Continuous electrical stimulation of superior laryngeal nerve inhibits initiation of swallowing in anesthetized rats

Pharyngeal electrical stimulation (PES) applies electrical stimulation to pharyngeal mucosa (PhM) and represents a useful approach to improve swallowing function in patients with dysphagia. To determine the optimal PES modality to treat dysphagia, the mechanism underlying the effects of PES on swallowing function must be elucidated. In this study, we evaluated how PES and electrical stimulation of the superior laryngeal nerve (SLN) modulate the initiation of swallowing in anesthetized rats. A swallow was evoked by electrical stimulation of the PhM, SLN, and nucleus of the solitary tract (nTS) and pharyngeal mechanical stimulation using a von Frey filament. A swallow was identified by electromyographic bursts in mylohyoid and thyrohyoid muscles. Bilateral SLN transection abolished the swallows evoked by PhM electrical stimulation. PhM and SLN electrical stimulation decreased swallowing frequency in a similar time-dependent manner. Intravenous administration of the GABAA receptor antagonist bicuculine did not affect the time-dependent change in swallowing frequency during SLN electrical stimulation. Continuous SLN electrical stimulation significantly inhibited pharyngeal mechanically and nTS-electrically evoked swallows compared with before and 5 min after stimulation. The present findings suggest that the SLN plays a primary role in PES-evoked swallows. Additionally, continuous SLN electrical stimulation inhibits the initiation of swallowing, and the modulation of central network associated with swallowing might be partially involved in this inhibition.

Modulation of the swallowing reflex by stimulation of the gigantocellular reticular nucleus in the rat

OBJECTIVES

The gigantocellular reticular nucleus (Gi) projects to the nuclues of the solitary tract nucleus (NTS) and the lateral reticular formation (LRF) above the nucleus ambiguus. The swallowing central pattern generator comprises the NTS and the LRF. The present study examined whether stimulation of the Gi affects the swallowing reflex.

METHODS

Experiments were performed on urethane-anesthetized rats. The swallowing reflex was evoked by repetitive electrical stimulation of the superior laryngeal nerve and responses were recorded from the mylohyoid muscle on an electromyogram. The Gi was stimulated electrically. In addition, glutamate was injected into the Gi. The Friedman's test, followed by the Wilcoxon signed-rank test with Bonferroni correction, were used to assess the effects of electrical stimulation of the Gi. The Wilcoxon signed-rank test was used to assess the effects of glutamate injection into the Gi. Differences were considered significant at the P < 0.05 level.

RESULTS

The number of swallows was significantly increased or decreased by electrical stimulation of the Gi or after injection of glutamate into the Gi. In both electrical stimulation of the Gi and injection of glutamate into the Gi, the onset latency of the first swallow was prolonged when the number of swallows was decreased but showed no change when the number of swallows was increased.

CONCLUSIONS

The present results suggest that the Gi is involved in the control of swallowing.

Avoiding Complications of Thyroidectomy: Recurrent Laryngeal Nerve and Superior Laryngeal Nerve Preservation

Both the superior and recurrent laryngeal nerves are at risk for injury during thyroid surgery. Comprehensive preoperative evaluation is key for surgical planning. Exposing nerves through careful dissection is the safest strategy to minimize injury risk. Intraoperative neural monitoring can be beneficial for both identifying and preserving the nerves.

Upper cervical anterior fusion to C2 with temporary infrahyoid muscle detachment: a clinical case series and description of surgical technique

BACKGROUND

Anterior cervical spine surgery to C2 (ACSS-C2) is a challenging procedure that often results in postoperative persistent dysphagia or dyspnea due to injury to the internal branch of the superior laryngeal nerve (iSLN) or the relatively narrow and soft oropharynx. This study aimed to describe the surgical outcomes of our modified approach with temporary infrahyoid muscle detachment during ACSS-C2.

METHODS

Patients who underwent ACSS-C2 at two institutions between June 2015 and January 2022 were prospectively enrolled. Intraoperatively, we performed temporary detachment of the infrahyoid muscle from the hyoid bone to improve laryngeal mobility and accessibility to C2. This procedure also allowed for the easy identification and preservation of the iSLN. We retrospectively investigated the surgery-related complications and outcomes of bony fusion.

RESULTS

Twelve patients were enrolled in this study; five and seven patients underwent single- and multi-level fusion surgery, respectively. Intraoperative preservation of the iSLN and proper visualization of C2 were achieved in all cases. Subsequent decompression and instrumentation were successfully performed. Two older patients (78 and 81 years) who underwent multi-level fusion experienced transient postoperative dysphagia. None of the patients required unplanned reintubation or revision surgery because of instrumentation failure. Solid bony fusion was achieved in all cases.

CONCLUSIONS

Our modified approach with temporary infrahyoid muscle detachment during ACSS-C2 reduces the incidence of postoperative persistent dysphagia and dyspnea. However, in older patients at high risk for postoperative dysphagia, multi-level fusion should be avoided, and alternative procedures should be considered.

Superior laryngeal nerve block for treatment of throat pain and cough following laryngeal herpes zoster: A case report

BACKGROUND

Herpes zoster is caused by reactivation of latent varicella-zoster virus infection within the sensory nerve ganglion of the spinal or cranial nerves. Laryngeal herpes zoster is rare and involves superior laryngeal nerve, which leads to several complications such as throat pain, and cough.

