Overview of Vagus nerve anatomy:
Cranial nerve ten (CN X), the vagus nerve, is a functionally diverse yet critical mediator of assorted modalities of innervation. The vagus nerve has the longest course of all cranial nerves and extends from the head to the abdomen (Fig 1). It elicits sensory, special sensory, motor and parasympathetic innervation along its route and therefore is composed of both sensory and motor fibres. Primarily, the vagus nerve will supply organs of the thorax and abdomen (Baccaro et al., 2013).
Figure 1. Course of vagus nerve (CN X) from the head to the abdomen with all corresponding branches evidenced. (Taken from Kim [Kenhub], 2018)
Originating from the medulla of the brainstem, the vagus nerve travels via the jugular foramen with the glossopharyngeal and accessory nerve. The auricular branches arise within the cranium to supply sensation to the posterior external auditory canal and external ear. Within the neck, the vagus nerve will pass through the carotid sheath, travelling inferiorly to the jugular vein and common carotid artery (Rohen et al., 1998). At the base of the neck, the right and left vagus nerves will follow different pathways. Within the neck various branches of the vagus nerve arise including the pharyngeal branches, superior laryngeal nerve and the recurrent laryngeal nerve (on the right side only). The right vagus nerve will pass anteriorly to the subclavian artery and posteriorly to the sternoclavicular joint to enter the thorax. It then travels posteriorly to both the aortic arch and right primary bronchus. The left vagus nerve will pass inferiorly between the left common carotid and left subclavian artery and posterior to the sternoclavicular joint to enter the thorax (Rohen et al., 1998; Baccaro et al., 2013). It then travels anteriorly to the aortic arch and posteriorly to the left primary bronchus before reaching the oesophagus. The vagi will then reform in the lower thorax as anterior and posterior trunks. At approximately the level of the 10
thoracic vertebra, the vagus will pierce through the diaphragm, travelling with the oesophagus. At this point, the vagus will supply the abdomen via three branches (Baccaro et al., 2013).
- Gastric Branch
The right vagus nerve branches will form the posterior gastric plexus on the postero-inferior surface of the stomach. The left vagus nerve will form the anterior gastric plexus on the antero-superior surface of the stomach (Fig 2). Both these divisions and plexi are located between the layers of the lesser omentum. Anterior gastric fibres will extend to the upper duodenum and pylorus, while the posterior vagal trunk and posterior gastric branches will supply fibres to the abdominal autonomic plexus. From here, vagal fibres will be dispersed to regions surrounding coeliac, renal and superior mesenteric arteries (Rohen et al., 1998; Baccaro et al., 2013).
Figure 2. The branching of the vagus nerve in the abdomen. Anterior gastric branches of the anterior vagal trunk are observed to supply the antero-superior surface of the stomach (Taken from Kim, 2018)
- Coeliac branches
The right vagus nerve derives the coeliac branch of the vagus nerve. These will join the coeliac plexus innervating the pancreas, kidneys, spleen, suprarenals and intestine (Fig 3) (Rohen et al., 1998; Baccaro et al., 2013).
- Hepatic branches
The left vagus nerve will give rise to the hepatic branch and will join with the hepatic plexus to travel along the lesser omentum towards the liver (Fig 3) (Rohen et al., 1998; Baccaro et al., 2013).
