± 2.14, 13.80 ± 2.00, 8.88 ± 1.60, 5.83 ± 1.37, 23.98 ± 2.68, 13.29 ± 1.71 mm and 25.78° ± 3.68° in males, 14.62 ± 1.66, 11.43 ± 1.28, 8.51 ± 1.63, 5.78 ± 0.57, 22.37 ± 2.07, 12.91 ± 1.26 mm and 23.43° ± 3.07° in females, respectively. CONCLUSIONS: Our results may assist with proper treatment for surgical procedures around the Vidian canal with a high success rate and minimal complications. Therefore, the results obtained in this study contribute to the literature.

Anterior Greater Auricular Point: Novel Anatomic Landmark to Facilitate Harvesting of the Greater Auricular Nerve.

BACKGROUND: The greater auricular nerve (GAN) may be used as a nerve graft during neurosurgical procedures to repair damaged nerves. There is extensive literature on localization of the GAN at the posterior triangle of the neck, but objective information on localization of the GAN at the anterior triangle of the neck close to cranial neurosurgical fields is lacking. The aim of this study was to introduce simple and reliable landmarks to localize the GAN at the anterior triangle of the neck to facilitate its harvest during neurosurgical procedures. METHODS: The GAN was exposed bilaterally in 11 cadaveric specimens at the point of crossing the anterior border of the sternocleidomastoid muscle (anterior greater auricular point [AGA]). Distances from the AGA point to the angle of the mandible and the tip of the mastoid process were measured. Additionally, the location of the crossing point between the GAN and an imaginary line passing through the mastoid tip and the angle of the mandible (M-A line) was found relative to these bony landmarks. RESULTS: Mean (±SD) distances from the AGA point to the mastoid tip and the angle of the mandible were 29.1 ± 3.4 mm and 27.5 ± 4.5 mm, respectively. The GAN was always found to cross the M-A line in its middle third (mean 48.2% ± 6.9% from the mastoid tip). CONCLUSIONS: The AGA point and the M-A line are reliable landmarks for locating the GAN at the anterior triangle of the neck and for helping neurosurgeons expose and harvest the GAN efficiently.

Topographic anatomy of the great auricular point: landmarks for its localization and classification.

PURPOSE: The great auricular point (GAP) marks the exit of the great auricular nerve at the posterior border of the sternocleidomastoid muscle (SCM). It is a key landmark for the identification of the spinal accessory nerve, and its intraoperative localization is vital to avoid neurological sequelae. This study delineates the topography and surface anatomy landmarks that used to localize the GAP. METHODS: Thirty cadaveric heminecks were dissected on a layer-by-layer approach. The topography of the GAP was examined relative to the insertion point of the SCM at the clavicle, tip of the mastoid process, and angle of the mandible. The GAP and its relation to the SCM were determined as a ratio of the total length of the SCM. RESULTS: The GAP was demonstrated to be in a predictable location. The mean length of the SCM was 131.4 ± 22 mm, and the mean distance between the GAP and the mastoid process was found to be 60.4 ± 13.76 mm. The ratio of the GAP location to the total SCM length ranged between 0.33-0.57. The mean distance between the angle of the mandible and the GAP was determined to be 57 ± 22.2 mm. Based on the midpoint of the SCM, the GAP was above it in 66.7 % of subjects and classified to Type A, and below it in 33.3 % of subjects appointed to Type B. CONCLUSIONS: The anatomical landmarks utilized in this study are helpful in predicting the location of the GAP relative to the midpoint of the SCM and can reduce neural injuries within the posterior triangle of the neck.

Implanting straight into cochlea risks the facial nerve: a Cartesian coordinate study.

PURPOSE: To describe the straight-into-cochlea line that affords the best access for an electrode array to enter via the round window, and how this line relates to the facial nerve, the incus, and mastoid size. The straight-into-cochlea line is important to minimize the cochlear trauma and maximize the likelihood of placement into the scala tympani. METHODS: High-resolution CT scans were obtained for ten craniums with the extremes of large (N = 5) and small (N = 5) mastoid pneumatization; the specimens were from a series of 41 ear normal craniums. Using FIJI, a publicly available software program, the straight-into-cochlea insertion line was determined by defining the x-y-z coordinates of the middle of the round window and a point 6.0 mm into the cochlea on its centrifugal wall. Then, from the extended straight-into-cochlea insertion line, we determined the shortest perpendicular distance to the middle of the fallopian canal, and from that "fallopian point" to the apex of the posterior process of the incus. RESULTS: We found good repeatability of measurements. We found the extended straight-into-cochlea insertion lines routinely close to or in the midst of the fallopian canal (50 % ≤ 1.0 mm). We found the lines 4.7-7.8 mm from the apex of the posterior process of the incus. Line positions relative to "fallopian point" and incus showed no relation to mastoid pneumatization. For the distance "fallopian point" to incus, bilateral symmetry was suggested. CONCLUSIONS: Using landmarks registered in an x-y-z coordinate system, straight-into-cochlea insertion via the round window puts the facial nerve at risk.