CASE SUMMARY

Patient concerns: A 52-year old woman presented with a 70 d history of throat pain and a 67 d history of non-productive cough. Three days after onset of pain, she was diagnosed with laryngeal herpes zoster. Flexible nasolaryngoscopy revealed multiple white ulcerated lesions on the left hemi epiglottis and the left supraglottic area. She was prescribed with 750 mg famciclovir a day for 7 d, and 150 mg pregabalin, 100 mg tramadol and 10 mg nortriptyline a day for 67 d. However, despite of these medications, she complained of pain and persistent cough. Therefore, superior laryngeal nerve block under ultrasound guidance was performed. Three days after the intervention, the throat pain and cough disappeared. The patient remained symptom-free at 3 mo follow-up.

CONCLUSION

A superior laryngeal nerve block can be an effective option for treatment of pain and cough following laryngeal herpes zoster.

Surgical landmarks for identification and preservation of the internal branch of the superior laryngeal nerve

OBJECTIVE

To determine the topographical anatomic features of the internal branch of the superior laryngeal nerve (ibSLN) at the thyrohyoid membrane entrance area in relation to certain consistent anatomical structures.

MATERIALS

METHODS: Twenty-two fresh adult head cadavers (9 male, 13 female; age range 52-95 years) with no signs of abnormality in the neck were dissected to determine the anatomic relationship of ibSLN and superior border of thyroid cartilage, thyroid notch, carotid bifurcation, hyoid corpus, and hyoid greater cornu.

RESULTS

The topographical relationship between ibSLN and superior border of thyroid cartilage, thyroid notch, carotid bifurcation, hyoid corpus, and hyoid greater cornu was identified bilaterally in all cadavers. According to the measures, danger zone and safe zone areas for surgical could be predicted and for surgical manipulations as well.

CONCLUSION

We provided the surgical anatomy and important landmarks for determining the internal branch of superior laryngeal nerve in the thyrohyoid membrane entrance region to avoid surgical damage during surgeries of this region.

Stimulation of the center of the lateral reticular nucleus suppresses the swallowing reflex in rats

Morphological studies have demonstrated that the lateral reticular nucleus (LRt) receives fibers projected from sites that are related to control of the swallowing reflex. Although the LRt may therefore be related to control of the swallowing reflex, the functional role of the LRt in the swallowing reflex remains unknown. The present study examined whether the swallowing reflex is modulated by stimulation of the LRt. These experiments were performed on rats anesthetized by urethane. The swallowing reflex was evoked by repetitive electrical stimulation of the superior laryngeal nerve (SLN) and was identified by electromyographic activities from the mylohyoid muscle. Electrical stimulation was applied to the LRt or glutamate was injected into the LRt. The number of swallows was reduced, and the latency of the onset of the first swallow was increased during electrical stimulation near the middle of the rostrocaudal direction of the LRt. The number of swallows was reduced, and the latency of onset of the first swallow increased after microinjection of glutamate near the rostrocaudal center of the LRt. The present study suggests that the LRt is involved in control of the swallowing reflex.

A Rare Case of Extralaryngeal Schwannoma Arising from the Superior Laryngeal Nerve

Schwannomas are the most common neurogenic tumours arising in the parapharyngeal space. Usually they arise from the vagus nerve but rarely have an extralaryngeal presentation arising from the superior laryngeal nerve. In the case reported here, cytology could not confirm the diagnosis and imaging could not identify the nerve of origin.

Distinct modulation of tracheal and laryngopharyngeal cough via superior laryngeal nerve in cat

Unilateral and bilateral cooling and bilateral transsection of the superior laryngeal nerve (SLN) were employed to modulate mechanically induced tracheobronchial (TB) and laryngopharyngeal (LPh) cough in 12 anesthetized cats. There was little effect of SLN block or cut on TB. Bilateral SLN cooling reduced the number of LPh (<50 %, p < 0.05), amplitudes of diaphragm EMG activity (<55 %, p < 0.05), and cough expiratory efforts (<40 %, p < 0.01) during LPh. Effects after unilateral SLN cooling were less pronounced. Temporal analysis of LPh showed only shortening of diaphragm and abdominal muscles burst overlap in the inspiratory-expiratory transition after unilateral SLN cooling. Bilateral cooling reduced both expiratory phase and total cough cycle duration. There was no significant difference in the average effects of cooling left or right SLN on LPh or TB as well as no differences in contralateral and ipsilateral diaphragm and abdominal EMG amplitudes. Our results show that reduced afferent drive in the SLN markedly attenuates LPh with virtually no effect on TB.

A Case of Carotid Body Tumor with Perineural Tumor Spread along the Superior Laryngeal Nerve

We report a case of a patient with a carotid body tumor with perineural tumor spread along the right superior laryngeal nerve. Perineural spread is most commonly associated with squamous cell, adenoid cystic, and mucoepidermoid carcinoma. To the best of our knowledge, this has not been reported previously with carotid body tumor.

Pathophysiology of aspiration in a unilateral SLN lesion model using quantitative analysis of VFSS

OBJECTIVE

The purpose of this study was to elucidate the pathophysiology of aspiration in previously studied female infant piglets after a unilateral superior laryngeal nerve (uSLN) lesion.

METHODS

Videofluoroscopic swallow studies (VFSS) were acquired from 15 female piglets ages 2-3 weeks (9 with uSLN lesion and 6 controls). VFSS were analyzed at 30 frames/second sampling rate. Quantitative measures were conducted and compared between groups using published methodologies for VFSS assessment in adult and infant humans. Measures included the: 1) number of lingual-palatal contacts (LPC) (i.e. pre-swallow), 2) total pharyngeal transit time (TPT), 3) offset of swallow (offP), as well as onset of: 4) pharyngeal stage (onP), 5) pharyngoesophageal segment opening (oPES), 6) maximum PES opening (maxPES), 7) airway closure onset (oAC), and 8) maximum airway closure (maxAC). Measures 5-7 were determined relative to onP. Bolus residue was rated by severity (0 (none) to 3 (severe)). A gamma regression was used to compare continuous measures between lesioned and control groups.