Figure 3. Depicted course of coeliac branch and hepatic branch of anterior vagal trunk (Taken from Kim, 2018)
Introduction to Vagotomy
Gastric peptic ulcers are a form of gastrointestinal disease, evolving from disorders such as gastrointestinal reflux and heartburn. Complicated cases of gastric peptic ulcers can be managed through vagotomy. Vagotomy is a surgical procedure involving disconnection of the branches of the vagus nerve to reduce or disable the production and secretion of stomach acid (Seeras & Prakash, 2019). Generally, this is a final resort when medications, diet alterations and alternative management strategies elicit no effect on patients suffering from peptic ulcer disease (PUD). Vagotomy will be performed on patients suffering from severe complications of peptic ulcers including perforation, bleeding, recurrent ulcer formation and obstruction of digestive flow (Clement et al., 2017; Seeras & Prakash, 2019). The principle underlying vagotomy is owed to the anatomical and functional understanding of the vagus nerve. Since, the vagus nerve plays a central role in acid section, the disruption of vagal innervation is founded to be an antisecretory measure. Therefore, the primary aim of vagotomy is to reduce gastric acid secretion in patients developing complications from PUD (Lipof et al., 2006). Surgical vagotomy has historically played a crucial role in the treatment of PUD and was considered as the frontline gold standard method for PUD treatment in the late 1940s. The introduction of acid-reducing medications led to a drastic decrease in the vagotomy procedures performed in the late 1970s. The number of vagotomies performed in emergency cases however still persists (Seeras & Prakash, 2019; Lipof et al., 2006).
There are 4 main types of surgical vagotomies that may be performed.
Highly selective vagotomy.
This involves disconnecting nerve branches supplying the acid-secreting glands of the stomach. Divisions supplying antrum, hepatic and coeliac branches are preserved.
Parietal cell vagotomy.
This utilises a selective severing of nerve fibres which supply the proximal two-thirds of the stomach. This is predominantly performed on patients with duodenal ulcers.
This encompasses disconnection of the vagal nerves entering the stomach with the hepatic and coeliac branches preserved from disconnection. This procedure is rarely performed.
Truncal or total abdominal vagotomy.
This involves disconnection of the two main vagus nerve trunks entering the abdomen. Drainage procedures such as pyloroplasty are conjunctively performed along with truncal vagotomy (Seeras & Prakash, 2019).
Advances in medication and the understanding of gut microbiota and bacteria have rendered vagotomy procedures as less common modern-day approaches to treating PUD. Moreover, only 5% of bleeding ulcers eventuate in operative measures (Lipof et al., 2006). Surgical procedures are only adopted following a failure to achieve haemostasis endoscopically, recurrent bleeding despite attempts at achieving haemostasis and severe perforations (Clement et al., 2017).
Prior to surgery, either a laparotomy or a laparoscopy is performed. A laparotomy is an open surgery, whereby an abdominal incision is created bypassing the abdominal muscle to gain entry into the abdominal cavity. Here, the vagus nerve is identified and located, and the branches of interest are clamped and cut out. A laparoscopy encompasses 4-5 incisions which are created in the abdomen (Lipof et al., 2006; Seeras & Prakash, 2019). A port is passed through one incision and carbon dioxide is then administered through the abdominal cavity for inflation. A laparoscope will then be passed into the abdomen along with other surgical equipment and instruments through the remaining incisions (Baccaro et al., 2013). The vagus nerve is then identified with the laparoscope and instruments. The vagus nerve and the corresponding branches are again clamped and cut out (Seeras & Prakah, 2019).
Vagotomy is generally performed with stomach drainage, pyloroplasty, resection, or diversion procedures to treat PUD complications. Most commonly, pyloroplasty is performed. Vagotomy results in decreased peristalsis and alteration to the emptying patterns of the stomach. Therefore, pyloroplasty encompasses widening the stomach outlet (the pylorus) to the intestine, to accommodate for altered emptying patterns that will proceed post-operatively (Seeras & Prakash, 2019). This conjunctive procedure alleviates the chance of obstruction or delayed emptying (gastroparesis) in the gastrointestinal tract.
Generally, there are potential risks attributed to vagotomy surgical procedures. The following are primary complications that can be exhibited as a result of the procedure (Seeras & Prakah, 2019).
- Internal bleeding following incorrect incision of identification of the vagus nerve. This may result in ruptured arteries or leaking veins
- Post-operative infections
- Shock from blood loss
- Deep vein thrombosis
- Trouble urinating
- Allergic reactions to anaesthesia
- Dumping syndrome which is generally presented with the onset of stomach cramps, nausea and vomiting, diarrheas and tachycardia after eating. This is attributed to the changes in anatomy and physiology following vagotomy surgery.
