The Pyloric Sphincteric Cylinder in Health and Disease

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Chapter 8 (page 30)

On the right there are the following three main groups of branches:
  1. The first or hepatic branch proceeds laterally in the lesser omentum towards the porta hepatis; it is frequently duplicated. Its terminal twigs are divided into 2 series, viz. a proximal which supplies the porta hepatis, and a distal, which turns downwards towards the pylorus. From the latter twigs pass (a) to the pylorus and first part of the duodenum; (b) along the right gastric artery to the region of the pyloric canal; (c) to run deep to the pylorus with the gastroduodenal artery towards the head of the pancreas and second part of the duodenum; (d) to run proximally on the wall of the hepatic artery, and (e) to communicate with sympathetic twigs passing to the gall bladder. Communications with sympathetic twigs are common.

  2. The second branch on the right, a large nerve, passes downwards between the layers of the lesser omentum, a short distance from, and parallel to, the lesser curvature of the stomach. It is distributed to the anterior surface of the pyloric "antrum" and body of the stomach, but does not reach the pyloric "canal".

  3. The third branch lies on and follows the lesser curvature along the attachment of the lesser omentum; it descends as far as the incisura angularis. All these branches may communicate with the coeliac sympathetic plexus, and in the region of the fornix communications are received from the posterior vagal trunk.

McCrea (l924) concludes that the pyloric canal, pyloric "sphincter" and first part of the duodenum are supplied by the hepatic branches of the anterior vagus. The remainder of the stomach is supplied by the gastric, and second and third right branches. It is stated specifically that the second branch supplies the anterior surface of the "antrum" and body, but that it does not reach the pyloric "canal". McCrea found the distribution of the vagi in the abdomen of the cat, dog and rabbit to be essentially similar to that of man.

Mitchell's (l940) findings differ in certain minor respects from those of McCrea (l924). According to Mitchell some of the lowermost gastric branches (which primarily supply the cardia, fornix and upper lesser curvature) reach almost, but not quite, to the pylorus.

The hepatic branches (of which there are two to four), running towards the right to the porta hepatis, divide at the hepatic artery, one branch passing upwards to the liver and the other downwards to the pylorus and coeliac plexus. In one out of 15 specimens the uppermost hepatic branch divided into three: one to the porta hepatis, one to the cystic duct and gall bladder, and the third to the pylorus.

The greater anterior gastric nerve (i.e. McCrea's second branch) supplies two pyloric twigs according to Mitchell (l940). The first arises near the upper end of the lesser curvature, passes almost horizontally between the layers of the lesser omentum as far as the hepatic artery, then turns downwards on the left side of the hepatic artery to reach the pylorus and proximal part of the duodenum. It often bifurcates, sending one branch upwards to the liver and the other downwards to the pylorus, and it is connected to the hepatic plexus. The other pyloric twig usually arises from the greater anterior gastric nerve about halfway along the lesser curvature, and passes obliquely between the layers of the lesser omentum to the pyloric "antrum", some fibres reaching the pyloric "sphincter". This twig arises at a lower level, but supplies the pylorus proximal to the branch first described.

Thus according to McCrea (l924) and Mitchell (1940), the main innervation of the pyloric region from the anterior vagus occurs via its hepatic branches. According to Mitchell (l940) the pylorus is also innervated by twigs arising in the greater anterior gastric vagal branch, running between the layers of the lesser omentum.

Jackson (l948) studied the distribution of the vagus in 50 cadavers. The hepatic branches of the anterior trunk, running to the porta hepatis, were identified in 43 cases. In the first case the hepatic branch was followed to its termination and was found to supply the first few centimeters proximal to the pylorus, the pylorus itself and the first part of the duodenum. In the remainder of the dissections attention was concentrated on the more proximal parts of the branches, and the hepatic branches were followed only to the fissure of the ductus venosus. The principal anterior nerve of the lesser curvature described by Latarjet (l921) was found in 28 instances. From its origin it passed along the lesser curvature, returning to the stomach generally from 2.5-9 cm proximal to the pylorus; the closest any branch of this nerve came to the pyloric "sphincter" was 2.5 cm.

Skandalakis et al. (l986) reiterate that separation of the anterior vagal trunk into anterior gastric and hepatic divisions is usually found on the surface of the distal oesophagus at the gastro-oesophageal junction. Usually a major branch of the anterior gastric division forms the principal anterior nerve of the lesser curvature (nerve of Latarjet). In most instances it can be traced to the level of the incisura; occasionally it may proceed as far as the first part of the duodenum (in these cases the pylorus is still innervated via the hepatic branch). It may also be absent, the "antrum" being supplied by branches arising from the anterior vagal trunk proximal to the origin of the hepatic division. Many variations exist, and Skandalakis et al. (l986) referred to "the vagaries of the vagus nerve". However, these authors point out that the usual supply to the pylorus is a descending branch (or branches) from the hepatic division before it reaches the liver; occasionally the pyloric branch may arise from the anterior gastric division.

Posterior Vagus

The posterior vagal trunk, which is derived mainly from the right vagus nerve but includes fibres from the left vagus and some sympathetic fibres, enters the abdomen through the oesophageal hiatus in the diaphragm on the posterior surface of the oesophagus. The number and direction of its branches is more constant than that of the anterior vagus (Latarjet l921; Skandalakis et al. l986). Shortly after entering the abdomen it divides into 2 main divisions. The larger or coeliac division proceeds to the coeliac and other abdominal sympathetic plexuses. The smaller or posterior gastric division first gives off fine twigs to the lower oesophagus and fornix.

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