RESULTS

The number of LPC (p = .006), TPT (p = .023) and timing of maxAC (p = .041) were significantly greater in the uSLN lesion than the control group.

CONCLUSIONS

Outcomes of this study replicated prior published findings and elucidated that piglets with right uSLN lesions exhibited delayed maxAC. Noteworthy was the use of clinically relevant quantitative videofluoroscopic measures in piglets for comparison to future studies in human pediatric populations.

Effects of Superior Laryngeal Nerve Lesion on Kinematics of Swallowing and Airway Protection in an Infant Pig Model

The superior laryngeal nerve provides detailed sensory information from the mucosal surfaces of laryngeal structures superior to the vocal folds, including the valleculae. Injury to this nerve results in airway penetration and aspiration. Furthermore, such injuries might have an impact on the function of multiple structures involved in intraoral transport and swallowing due to connections within the brainstem. We sought to determine the effects of a surgical lesion of the superior laryngeal nerve on kinematics of the tongue, hyoid, and epiglottis during swallowing. We implanted radio-opaque markers into five infant pigs under anesthesia. Then we fed milk mixed with contrast agent to the pigs while they were recorded via video fluoroscopy, before and after a surgery to transect the superior laryngeal nerve. We digitized and rated airway protection in 177 swallows. We found that in most animals, swallow duration was shorter after nerve lesion. The hyoid also traveled a shorter distance after lesion. Frequently, individuals reacted differently to the same nerve lesion. We suggest that these differences are due to individual differences in neurological connections. When comparing hyoid kinematics between swallows with successful or failed airway protection, we found more consistency among individuals. This indicates that protecting the airway requires specific sets of kinematic events to occur, regardless of the neurological differences among individuals.

Surgical treatment of fourth branchial apparatus anomalies: a case series study

Background

Fourth branchial apparatus anomalies, are rare clinical entities, and present as complex cysts, sinuses and fistulae in the neck that can be difficult to manage.

Methods

This is a retrospective review of a series of consecutive patients with fourth branchial apparatus anomalies treated at Department of Otolaryngology Head and Neck Surgery, Beijing Friendship Hospital, Capital Medical University, from Apr 2014 to Nov 2019.

Results

Ten patients with fourth branchial apparatus anomalies were identified, including 8 patients with fourth branchial fistula, and 2 patients with fourth branchial pouch sinus. There were 6 female patients and 4 male patients. Their age was from 6 years old to 39 years old (average age 20.4 years old, median age was 21 years old). All 8 fistulae were on the left side, while 2 pouch sinuses were both on the right side. Pre-operative examination with fiberoptic laryngoscope, barium swallow X-ray, CT or MRI identified internal orifice at pyriform fossa apex in 8 (80%) patients. All patients underwent challenging surgical resection by the senior author. Intra-operative direct laryngoscope confirmed or identified internal orifice in 9 (90%) patients. The tracts were all followed to the vicinity of inferior cornu of the thyroid cartilage and the cricothyroid space. Complete resection of cervical lesions and their attachment to hypopharynx were achieved in 9 cases. No complication occurred. One recurrence was detected, in the only patient whose internal orifice could not be located pre- or intra-operatively, and the hypopharyngeal attachment could not be removed.

Conclusions

Direct laryngoscopy under general anesthesia is a reliable method of diagnosis for the fourth branchial apparatus anomalies. Complete surgical removal of fourth branchial apparatus anomalies, including their hypopharyngeal attachment, is the treatment of choice, and the key to prevent recurrence.

Suppressive effect of the swallowing reflex by stimulation of the pedunculopontine tegmental nucleus

This study investigates whether the swallowing reflex is modulated by stimulation of the pedunculopontine tegmental nucleus (PTg). Sprague-Dawley rats under urethane anesthesia were used. The swallowing reflex was induced by electrical stimulation of the superior laryngeal nerve and was identified by the electromyographic activities from the mylohyoid muscle. The number of swallows was reduced by electrical stimulation of the PTg. The latency of the onset of the first swallow was increased during stimulation of the PTg. The duration of electromyogram bursts of the mylohyoid muscle was significantly shorter during the PTg stimulation than with no stimulation. The number of swallows was reduced, latency of onset of the first swallow increased, the duration of electromyogram bursts of the mylohyoid muscle was significantly shorter and the peak-to-peak amplitude of electromyogram bursts of the mylohyoid muscle was significantly suppressed after microinjection of glutamate into the PTg. These results suggest that the PTg is involved in the control of swallowing.

Strategies for superior thyroid pole dissection in transoral thyroidectomy: a video operative guide

BACKGROUND

The dissection of the superior thyroid gland pole is challenging when using the in TransOral Endoscopic Thyroidectomy Vestibular Approach (TOETVA) due to (a) the cranio-caudal approach, (b) cranial-caudal view, and (c) the restriction of maneuverability inside the narrow neck air pocket.

METHODS

In this paper and operative video guide, a series of TOETVA's tips and tricks are presented with an emphasis on the strategies for a safe approach to the superior thyroid gland pole structures.

RESULTS

Management of the upper thyroid pole structures includes: (a) use of a 5 mm/30°-45° endoscope; (b) retraction ports up to the limit of the lower jaw edge; (c) lateral retraction of 1/3 of the cranial strap muscles; (d) isthmectomy; (e) cutting the sternothyroid muscle cranially for 1 cm; (f) retraction of the thyroid upwards and laterally; (g) monitoring the external branch of the superior laryngeal nerve, and (h) sealing individual vessel branches.

