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      The Location of the Parasympathetic Fibres within the Vagus Nerve Rootlets: A Case Report and a Review of the Literature

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          Abstract

          The vagus nerve has motor, sensory, and parasympathetic components. Understanding the nerve's internal anatomy, its variations, and relationship to the glossopharyngeal nerve are crucial for neurosurgeons decompressing the lower cranial nerves. We present a case report demonstrating the location of the parasympathetic fibres within the vagus nerve rootlets. A 47-year-old woman presented with a 1-year history of medically refractory left-sided glossopharyngeal neuralgia and a more recent history of left-sided hemi-laryngopharyngeal spasm. magnetic resonance imaging showed her left posterior inferior cerebellar artery distorting the lower cranial nerves on the affected left side. The patient consented to microvascular decompression of the lower cranial nerves with possible sectioning of the glossopharyngeal and upper sensory rootlets of the vagus nerve. During surgery, electrical stimulation of the most caudal rootlet of the vagus nerve triggered profound bradycardia. None of the more rostral rootlets had a similar parasympathetic response. This case is the first demonstration, to our knowledge, of the location of the cardiac parasympathetic fibres within the human vagus nerve rootlets. This new understanding of the vagus nerve rootlets' distribution of pure sensory (most rostral), motor/sensory (more caudal), and parasympathetic (most caudal) fibres may lead to a better understanding and diagnosis of the vagal rhizopathies. Approximately 20% of patients with glossopharyngeal neuralgia also have paroxysmal cough. This could be due to the anatomical juxtaposition of the IXth cranial nerve with the rostral vagal rootlets with pure sensory fibres (which mediate a tickling sensation in the lungs). A subgroup of patients with glossopharyngeal neuralgia have neuralgia-induced syncope. The cause of this rare condition, “vago-glossopharyngeal neuralgia,” has been debated since it was first described by Riley in 1942. Our case supports the theory that this neuralgia-induced bradycardia is reflexively mediated through the brainstem with afferent impulses in the IXth and efferent impulses in the Xth cranial nerve. The rarer co-occurrence of glossopharyngeal neuralgia with hemi-laryngopharyngeal spasm (as seen in this case) may be explained by the proximity of the IXth nerve with the more caudal vagus rootlets which have motor (and probably sensory) supply to the throat. Finally, if there is a vagal rhizopathy related to compression of its parasympathetic fibres, one would expect it to be at the most caudal rootlet of the vagus nerve.

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          Most cited references15

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          Vagus Nerve and Vagus Nerve Stimulation, a Comprehensive Review: Part I.

          The vagus nerve (VN), the "great wondering protector" of the body, comprises an intricate neuro-endocrine-immune network that maintains homeostasis. With reciprocal neural connections to multiple brain regions, the VN serves as a control center that integrates interoceptive information and responds with appropriate adaptive modulatory feedbacks. While most VN fibers are unmyelinated C-fibers from the visceral organs, myelinated A- and B-fiber play an important role in somatic sensory, motor, and parasympathetic innervation. VN fibers are primarily cholinergic but other noncholinergic nonadrenergic neurotransmitters are also involved. VN has four vagal nuclei that provide critical controls to the cardiovascular, respiratory, and alimentary systems. Latest studies revealed that VN is also involved in inflammation, mood, and pain regulation, all of which can be potentially modulated by vagus nerve stimulation (VNS). With a broad vagal neural network, VNS may exert a neuromodulatory effect to activate certain innate "protective" pathways for restoring health.
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            Myths and realities of the cardiac vagus.