Surgical anatomy of facial nerve for revision transmastoid surgery.

We analyze the relationships of the 3 segments of the facial nerve with respect to constant anatomic structures that can be identified during revision surgery via translabyrinthine approach. This study was conducted on 15 formalin-fixed cadavers whose facial nerves were dissected bilaterally under operative microscope via translabyrinthine approach. The distances between the round window niche and the midpoint of the tympanic segment and the beginning of the mastoid segment were 6.64 ± 1.79 mm and 3.99 ± 0.79 mm, respectively. The distances between the tympanic ostium of the eustachian tube and the first and the second genu were 7.02 ± 0.62 mm and 12.25 ± 1.24 mm, respectively. We used the superior semicircular canal, the tympanic ostium of the eustachian tube, and the round window niche as landmarks to identify the facial nerve during revision surgery. Our study also showed that the auricular branch may also be originated from the posterior surface of the facial nerve.

Measurement and analysis of facial nerve on fully displayed multislice computed tomographic multiplanar reconstruction image.

The objectives of this study were to measure the length of horizontal segment of facial nerve (HFN), the length of vertical segment of facial nerve (VFN), and the angle between these 2 segments on a fully displayed multislice computed tomographic multiplanar reconstruction (MPR) images of HFN and VFN and to analyze the data with respects to side, sex, and age. Parameters of 234 patients (468 observations, 118 men and 116 women, aged 4-70 years) with intact temporal bone were measured on multislice computed tomographic multiplanar reconstruction images. The data gained were analyzed by statistical method. The left and right lengths of VFN were significantly different (P < 0.05). And the length of HFN, the length of VFN, and the angle between males and females were significantly different (P < 0.05). We divided the data into 3 groups to study correlations between measurements and age. In underaged group, there was a strong positive correlation between the length of VFN and age; the value of Pearson correlation was 0.645. And there was a weak correlation between the angle and the age; the value of Pearson correlation was 0.270. In older-aged group, there was a moderate negative correlation between the length of VFN and age; the value of Pearson correlation was -0.408. Our results are of high potential to expand the visual field to facial nerve and may provide more detailed information to surgeries of facial nerve, middle ear, and temporal bone.

A new technique to investigate vestibulo-spinal reflexes.

Vestibulospinal reflexes can be elicited in humans by low amplitudes direct (galvanic) currents lasting tens of milliseconds and applied across the two mastoids bones, which can be delivered by particular stimulators. The stimulus induces a perception of body sway and a postural response appropriate to counteract the perceived sway. Both the direction of the perceived and induced body sway are modulated by the orientation of the head with respect to the body. This phenomenon is due to the fact that integration of vestibular and neck signals allows to correctly infer the direction of body sway from the labyrinthine input, which is instead related to direction of head motion. The modulation of stimulus-elicited body sway by neck rotation could be utilised for testing the effectiveness of neck proprioceptive signals in modifying the reference frame for labyrinthine signals from the head to the body. In the present experiments we showed that labyrinthine stimulation can be performed also by using train of pulses of 1 msec duration, which can be delivered by virtually all stimulators allowed for human use. Moreover, we developed a simple technique for visualising the time course of the changes in the direction of the postural response, based on the evaluation of the velocity vector of subject's centre of pressure. This method could be exploited in order to the test the efficacy of neck proprioceptive information in modifying the reference frame for processing vestibular signals in both physiological and pathological condition.

Vestibular neuritis has selective effects on air- and bone-conducted cervical and ocular vestibular evoked myogenic potentials.