CONCLUSION

Access to the superior thyroid pole space through the TOETVA approach presents some challenges, particularly when accessing thyroid vessels or nodules located or displaced more cranially. Strategies that enhance a critical view of the superior thyroid gland structures can protect them from damage and have the potential to improve the safety of the TOETVA and decrease potential conversion rates.

Superior laryngeal nerve transection for neuropathic cough: A pilot study

OBJECTIVE

To describe a novel surgical therapy for the treatment of medically refractory neuropathic cough, in which carefully selected subjects undergo surgical transection of the internal branch of the superior laryngeal nerve (iSLN).

METHODS

Subjects with a diagnosis of neuropathic cough, who were not improved after two medication trials, underwent iSLN block with local anesthetic in the office. While anesthetized, they underwent provocative testing to determine whether the nerve block improved their symptoms; if so, a modified barium swallow study (MBSS) was performed to determine whether they still swallowed safely without supraglottic sensation. Those who passed this screening were offered operative iSLN transection. We retrospectively reviewed our results to date.

RESULTS

Six subjects (5 females, ages 46-71), with neuropathic cough symptoms for 2-15 years, passed the screening and underwent iSLN transection procedures. At a mean follow-up of 8.2 months, significant symptomatic relief was experienced by 5/6 subjects, with Cough Severity Index (CSI) scores averaging 34.83 ± 6.94 pre-op (range 36-40) and 15.5 ± 11.81 post-op (range 0-29) (p = 0.043). Operative time averaged 49 min (range 30-64). There were no major complications. No subjects experienced post-op aspiration problems.

CONCLUSION

This preliminary data supports iSLN transection as a viable option for subjects with refractory neuropathic cough. Our screening algorithm identifies subjects that would be expected to improve with this procedure and confirms a safe swallow.

Thyroxin and calcitonin secretion into thyroid venous blood is regulated by pharyngeal mechanical stimulation in anesthetized rats

The effects of the pharyngeal non-noxious mechanical stimulation on the secretion of immunoreactive thyroxin (iT4), immunoreactive calcitonin (iCT), and immunoreactive parathyroid hormone (iPTH) into thyroid venous blood were examined in anesthetized rats. Secretion rates of iT4, iCT, and iPTH were calculated from their concentration in thyroid venous plasma and the plasma flow rate. A mechanical stimulation was delivered to the pharynx by a rubber balloon placed on the tongue that was intermittently pushed into the pharyngeal cavity. Pharyngeal stimulation increased iT4 and iCT secretion, but iPTH secretion was unchanged. The secretion responses were abolished by transecting the superior laryngeal nerves (SLNs) bilaterally. The activities of the thyroid parasympathetic efferent nerves and the afferent nerves in the SLN increased significantly during pharyngeal stimulation. These results indicate that pharyngeal mechanical stimulation promotes thyroxin and calcitonin secretion from the thyroid gland by a reflex increase in SLN parasympathetic efferent activity, triggered by excitation of SLN mechanoreceptive afferents.

Vagal Paraganglioma: Surgical Removal with Superior Laryngeal Nerve Preservation

Vagal paragangliomas (VPGLs) represent <5% of all head and neck paragangliomas (PGLs) and show a 17% to 20% risk of malignancy. We present a rare case of a 50-year-old gender with a left VPGL in her neck. To date, approximately 200 cases have been reported. The tumor showed web-like adhesions and arterial supply from the external carotid artery. We performed en bloc resection including a part of the vagus nerve. The superior laryngeal nerve was preserved with the “human communicating nerve” which maintains neural communication in >70% of humans, providing motor fibers to the larynx. The patient recovered uneventfully and was discharged on the 3rd postoperative day. These tumors are therapeutically challenging owing to their proximity to vital neck and skull base structures. Early detection decreases surgical morbidity and mortality. Preservation of viable neural tissue is important in advanced disease.

Effects of pharmacological lesion of the nucleus retroambiguus region on the pharyngeal phase of swallowing

Pharyngeal swallowing is controlled by synaptic interactions within a swallowing central pattern generator (sw-CPG) that is composed of a dorsal and a ventral swallowing group (VSG). Here, we used electrical stimulation (10 s) of the superior laryngeal nerve (SLN; 20 Hz; pulse width: 100 μs) to explore the role of the VSG in an arterially-perfused brainstem preparation of rats. To investigate the effects of pharmacological lesion (local microinjection of an GABA(A)-R agonist) of the nucleus retroambiguus (NRA), a designated component of the VSG, we recorded phrenic (PNA) and vagal nerve (VNA) activities. Control SLN stimulation with stepwise increasing stimulus intensities (from 20 μA to 160 μA) elicited robust suppression of PNA and evoked sequential swallowing activity in the VNA. Lesioning of the NRA had no effect on the pattern of pharyngeal swallowing, but significantly increased the sensory gating of SLN inputs. We conclude that the NRA is not part of the VSG, but appears to have important roles for the central gating of swallowing.