- Muscle fibre injury (when mistaken for vagal branch)
While vagotomy has lost significance as a primary, frontline technique in treating PUD, its significance arises in alternate areas of medicine. More recently, studies assessing the significance of vagotomy in treating diseases such as Parkinson’s, dementia, ischemic heart disease and obesity has arisen to determine vagotomy as clinically significant in modern day clinical medicine. It also opts for a greater understanding of the multifaceted role of the vagus nerve in treating diseases causing increased levels of morbidity globally. These are particularly attributed in determining a protective ability of deficient vagal signals in attempting to overcome cardiovascular disease, obesity and neurodegenerative illnesses.
Preliminary evidence highlights that truncal vagotomy displays a potential protective effect against Parkinson’s disease. Interestingly, evidence is consistent in suggesting that truncal, but not selective vagotomy is related to a lower risk and incidence of Parkinson’s disease (Liu et al., 2017; Lin et al., 2018) (Fig 4).
Figure 4. Cumulative incidence of Parkinson’s disease following truncal and selective vagotomy. Truncal vagotomy suggests a related lower incidence of Parkinson’s disease (Taken from Liu et al., 2017)
Moreover, subdiaphragmatic vagotomy is also also implicated to prevent weight gain and induce weight loss in severely obese mice (Mc4r -/-). This suggests that weight loss in obesity is a direct result of a loss of signalling in vagal motor neurons (Dezfuli et al., 2018). Hence, publications have deduced that hyperactive vagal efferent signalling underlies hypothalamic obesity syndromes which are ameliorated by sub-diaphragmatic vagotomy (Dezfuli et al., 2018). This poses as a considerable area for further investigation, specifically in human trials to assist with weight management and obesity rates which can be implicated in secondary diseases such as heart disease.
Additionally, acid-reducing vagotomy is also suggested to be associated with a reduced risk of ischemic heart disease. Particularly, patients with PUD are implicated to have increased risks of ischemic heart disease (Koniaris et al., 2016). Thus, vagotomy is attributed to play a central role in decreasing the onset of ischemic heart disease (Koniaris et al., 2016). While, the mechanism of the relationship is unknown, what is clear is that the vagus nerve is implicated in an increased incidence of heart failure. Hence, more findings are needed to support physiological mechanisms in being able to apply specific vagotomy procedures to patient groups with increased genetic and environmental risks of developing ischemic heart disease (Koniaris et al., 2016).
Although now uncommon, surgical vagotomy may still have clinical significance for the treatment of various complications other than PUD. However, in light of this it is still important for physicians to have knowledge of the procedure and its complications to form effective treatment strategies for patients presenting with complicated PUD. Truncal vagotomy has become a generally obsolete procedure following the introduction of proton pump inhibitors (PPIs) such as omeprazole. Nevertheless, emergency vagotomy may be performed in cases where PPIs and other alterations do not elicit any improvements in the disease.
Conclusively, vagotomy procedures require further examination in the treatment of other clinically significant diseases. Several studies in recent years attribute vagotomy to induced neural protection, cardiac protection and weight loss. The scope of these studies are significant in grounding the need for further directional studies incorporating vagotomy as a possible treatment therapy in Parkinson’s disease, dementia, ischemic heart disease and obesity. Therefore, vagotomy resides as a clinically significant procedure in inducing multifaceted therapies encompassing a broad spectrum of affected patients.
Along with understanding the central role of the vagus nerve and its innervating capacity, vagotomy can be manipulated to achieve standardised mechanisms in the treatment of Parkinson’s, dementia, ischemic heart disease and obesity. Hence, the revival and incorporation of this procedure into modern clinical settings is likely to form therapeutic treatments against common health issues. With an increasing obese population, cardiovascular disease resides at the heart of morbidity rates in the general populous. In addition, an aging population also suggests the need for treatment strategies in maintaining neural cognition to overcome neurodegenerative diseases such as Parkinson’s and dementia. Hence, it is critical for vagotomy studies to be emphasised clinically in developing a century old surgical procedure as a modern tool for overcoming modern day health issues.
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