OBJECTIVE: To characterise the changes in cervical (cVEMP) and ocular (oVEMP) vestibular evoked myogenic potentials to different stimuli in patients with vestibular neuritis (VN). METHODS: cVEMPs and oVEMPs were recorded using air-conducted (AC; clicks and short tone bursts) and bone-conducted (BC; lateral impulses and taps) stimuli in VN patients (n=23) and normals (n=40). RESULTS: AC evoked cVEMPs revealed few abnormalities, significantly less than for AC evoked oVEMPs (cVEMP: 22% vs oVEMP: 68%, P<0.001). Lateral impulses showed high rates of abnormalities (74% vs 70%, P>0.05) for both reflexes. Although forehead taps produced low rates of abnormalities for both reflexes (33% vs 13%, P>0.05), response amplitudes were smaller from the affected ear (P<0.05). CONCLUSIONS: AC stimuli were associated with low abnormality rates of cVEMPs, consistent with sparing of inferior nerve function in VN, but frequent abnormalities of oVEMPs. The high rates of abnormalities shown for lateral impulses suggest a dependence on superior nerve (i.e. utricular) afferents for both oVEMPs and cVEMPs. SIGNIFICANCE: Lateral impulses behave as expected for utricular function and AC cVEMPs for saccular function. The AC evoked oVEMP seems to depend on the integrity of the superior vestibular nerve, possibly due to saccular afferents travelling in it.

[Relationship between 3-d reconstruction of regenerated fibers and functional recovery after mastoid segment of facial nerve was repaired].

OBJECTIVE: To explore the relationship between three-dimensional (3-D) reconstruction of regenerated fibers and functional recovery after mastoid segment of facial nerve was repaired with either end-to-end anastomosis or autogenous great auricular nerve grafting. METHOD: Thirty healthy adult New Zealand white rabbits were randomly divided into two groups: one was end-to-end anastomosis group and another was autogenous great auricular nerve grafting group. Only mastoid segment of right facial nerve of each animal was dissected and the contralateral nerve was as a control. Electromyogram (EMG) were recorded from 5 animals of each group at the 30th d, 90th d and 120th d after operation. After that the nerves were extracted, fixed, decalcified and embedded in paraffin. Samples was sectioned serially at 6 microm and stained with special trichrome stain. All the imagines were imported into Mimics software to reconstruct the 3-D model. RESULT: The significant differences were found in the regenerate fibers on 30 th d,and were found in amplitude of EMG on 30 th d and 90 th d. The image of 3-D reconstruction showed that the myelin sheath were thickening, connected from proximal to the distal gradually after repair. CONCLUSION: The 3-D reconstruction of regenerated nerve fibers partly conformed to the functional recovery after facial nerve trunk was repaired. The functional recovery of facial nerve was related with both the quantity and the quality of regenerated nerve fibers.

Intratemporal course of the facial nerve: morphological, topographic and morphometric features.

The purpose of this study is to present some morphological and morphometric aspects of the facial nerve and especially of the tympanic and mastoid segments of this nerve. The authors follow up a mesoscopic study concerning the tract (length, angulation, width) of these segments and the anatomic relations with the important structures of the middle ear. At the same time, some anatomical variations which involve the canal of the facial nerve (dehiscences, tract deviation or other anatomical deviations) are presented. To evaluate the risk of the facial nerve injury during operations for chronic otitis media with or without cholesteatoma, stapedectomy in otosclerosis, exploratory tympanotomy, tympanoplasty, canaloplasty, osteomas surgery or other otologic surgery that involve facial nerve area. The intricate course of the facial nerve through the temporal bone is of vital concern to all otologic surgeons, since it often traverses the surgical field. Therefore, authors will review the course of the facial canal through the petrosal portion of the temporal bone from the internal auditory meatus to the stylomastoid foramen, paying particular attention to its relations to adjacent structures.

Occipital nerve stimulator placement via a retromastoid to infraclavicular approach: a technical report.

Occipital nerve stimulation is a form of peripheral nerve stimulation used to treat refractory headache disorders. Various techniques have been described for occipital nerve stimulator implantation; these include midline cervical or retromastoid lead insertion with internal pulse generator placement in the infraclavicular, gluteal or low abdominal regions. Lead migration is one of the most common complications of occipital nerve stimulators. Implantation approaches that include remote battery sites may contribute to mechanical stress on the components, as the leads or extensions may traverse highly mobile body regions. In this technical report, we describe an occipital stimulator implantation technique that may be advantageous in terms of patient positioning, ease of surgical approach and minimization of mechanical stress on components.

Chondromyxoid fibroma of the mastoid facial nerve canal mimicking a facial nerve schwannoma.

Chondromyxoid fibroma of the skull base is a rare entity. Involvement of the temporal bone is particularly rare. We present an unusual case of progressive facial nerve paralysis with imaging and clinical findings most suggestive of a facial nerve schwannoma. The lesion was tubular in appearance, expanded the mastoid facial nerve canal, protruded out of the stylomastoid foramen, and enhanced homogeneously. The only unusual imaging feature was minor calcification within the tumor. Surgery revealed an irregular, cystic lesion. Pathology diagnosed a chondromyxoid fibroma involving the mastoid portion of the facial nerve canal, destroying the facial nerve.