Superior Laryngeal Nerve Neuralgia: Case Series and Review of Anterior Neck Pain Syndromes

Superior laryngeal nerve neuralgia (SLNN) is an anterior neck pain syndrome that is underrecognized and, as a result, is often misdiagnosed. We present a series of patients who were diagnosed with and subsequently treated for SLNN. Nineteen patients were treated with oral nonsteroidal anti-inflammatory drugs (NSAIDs) and/or a therapeutic neck injection with 2% lidocaine and 40% triamcinolone acetonide. All patients completed a visual analog scale (VAS) to rate the level of pain before and after treatment. Four patients rated their pain as mild, 14 as moderate, and 1 as severe according to the VAS. Of the 19 patients, 8 chose to proceed with a 2-week course of NSAIDs and only 1 of them had complete resolution of their symptoms. A total of 18 patients underwent therapeutic neck injections, with a complete response to injection therapy in 10 patients. Five patients described a minimal residual foreign body sensation and 3 patients complained of mild residual pain. In this study, we found that therapeutic neck injections are effective not only in confirming the diagnosis but also in treating pain.

Activation of TRPV1 and TRPM8 Channels in the Larynx and Associated Laryngopharyngeal Regions Facilitates the Swallowing Reflex

The larynx and associated laryngopharyngeal regions are innervated by the superior laryngeal nerve (SLN) and are highly reflexogenic. Transient receptor potential (TRP) channels have recently been detected in SLN innervated regions; however, their involvement in the swallowing reflex has not been fully elucidated. Here, we explore the contribution of two TRP channels, TRPV1 and TRPM8, located in SLN-innervated regions to the swallowing reflex. Immunohistochemistry identified TRPV1 and TRPM8 on cell bodies of SLN afferents located in the nodose-petrosal-jugular ganglionic complex. The majority of TRPV1 and TRPM8 immunoreactivity was located on unmyelinated neurons. Topical application of different concentrations of TRPV1 and TRPM8 agonists modulated SLN activity. Application of the agonists evoked a significantly greater number of swallowing reflexes compared with the number evoked by distilled water. The interval between the reflexes evoked by the agonists was shorter than that produced by distilled water. Prior topical application of respective TRPV1 or TRPM8 antagonists significantly reduced the number of agonist-evoked reflexes. The findings suggest that the activation of TRPV1 and TRPM8 channels present in the swallowing-related regions can facilitate the evoking of swallowing reflex. Targeting the TRP channels could be a potential therapeutic strategy for the management of dysphagia.

Effect of peripherally and cortically evoked swallows on jaw reflex responses in anesthetized rabbits

This study aimed to investigate whether the jaw-opening (JOR) and jaw-closing reflexes (JCR) are modulated during not only peripherally, but also centrally, evoked swallowing. Experiments were carried out on 24 adult male Japanese white rabbits. JORs were evoked by trigeminal stimulation at 1 Hz for 30 s. In the middle 10 s, either the superior laryngeal nerve (SLN) or cortical swallowing area (Cx) was simultaneously stimulated to evoke swallowing. The peak-to-peak JOR amplitude was reduced during the middle and late 10-s periods (i.e., during and after SLN or Cx stimulation), and the reduction was dependent on the current intensity of SLN/Cx stimulation: greater SLN/Cx stimulus current resulted in greater JOR inhibition. The reduction rate was significantly greater during Cx stimulation than during SLN stimulation. The amplitude returned to baseline 2 min after 10-s SLN/Cx stimulation. The effect of co-stimulation of SLN and Cx was significantly greater than that of SLN stimulation alone. There were no significant differences in any parameters of the JCR between conditions. These results clearly showed that JOR responses were significantly suppressed, not only during peripherally evoked swallowing but also during centrally evoked swallowing, and that the inhibitory effect is likely to be larger during centrally compared with peripherally evoked swallowing. The functional implications of these results are discussed.

Differential response properties of peripherally and cortically evoked swallows by electrical stimulation in anesthetized rats

We compared onset latency, motor-response patterns, and the effect of electrical stimulation of the cortical masticatory area between peripherally and cortically evoked swallows by electrical stimulation in anesthetized rats. The number of swallows and the motor patterns were determined using electromyographic recordings from the thyrohyoid, digastric, and masseter muscles. The onset latency of the first swallow evoked by electrical stimulation of the cortical swallowing area (Cx) was significantly longer than that evoked by stimulation of the superior laryngeal nerve (SLN). The duration of thyrohyoid burst activity associated with SLN-evoked swallows was significantly longer than that associated with either Cx-evoked or spontaneous swallows. Combining Cx with SLN stimulation increased the number of swallows at low levels of SLN stimulation. Finally, A-area (the orofacial motor cortex) stimulation inhibited Cx-evoked swallows significantly more than it inhibited SLN-evoked swallows. These findings suggest that peripherally and cortically evoked swallows have different response properties and are affected differently by the mastication network.

The thyrohyoid membrane as a target for ultrasonography-guided block of the internal branch of the superior laryngeal nerve

STUDY OBJECTIVE

The objective was to present a proof of concept for a simple and consistently successful ultrasonograpy (US)-guided technique to block the internal branch of the superior laryngeal nerve (iSLN).

DESIGN

This was a volunteer and cadaver anatomy study.

SETTING

The setting was an anesthesiology department and an anatomy laboratory at a medical school

MEASUREMENTS

H13-6 MHz US scans were performed in 40 healthy volunteers positioned supine and with extended necks. The goals were to identify the thyrohyoid membrane, measure its depth (in centimeters) using the shortest vertical distance from the skin, and record the scanning time (in seconds) needed to obtain the optimal image. Anatomical dissection was performed with an operating microscope bilaterally on 5 adult cadaver heads, fixed in formalin, to expose the point of iSLN penetration through the thyrohyoid membrane. The distance between the greater horn of the hyoid bone and the nerve entry point into the thyrohyoid membrane was measured. Ultrasonography-guided in-plane injections were performed unilaterally with 22-gauge 50-mm nerve block needles in 3 fresh cadavers with 2-mL lidocaine/methylene blue mixture deposited under direct vision just superficial to the thyrohyoid membrane to evaluate technical feasibility and injectate spread.

