The Pylorus at Gastroscopy #

Schindler (l936) described the interior of the stomach as seen at gastroscopy in patients lying on their left side. In this position the pyloric part falls to the left and forward towards the anterior abdominal wall. While radiologists perceive the incisura angularis as an indentation of the lesser curvature side of the barium column, gastroscopists see it as a prominence or "kind of fold" in the inside of the stomach, called the angulus or angle. According to Schindler the stomach could be divided into two parts: the part above the angulus or pars digestoria, and the part between the angulus and pylorus or pars egestoria. If little air is used for inflation at gastroscopy, another prominent fold, the musculus sphincter antri, becomes visible on the anterior and posterior walls and greater curvature at the level of the angulus. It is a separate entity from the angulus, is probably formed by contraction of the muscularis externa and is usually not demonstrable radiologically.

According to Schindler (l936) peristaltic waves always commence distally to the musculus sphincter antri. Gastroscopically these waves are seen as circular elevations moving towards the pylorus and accompanied by a shortening of the "antrum" until closure of the pylorus is complete. This is often accompanied by the formation of radial mucosal folds, giving the closed pylorus a stellate appearance.

Torgersen (l942) showed that the musculus sphincter antri consisted of a loop at the termination of the oblique fibres of the muscularis externa of the corpus. It was also called the lower segmental loop and formed the oral boundary of the sinus (Chap. 3). Consequently it did not take part in the contractions of the pyloric sphincteric cylinder.

Gastroscopically the pylorus is seen to be open most of the time, according to Johnson (l961). As a wave of peristalsis passes down the "antrum" and reaches the pylorus, the latter is seen to close. It remains closed for only a few seconds, then relaxes, remaining open until it is reached by the next peristaltic wave.

Rider et al. (l967) described the dynamic anatomy of the "antrum" and pylorus. Numerous combined fluroscopic and gastroscopic studies showed that peristaltic waves proceeded through the corpus and proximal part of the "antrum" towards the pylorus. Each wave caused a "pinch-off" in the antrum, creating the appearance of a rosette-like sphincter, called the proximal sphincter. The area beyond this sphincteric action was still part of the stomach and represented the "distal antrum" or "pyloric channel". With relaxation of the proximal sphincter a small, circular distal opening became evident beyond it, which was the pyloric aperture surrounded by the true pyloric ring. It was pointed out that the proximal sphincter could easily be mistaken for the pyloric ring, and in such cases it could erroneously be concluded that a gastroscope which had passed this area was in the duodenal bulb.

Comment: From the above description it is clear that contraction of the "proximal sphincter" is the same occurrence as contraction of the left pyloric loop as seen radiologically (Chap.13). The dynamic anatomy seen at gastroscopy and radiology tallies with the morbid anatomy described by Cunningham (l906), Forssell (l913) and Torgersen (l942). The part of the stomach on the caudal side of the "proximal sphincter", called the "distal antrum" or "pyloric channel", is the pyloric sphincteric cylinder.

According to Code and Carlson (l968) each terminal antral contraction (TAC) seen at gastroscopy, produces a diaphragm across the stomach with a central orifice. The size of the orifice depends on the strength of the contraction. Retropelled contents are forced with varying degrees of vigor through this orifice in an oral direction.

Comment: The diaphragm across the stomach with a central orifice again corresponds, in our view, to contraction of the left pyloric loop (Chap. 13). Not only gastric contents, but at times also gastric mucosal folds, are retropelled through the contraction ring of the left loop, by powerful contractions of the pyloric sphincteric cylinder (Chaps. 13, 36).

At gastroscopy Edwards and Rowlands (l968) found that ripples of contraction sometimes moved down the gastric wall to a well-defined ring where the large bag of the stomach joined the commencement of the "antral funnel". The ring often contracted to a narrow bore, at times obliterating the lumen, and could be mistaken for the pylorus. The true pylorus was situated at the end of the funnel. At times annular contraction waves with a frequency of 3 per minute moved long the "antrum" to the gastro-duodenal junction, propelling mucus. Sometimes the mucus would be retropelled from the funnel in an oral direction. The findings were ascribed to intermittent and possibly haphazard activity of the stomach due to the conditions pertaining at gastroscopy, such as the distension of the stomach, the stress of the subject, and the administration of sedative drugs.