            J Coote (2013)
            There is continuing belief that cardiac parasympathetic postganglionic fibres are sparse or absent from the ventricles. This review of the literature shows that the supposition is a myth. Early studies considered that fine silver-stained fibres coursing amongst ventricle myocardial cells were most likely cardiac parasympathetic postganglionic fibres. The conclusions were later supported by acetyl cholinesterase staining using a method that appeared not to be associated with noradrenaline nerve fibres. The conclusion is critically examined in the light of several recent histological studies using the acetyl cholinesterase method and also a more definitive technique (CHAT), that suggest a widespread location of parasympathetic ganglia and a relatively dense parasympathetic innervation of ventricular muscle in a range of mammals including man. The many studies demonstrating acetylcholine release in the ventricle on vagal nerve stimulation and a high density of acetylcholine M2 receptors is in accord with this as are tests of ventricular performance from many physiological studies. Selective control of cardiac functions by anatomically segregated parasympathetic ganglia is discussed. It is argued that the influence of vagal stimulation on ventricular myocardial action potential refractory period, duration, force and rhythm is evidence that vagal fibres have close apposition to myocardial fibres. This is supported by clear evidence of accentuated antagonism between sympathetic activity and vagal activity in the ventricle and also by direct effects of vagal activity independent of sympathetic activity. The idea of differential control of atrial and ventricular physiology by vagal C and vagal B preganglionic fibres is examined as well as differences in chemical phenotypes and their function. The latter is reflected in medullary and supramedullary control. Reference is made to the importance of this knowledge to understanding the normal physiology of cardiac autonomic control and significance to pathology.
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              Neuralgia of the glossopharyngeal and vagal nerves: long-term outcome following surgical treatment and literature review.

              This study describes our experience in the surgical treatment of neuralgia of the glossopharyngeal and vagal nerves. Over the last 19 years, 21 patients underwent surgery. Their case notes were reviewed to obtain demographic information, clinical presentation, surgical findings and early results. All patients were then contacted by telephone for long-term results and complications. Independent analysis of results was carried out by a Neurology team. Ten patients had microvascular decompression (MVD). Four patients had MVD and nerve section. In the remaining seven patients, the glossopharyngeal and first two rootlets of the vagal nerve were sectioned. Nineteen (90%) of 21 patients experienced complete relief of pain immediately after surgery. The remaining patients reported an improvement in their symptoms. There were no mortalities. Four patients experienced short-term complications, which resolved. Two patients were left with a persistent hoarse voice. At follow-up (mean duration of 4 years), there was no recurrence in symptoms. In our experience, surgery is safe and effective for the treatment of vago-glossopharyngeal neuralgia.
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                Author and article information

                Journal
                Stereotact Funct Neurosurg
                Stereotact Funct Neurosurg
                SFN
                Stereotactic and Functional Neurosurgery
                S. Karger AG (Allschwilerstrasse 10, P.O. Box · Postfach · Case postale, CH–4009, Basel, Switzerland · Schweiz · Suisse, Phone: +41 61 306 11 11, Fax: +41 61 306 12 34, karger@karger.com )
                1011-6125
                1423-0372
                February 2023
                29 December 2022
                29 December 2022
                : 101
                : 1
                : 68-71
                Affiliations
                [1] aDivision of Neurosurgery, University of British Columbia, Vancouver, British Columbia, Canada
                [2] bDivision of Neurosurgery, Hamad General Hospital, Doha, Qatar
                Author notes
                Article
                sfn-0101-0068
                10.1159/000528094
                9986834
                36580909
                6d044abb-3acf-4b88-aa3e-d12a8e6c9caf
                Copyright © 2022 by The Author(s). Published by S. Karger AG, Basel

                This article is licensed under the Creative Commons Attribution-NonCommercial 4.0 International License (CC BY-NC). Usage and distribution for commercial purposes requires written permission.

                History
                : 30 August 2022
                : 3 November 2022
                : 2023
                Page count
                Figures: 2, References: 15, Pages: 4
                Funding
                No funding was obtained for the publication of the article. Open Access funding was provided by the Qatar National library.
                Categories
                Case Series

                glossopharyngeal nerve,glossopharyngeal neuralgia,vago-glossopharyngeal neuralgia,parasympathetic vagus nerve,microvascular decompression

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