MAIN RESULTS

Anatomically, the iSLN was identified in all formalin-preserved cadavers, with hyoid bone greater horn to nerve-membrane interface distances measuring 1.0-2.4 cm (mean, 2.0 cm; SD, 0.5). Sonographically, the iSLN was not visualized, whereas the hyoid bone and the thyrohyoid membrane were visualized in all volunteers. The mean distance from skin to thyrohyoid membrane was 1.69 cm (SD, 0.38). The mean time needed to scan was 15 seconds (SD, 2.3). After US-guided injection, the dye deposition was observed around the iSLN in all cadaver specimens.

CONCLUSIONS

A simpler and consistently reproducible US-guided iSLN block is feasible using the thyrohyoid membrane as target plane for local anesthetic injection. Clinical trials are needed to determine its effectiveness and safety, needle entry point, trajectory, and local anesthetic volume.

Suppression of the swallowing reflex by stimulation of the red nucleus

We study whether the red nucleus is involved in control of swallowing. The swallowing reflex was induced in anesthetized rats by repetitive electrical stimulation of the superior laryngeal nerve. The electromyographic activities of the mylohyoid and thyrohyoid muscles were recorded in order to identify the swallowing reflex. Repetitive electrical stimulation applied to the red nucleus reduced the number of swallows. The onset latency of the first swallow was increased during repetitive electrical stimulation applied to the magnocellular part of the red nucleus. Microinjection of monosodium glutamate into the red nucleus also reduced the number of swallows. The onset latency of the first swallow was increased after microinjection of monosodium glutamate into the magnocellular part of the red nucleus. These results imply that the red nucleus is involved in the control of swallowing.

Electrophysiological neuromonitoring of the laryngeal nerves in thyroid and parathyroid surgery: A review

Recurrent laryngeal nerve (RLN) injury is one of the most common complications of thyroid surgery. Injury to the external branch of the superior laryngeal nerve is less obvious and affects the voice variably; however, it can be of great significance to professional voice users. Recent literature has led to an increase in the use of neuromonitoring as an adjunct to visual nerve identification during thyroid surgery. In our review of the literature, we discuss the application, efficacy and safety of neuromonitoring in thyroid surgery. Although intraoperative neuromonitoring (IONM) contributes to the prevention of laryngeal nerves injury, there was no significant difference in the incidence of RLN injury in thyroid surgery when IONM was used compared with visual identification alone. IONM use is recommended in high risk patients; however, there are no clear identification criteria for what constitutes “high risk”. There is no clear evidence that IONM decreases the risk of laryngeal nerve injury in thyroid surgery. However, continuous IONM provides a promising tool that can prevent imminent nerve traction injury by detecting decreased amplitude combined with increased latency.

Changes in the frequency of swallowing during electrical stimulation of superior laryngeal nerve in rats

The aim of the present study was to investigate the adaptation of the swallowing reflex in terms of reduced swallowing reflex initiation following continuous superior laryngeal nerve stimulation. Forty-four male Sprague Dawley rats were anesthetized with urethane. To identify swallowing, electromyographic activity of the left mylohyoid and thyrohyoid muscles was recorded. To evoke the swallowing response, the superior laryngeal nerve (SLN), recurrent laryngeal nerve, or cortical swallowing area was electrically stimulated. Repetitive swallowing evoked by continuous SLN stimulation was gradually reduced, and this reduction was dependent on the resting time duration between stimulations. Prior SLN stimulation also suppressed subsequent swallowing initiation. The reduction in evoked swallows induced by recurrent laryngeal nerve or cortical swallowing area stimulation was less than that following superior laryngeal nerve stimulation. Decerebration had no effect on the reduction in evoked swallows. Prior subthreshold stimulation reduced subsequent initiation of swallowing, suggesting that there was no relationship between swallowing movement evoked by prior stimulation and the subsequent reduction in swallowing initiation. Overall, these data suggest that reduced sensory afferent nerve firing and/or trans-synaptic responses, as well as part of the brainstem central pattern generator, are involved in adaptation of the swallowing reflex following continuous stimulation of swallow-inducing peripheral nerves and cortical areas.

Superior laryngeal nerve block: an anatomical study comparing two techniques

STUDY OBJECTIVE

To determine whether an anterior approach is as successful as the conventional posterior approach to superior laryngeal nerve block.

DESIGN

Prospective observational study.

SETTING

University anatomy laboratory.

PATIENTS

20 formalin-fixed adult human cadavers.

MEASUREMENTS

Simulated superior laryngeal nerve blocks were performed by a single operator using 3 mL of 0.01% analine blue dye with a 23-gauge Quincke tip needle. Two different landmark techniques were used on each undissected cadaver: 1) the conventional posterior approach using the hyoid bone as a palpable landmark, with injection at the posterior third of the thyrohyoid membrane; and 2) the anterior approach, using the anterior thyroid notch of the thyroid cartilage, with injection at the anterior third of the thyrohyoid membrane. The spread of analine dye was observed. An injection was deemed successful if the entire paraglottic space was stained or the superior laryngeal nerve stained as it entered the paraglottic space.

MAIN RESULTS

Both techniques were equally successful after 40 injections.

CONCLUSION

There was no significant difference in success in staining the superior laryngeal nerve in human cadavers between the conventional posterior approach and an anterior approach.