Comment: In our view the well-defined ring at the commencement of the "pyloric funnel", which could be mistaken for the pylorus, again corresponds to the left pyloric loop, while the "pyloric funnel" corresponds to the sphincteric cylinder. The retropulsion of mucus through the ring is the result of normal contractile activity of the cylinder; normal retropulsion of barium occurs in the same way (Chap. 13). Blackwood (l969) pointed out that the correct interpretation of a ring structure in the pyloric region could present problems at gastroscopy, especially when it had an unusually large diameter, when a second ring was seen beyond it, or when radiology revealed a gastric lesion obviously distal to the ring structure visualized. In such cases it could be difficult to determine if one was dealing with the pyloric ring or with a different ring. In an attempt to improve the endoscopic evaluation of the pyloric region, he localized the pylorus by electrical potential difference (PD) measurements under direct gastroscopic vision. Of 9 studies, 7 revealed a significant PD change within 1.0 cm of the visualized ring, confirming the visual diagnosis of a normal pyloric ring. In all 7 cases the radiological appearance was normal. Two studies showed the PD change 3.0 to 4.0 cm beyond the visualized ring. In both, radiological abnormalities were evident in the stomach (one had an "antral" ulcer with narrowing, the other a "narrowed antrum"). These were regarded as cases of antral deformity mimicking the pylorus, i.e. false pyloric rings.

Comment: From the published radiographs of the 2 abnormal cases, it seems that the pyloric sphincteric cylinder was contracted in both. The "antral" ulcer in the first case was located within the cylinder. The rings visualized in these 2 cases must have been at the oral end of the contracted cylinder, i.e. in the situation of the left pyloric loop. The PD change 3.0 to 4.0 cm distal to the visualized rings confirms the above interpretation.

Of a total of l8 ring-like structures seen in the "distal antrum" at gastroscopy, Blackwood (l969) found 14 to be normal pyloric rings. Four of the l8 were "antral" deformities mimicking the true pyloric ring. It was concluded that about 4 out of 5 ring structures seen in the "distal antrum" would be pylorus, while about 1 out of 5 would be a different ring. The following criteria were suggested as aids in identifying rings in the distal antrum: the normal pylorus should be visualized distal to the occlusive portion of the "antral peristaltic wave" and remain patent and immobile between antral contractions. It should have the appearance of a sharply defined circumferential mucosal diaphragm projecting at nearly right angles to the antral wall. In cases of antral narrowing however, the wall would be observed to taper gradually to a narrowed area. An antral contraction wave might be seen to move smoothly in a caudal direction, distal to a ring-like structure. If mucosa distal to a ring was extruded proximally, it was likely that "antrum" was present distal to this particular ring. Blackwood (l969) finally defined the normal pylorus as a localized circumferential narrowing formed by a thin septum of mucosa with a small central aperture seen only, and remaining patent, between antral contractions, without mucosa or other landmarks being visualized distally.

According to Dagradi (l969), once the tipe of the gastroscope has been insinuated beyond the angulus, deep, rhythmic, sequential propagative waves of the "antrum" are commonly observed. These originate at the angulus, traverse the "antrum" and recede into the distance. On advancing the fiberoptic instrument, the waves are seen to terminate at a certain point of closure, where longitudinal mucosal folds are drawn together as if by a purse string. From this point a retrograde prolapse of bunched-up mucosa develops, somewhat resembling the opening of the petals of a flower bud; the point of closure has been likened to a rosette or "fleurette". Relaxation of the contraction ring follows, revealing the cavity of the "prepyloric antrum" and at its distal end the pyloric orifice. Normally the orifice is ring-like in configuration when seen head-on or oval if seen tangentially; at times it may be observed to contract or expand, changing slowly in diameter. Occasionally a false pyloric orifice may be seen which can be confusing. This usually occurs in association with a distal "antral" ulcer; the true nature of such a localized, unrelenting contraction ring becomes evident if the pyloric orifice can be observed distal to it.

Comment: The rosette-like point of closure again corresponds to contraction of the left pyloric loop, situated at the commencement of the pyloric sphincteric cylinder (Chap. 13). Retrograde prolapse or movement of mucosal folds during contraction of the cylinder is clearly visible radiographically (Chap. 13).

At endoscopy Kaye et al. (l976) found that the pylorus was frequently very narrow, but that it was usually not completely closed except during the terminal phase of an "antral" contraction.

Maratka (l984) mentioned that a congenital septum or an acquired fibrous septum (secondary to ulcer scarring) in the antral area might simulate the pylorus and could be called a "pseudopylorus".

Comment: The permanent "pseudopylorus" formed by a septum is obviously quite distinct from the normal intermittent, ring-like contractions of the left pyloric loop with its central aperture.

According to Varis (l989) endoscopy may fail to demonstrate motor disorders of the stomach, for instance in conditions such as diabetic gastroparesis.