Vulnerable structures during intraoral sagittal split ramus osteotomy.

The aim of this study was to elucidate the anatomical structures that are vulnerable to injury during sagittal split ramus osteotomy (SSRO). Twenty-nine hemifaces of 19 Korean adult cadavers (11 men and 8 women; age range, 50-91 years) were dissected, and the locations of the facial nerve, retromandibular vein (RMV), and external carotid artery (ECA) were measured on the base of the mandibular posterior border and occlusal plane. Sagittal split ramus osteotomy was performed on the cadaver heads at intervals of 10 mm, and the proximity of the facial nerve was observed. The buccal branch and mandibular branch crossed the posterior border of the mandible (PBM). Most buccal branches (86%) crossed between 7/10 and 10/10 of the distance from gonion to mandibular notch (MN). Most mandibular branches (86%) were between 6/10 and 1/10 of the distance from gonion to MN. Most facial nerve trunks (FNTs) (82%) were within a circle of 9 mm in radius. Its center was located 34 mm posterior and 7 mm inferior to the MN. The FNT was located in the range of 11 to 14 mm medial to the PBM. The FNT emerged out of the stylomastoid foramen and ran anteroinferiorly in a direction of 45 degrees. In 10-mm ramus setback osteotomy, FNT was very close to the PBM, running almost vertically. Retromandibular vein was 5.5 to 8.6 mm posterior and 4.2 to 9.1 mm medial to the PBM. The ECA was located at 5.7 to 6.5 mm posterior and 10.5 to 12.9 mm medial to PBM. Facial nerve could be averted from injury by doing less setback. Bleeding after SSRO is likely to be due to the injury of RMV which is closer to the PBM (4-9 mm) than ECA (12-13 mm).

Auditory evoked responses in the rat: transverse mastoid needle electrodes register before cochlear nucleus and do not reflect later inferior colliculus activity.

A previously described technique putatively differentiates short-latency auditory evoked potentials in peripheral and central neural pathways of the mouse and rat [Galbraith G, Waschek J, Armstrong B, Edmond J, Lopez I, Liu W, et al. Murine auditory brainstem evoked response: putative two-channel differentiation of peripheral and central neural pathways. J Neurosci Methods 2006;153:214-20]. This technique involves recording from orthogonally oriented subdermal needle electrode pairs, using fast sample rates (100k/s) to accurately measure differences in neural timing and waveform morphology. Electrodes oriented in a transverse plane (mastoid-to-mastoid) register an initial positive-going peak earlier than peaks recorded from electrodes oriented along the scalp midline (anterior and posterior to the interaural line). The absolute latency of the early mastoid component is consistent with an origin in the primary auditory nerve, while delayed midline latencies implicate activity in central neural pathways. We report here the results of recording simultaneously from transverse mastoid (M) needle electrodes and electrodes acutely implanted in cochlear nucleus (CN) and inferior colliculus (IC). The results show a highly consistent pattern in which the initial mastoid component leads CN by an average of 0.16 ms, suggesting an obligatory neural site of origin of the mastoid response that is distal to IC, namely the auditory nerve. Moreover, later IC components (beyond approximately 3.5 ms) are completely absent in mastoid recordings, indicating that the transverse mastoid recordings provide a relatively isolated measure of early auditory neural activity.

Sound-evoked myogenic potentials on the sternocleidomastoid muscle in monkeys.

CONCLUSION: We recorded sound-evoked myogenic potentials of the sternocleidomastoid (SCM) muscle using awake monkeys. The characteristics of these potentials are similar to those of vestibular evoked myogenic potentials (VEMPs) in humans, suggesting that the sound-evoked myogenic potentials of the SCM muscle in monkeys may be utilized as an animal model of VEMPs. OBJECTIVE: The pathway of the VEMPs remains uncertain as no animal model has yet been used to record sound-evoked myogenic potentials in the SCM muscle. Therefore, the present study aimed to establish an animal model of VEMPs using macaque monkeys. MATERIALS AND METHODS: Four macaque monkeys were used. A pair of electrodes was attached on the SCM muscle ipsilateral side to the intense sound stimulation. RESULTS: The sound-evoked myogenic potentials of the SCM muscle exhibited a biphasic waveform. When a click at 125 dBSPL was applied, the peak latency of the first positive wave was 12.5 ms and was not delayed when the stimulating sound intensity was reduced. The thresholds of the myogenic potentials were 103 dBSPL, which were 43 dB higher than those of the auditory brainstem response (ABR). When a short tone burst was applied, the reactive optimal frequency of the myogenic potentials was relatively low (500-1000 Hz).