The evolution of laryngeal reinnervation, the current state of science and thoughts for future treatments

The treatment of unilateral vocal fold palsy (UVFP) or bilateral vocal fold palsy (BVFP) has been the subject of debate and experiment for 150 years. To date, dozens of different surgical methods have been described to reinnervate this most complex of organs, the larynx. As yet, there is no consensus on the most functionally effective method of reinnervation. However, it is a rapidly expanding area of research and remains an area of controversy. Indications for reinnervation for both UVFP and BVFP are still evolving and our understanding of the neuromuscular supply to the larynx continues to expand. What may have been considered unacceptable results from previous studies with one pathology may actually be of benefit in patients with different pathologies. This uncertainty of treatment options and potential outcomes can be confusing. In addition alternative techniques have been postulated as mainstays or adjuncts of treatment to the stalwart of reinnervation, neurorrhaphy. Determining what the correct treatment for an individual patient should be is still a gray area. With this in mind, this article reviews the evolution of laryngeal reinnervation, reviews the current state of the science, and suggests directions in which it might move in the future.

Facilitation of the swallowing reflex with bilateral afferent input from the superior laryngeal nerve

To determine the cooperative effect of laryngeal afferent signals on the swallowing reflex, we examined whether afferent signals originating from the left and right superior laryngeal nerve (SLN) modulates elicitation of the swallowing reflex in urethane-anesthetized rats. Mylohyoid electromyographic activity was recorded to quantify the swallowing reflex. The onset latency of the swallowing reflex and the time intervals between successive swallows were used to quantify and compare the effects of unilateral and bilateral electrical stimulations of the SLN. The mean latency of the first swallow and the mean time interval between swallows evoked with low frequency stimulation were both significantly different between unilateral and bilateral stimulations of the SLN. These findings suggest that facilitatory effect of afferent signals originating from the SLN bilaterally increase the motoneuronal activity in the medullary swallowing center and enhance the swallowing reflex.

Neuromuscular electrical stimulation of the cricothyroid muscle in patients with suspected superior laryngeal nerve weakness

In this retrospective case study, we report the apparent clinical effectiveness of neuromuscular electrical stimulation (NMES) in combination with voice therapy (VT) for rehabilitating dysphonia secondary to suspected superior laryngeal nerve (SLN) weakness in two female patients. Both patients failed or plateaued with traditional VT but had significant improvement with the addition of NMES of the cricothyroid muscle and SLN using a VitalStim unit. Stimulation was provided simultaneously with voice exercises based on musical phonatory tasks. Both acoustic analysis and endoscopic evaluation demonstrated important improvements after treatment. In the first patient, the major change was obtained within the primo passaggio region; specifically, a decrease in voice breaks was demonstrated. In the second patient, an improvement in voice quality (less breathiness) and vocal range were the most important findings. Additionally, each patient reported a significant improvement in their voice complaints. Neuromuscular laryngeal electrical stimulation in combination with vocal exercises might be a useful tool to improve voice quality in patients with SLN injury.

Effects of asymmetric superior laryngeal nerve stimulation on glottic posture, acoustics, vibration

OBJECTIVES/HYPOTHESIS

Evaluate the effects of asymmetric superior laryngeal nerve stimulation on the vibratory phase, laryngeal posture, and acoustics.

STUDY DESIGN

Basic science study using an in vivo canine model.

METHODS

The superior laryngeal nerves were symmetrically and asymmetrically stimulated over eight activation levels to mimic laryngeal asymmetries representing various levels of superior laryngeal nerve paresis and paralysis conditions. Glottal posture change, vocal fold speed, and vibration of these 64 distinct laryngeal-activation conditions were evaluated by high speed video and concurrent acoustic and aerodynamic recordings. Assessments were made at phonation onset.

RESULTS

Vibratory phase was symmetric in all symmetric activation conditions, but consistent phase asymmetry toward the vocal fold with higher superior laryngeal-nerve activation was observed. Superior laryngeal nerve paresis and paralysis conditions had reduced vocal fold strain and fundamental frequency. Superior laryngeal nerve activation increased vocal fold closure speed, but this effect was more pronounced for the ipsilateral vocal fold. Increasing asymmetry led to aperiodic and chaotic vibration.

CONCLUSIONS

This study directly links vocal-fold tension asymmetry with vibratory phase asymmetry, in particular the side with greater tension leads in the opening phase. The clinical observations of vocal fold lag, reduced vocal range, and aperiodic voice in superior laryngeal paresis and paralysis is also supported.

The effect of unilateral superior laryngeal nerve lesion on swallowing threshold volume

OBJECTIVES/HYPOTHESIS

The superior laryngeal nerve (SLN) is the major sensory nerve for the upper larynx. Damage to this nerve impacts successful swallowing. The first aim of the study was to assess the effect of unilateral SLN lesion on the threshold volume sufficient to elicit swallowing in an intact pig model; this volume was defined radiographically as the maximum bolus area visible in lateral view. The second aim was to determine if a difference existed between ipsilateral and contralateral function as a result of unilateral sensory loss, measured as the radiologic density of fluid seen in the valleculae. Finally, we determined whether there was a relationship between the threshold volume and the occurrence of aspiration after a unilateral SLN lesion.

STUDY DESIGN

Repeated measures animal study.

METHODS

Four female infant pigs underwent unilateral SLN lesion surgery. The maximum vallecular bolus area in lateral view and the relative vallecular density on each side in the dorsoventral view were obtained from videofluoroscopic recordings in both the prelesion control and postlesion experimental states.

RESULTS

In lateral view, the lesioned group had a larger maximum bolus area than the control group (P < .001). Although occasional left-right asymmetry in the dorsoventral view was observed, the vallecular densities were, on average, equal on both the left (intact) and right (lesioned) sides (P > .05). A bigger maximum bolus area did not predict aspiration in the lesioned group (P > .05).