Comment: One of the few shortcomings of endoscopy in the examination of the upper gastrointestinal tract is its inability to demonstrate the full range of gastric motor movements under physiological conditions. The very presence of an endoscope in the stomach with mechanical distension of the gastro-oesophageal junction, renders the examination unphysiological; so does air distension of the gastric lumen. Only movements ahead of the light source are seen and these cannot be correlated with those occurring more proximally.

Discussion #

In the light of the anatomy as described by Cunningham (l906), Forssell (l913) and Torgersen (l942), and the radiological forms of movement as described by Torgersen (l942) and Keet (1957), the sequence of events as seen at gastroscopy, can probably be stated to be as follows: once the tip of the gastroscope is beyond the angulus but some distance proximally to the pylorus (with the gastric lumen distended by air), the pyloric aperture is visualized and seen to be open most of the time. At times ripples of contraction are seen, and at times annular contraction waves with a frequency of 3 per minute (peristaltic waves) move along the distal corpus and sinus to a well-defined ring, formed by the left pyloric loop. On the caudal side of the ring longitudinal mucosal folds may be seen to recede into the distance and end at the pyloric aperture (Fig. 14.1).

Fig. 14.1. Contraction ring formed by left pyloric loop. On caudal side of ring longitudinal mucosal folds recede into the distance, ending at pyloric aperture

The region of the stomach between the ring (the left pyloric loop) and the pyloric aperture is the pyloric sphincteric cylinder. The ring may narrow (Fig.14.2) and contract to a narrow bore, through which mucus or at times mucosal folds may be retropelled. This indicates the stage of maximal contraction of the sphincteric cylinder as seen radiologically (Chap. 13).

Fig. 14.2. Further narrowing of ring (left pyloric loop). The region beyond the ring and between it and the pyloric aperture (not visible) is the sphincteric cylinder

As the contraction causes the lumen to "disappear", the event itself (except for the contraction of the left loop) is not visible gastroscopically. In this sense maximal contraction of the pyloric sphincteric cylinder causes, gastroscopically speaking, an event horizon in the distal stomach. After a few seconds the sphincteric cylinder (including its left loop) relaxes, revealing the pyloric aperture, which is seen to be open (Fig. 14.3).

Fig. 14.3. Pyloric aperture distal to the ring

Should the tip of the gastroscope be closer to the pylorus, the pyloric aperture itself may be seen to close or open to a certain extent, in the absence of contraction of the sphincteric cylinder (marked air distension of the lumen may prevent contraction of the cylinder). In this case the variation in size of the aperture is thought to be due to iris-like action of the mucosal folds (Chap.13).

References #

1. Blackwood WD. Pylorus identification. Gastroenterology l969, 57, 163-167.
2. Code CF, Carlson HC. Motor activity of the stomach. In: Handbook of Physiology, Sect 6: Alimentary Canal Vol 4: Motility, edit Code CF. Amer Physiol Soc, Washington DC l968, pp 1903-1916.
3. Cunningham DJ. The varying form of the stomach in man and the anthropoid ape. Trans Roy Soc Edinb l906, 45, 9-47.
4. Dagradi AE. The gastric antrum and the pyloric orifice. Gastroint Endosc l969, 16, 43-44.
5. Edwards DAW, Rowlands EN. Physiology of the gastroduodenal junction. In: Handbook of Physiology, Sect 6: Alimentary Canal Vol 4: Motility, edit Code CF. Amer Physiol Soc, Washington DC l968, pp 1985-2000.
6. Forssell G. Über die Beziehung der Röntgenbilder des menslichen Magens zu seinem anatomischen Bau. Fortschr Geb Röntgenstr 1913, Suppl 30, 1-265.
7. Johnson HD. The pylorus: its function and some surgical considerations. Proc Roy Soc Med l961, 54, 938-940.
8. Kaye MD, Mehta SJ, Showalter JP. Manometric studies of the human pylorus. Gastroenterology l976, 70, 477-480.
9. Keet AD. The prepyloric contractions in the normal stomach. Acta Rad l957, 48, 413-424.
10. Maratka Z. Terminology, definitions and diagnostic criteria in digestive endoscopy. Scand J Gastroenterol l984, l9, Suppl 103, 31-38.
11. Rider JA, Moeller HC, Puletti EJ. Gastroscopic observations of the dynamic anatomy of the antrum and pylorus. Gastroint Endosc l967, 14, 100- 101.
12. Schindler R. Gastroscopic observation concerned with the gross anatomy of the stomach: the musculus sphincter antri, observation of the position of the stomach, the mucosal folds. Amer J Dig Dis l936, 3, 149-153.
13. Torgersen J. The muscular build and movements of the stomach and duodenal bulb. Acta Rad l942, Suppl 45, 1-191.
14. Varis K. Diabetic gastroparesis (a review). Scand J Gastroenterol l989, 24, 897-903.