CONCLUSIONS

Unilateral SLN lesions increased the swallowing threshold volume symmetrically in right and left valleculae, but the increased threshold may not be the main mechanism for the occurrence of aspiration.

The superior laryngeal nerve injury of a famous soprano, Amelita Galli-Curci

The superior laryngeal nerve (SLN) has been attributed much less clinical significance than the recurrent laryngeal nerve. It has sometimes been described as the 'neglected' nerve in thyroid surgery, although injury to this nerve can cause significant disability. The external branch of the SLN is the only motor supply to the cricothyroid muscle, which increases the tension of the ipsilateral vocal fold during highfrequency phonation, particularly in women and voice professionals. Damage to this nerve can manifest as ipsilateral cricothyroid muscle paralysis, and clinical symptoms may include a hoarse, breathy voice, frequent throat clearing, vocal fatigue or diminished vocal frequency range, especially when rising pitch. SLN paralysis can be a significant issue for those whose careers depend largely on a full range of voice. The famous opera soprano, Amelita Galli-Curci, suffered SLN injury during thyroid surgery with distressing consequences.

Bilateral internal superior laryngeal nerve palsy of traumatic cervical injury patient who presented as loss of cough reflex after anterior cervical discectomy with fusion

Injury to the bilateral internal branch of superior laryngeal nerve (ibSLN) brings on an impairment of the laryngeal cough reflex that could potentially result in aspiration pneumonia and other respiratory illnesses. We describe a patient with traumatic cervical injury who underwent bilateral ibSLN palsy after anterior cervical discectomy with fusion (ACDF). An 75-year-old man visited with cervical spine fracture and he underwent ACDF through a right side approach. During the post-operative days, he complained of high pitched tone defect, and occasional coughing during meals. With a suspicion of SLN injury and for the work up for the cause of aspiration, we performed several studies. According to the study results, he was diagnosed as right SLN and left ibSLN palsy. We managed him for protecting from silent aspiration. Swallowing study was repeated and no evidence of aspiration was found. The patient was discharged with incomplete recovery of a high pitched tone and improved state of neurologic status. The SLN is an important structure; therefore, spine surgeons need to be concerned and be cautious about SLN injury during high cervical neck dissection, especially around the level of C3-C4 and a suspicious condition of a contralateral nerve injury.

Voice examination in patients with decreased high pitch after thyroidectomy

Decreased high pitch after thyroidectomy due to injury of the external branch of superior laryngeal nerve (EBSLN) may be a critical, especially to professional voice users. The author studied the usefulness of VRP (voice range profile) and MDVP (multi-dimensional voice program) to evaluate patients who have decreased high pitch after thyroidectomy. A study was performed with 58 females and 9 males who underwent voice assessment between January 2008 and June 2009. The patients were classified as the group of female with no decreased high pitch (group A, n = 52), decreased high pitch (group B, n = 6) and the group of male with no decreased high pitch (group C, n = 9). VRP and laryngeal electromyogram (EMG) was performed in group B.

RESULTS

The preoperative frequency range of group A and B were statistically not different. In Group B, the result of VRP showed that the frequency range was 443.11 ± 83.97, 246.67 ± 49.41, 181.37 ± 80.13 Hz showing significant decrease after the surgery compared to that of the preoperative result. (P < 0.05) In addition, the intensity range was 22.25 ± 2.87, 15.25 ± 2.22, 16.25 ± 2.63 dB respectively showing significant postoperative decrease. (P < 0.05) EMG of the cricothyroid muscle of group B showed decreased potential with 3 patients, normal potential in 2, and the other patient refused to take the examination. In group A and C, the result of VRP revealed no significant difference between the preoperative and postoperative result. VRP is a noninvasive, quick, and practical test to demonstrate decreased frequency range visually and helps to evaluate EBSLN injury in patient with thyroidectomy.

Post-thyroidectomy dysphonia in patients with bilateral resection of the superior laryngeal nerve: a comparative spectrographic study

The most serious complications of total thyroidectomy, in cases of widespread and invasive diseases, are mainly hypoparathyroidism and laryngeal inferior nerve palsy. Lesions of the external branch of superior laryngeal nerve instead, although less obvious than the those caused by the recurrent laryngeal nerve lesions, have been taken less into consideration. The frequency of this lesion varies from 14% to 20% of cases, although in reality it is underestimated; in fact, on the one hand it is difficult to assess this, and on the other, post-thyroidectomy dysphonia is often considered inevitable. In the present retrospective research, 15 thyroidectomized patients (4 male, 11 female), have been subjected to qualitative and quantitative evaluation of the voice. Of these, 7 had a nerve lesion, while 8 did not. All the patients received a self-evaluation voice questionnaire (VHI). In all cases, a videolaryngostroboscopy has been carried out and the voice acoustic features examined through a spectrographic analysis. The results showed that removal of the thyroid, at the end of a 12-month post-surgery period, still causes an impact on the qualitative and quantitative aspects of the vocal function, whether the superior larynx nerve was injured or not. The majority of the patients, in both groups, reported that their voice had worsened in quality and durability. Hence, we have shown that the patients with upper larynx nerve lesion have an alteration of F0, show a lower energy level and a modified spectrographic quality compared to patients without injury. This low voice is often considered by patients as a normal consequence of thyroid surgery. The present research confirms that the attempt to identify and protect the superior laryngeal nerve is essential to prevent post-thyroidectomy dysphonia, but this is not sufficient to obtain the best results because of the existence of muscular and psychogenic factors that reduce the still voice capacity of the patient.