The Pyloric Sphincteric Cylinder in Health and Disease



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Chapter 11 (page 44)

Chapter 11

Anatomy of the Pyloric Ring

In fresh specimens a narrow (3.0mm to 4.0 mm) annular thickening, the pyloric ring, is felt in the wall of the gut at the gastro-duodenal junction. At laparotomy it may be difficult to palpate (Edwards and Rowlands l968), due to the effects of muscle relaxants administered during anaesthesia. On radiographs taken during the motor quiescent phase of the interdigestive myoelectric complex, the ring presents as a deep, clearcut, annular indentation separating the barium in the lumen of the stomach from that in the duodenum (Fig 11.1).

Fig. 11.1. Radiograph of normal pyloric ring (arrow) in motor quiescent phase of interdigestive myoelectric complex

Radiographic Anatomy

Edwards (l96l) found the length of the ring, as measured on radiographs, to vary between 1.0mm and 12.0mm; the mean length was 1.7mm. It was not stated whether these measurements were taken during motor quiescent or during contraction phases. (Comment: the term "width" is preferred to "length" as used by Edwards. Normally, the width of the pyloric ring may vary, depending on the stage of contraction of the pyloric sphincteric cylinder, as described in Chapter 13).

Present Investigations

The width and height of the pyloric ring, and the diameters of the pyloric aperture, sphincteric cylinder and duodenal bulb, were measured on radiographs of 10 adult subjects, taken at a time when no visible motor activity was evident, i.e. during the motor quiescent phase of the interdigestive myoelectric complex (Fig 11.2, Table 11.1). All subjects had been referred for radiographic examination because of vague upper abdominal symptoms. In none could an organic lesion be demonstrated; clinically and radiologically the stomach and duodenum were considered to be normal in all. The mean width of the ring was 4.7mm and the mean height 11.1mm; the depth was approximately the same on the greater and lesser curvature sides.

Fig. 11.2. Diagram of pyloric ring in motor quiescent phase. W, width; H, height; DB, duodenal bulb; PA, pyloric aperture; PSC, pyloric sphicteric cylinder

The inner margin of the ring surrounds the pyloric aperture, i.e. the opening by which the lumen of the stomach communicates with that of the duodenum. In the motor quiescent phase the diameter of the aperture varied from 5.0 to 13.0mm, with a mean of 8.7mm. The mean diameter of the sphincteric cylinder was 57.1mm, and the mean diameter of the duodenal bulb 35.8mm. (Comment: Owing to magnification factors the real measurements will be approximately four-fifths of the figures given).

Table 11.1 Radiographic measurements during the motor quiescent phase of the interdigestive complex
CaseWidth of ring (mm)Height of ring (mm)Diameter Aperture Diameter sphincteric cylinder (mm)Diameter duodenal bulb (mm)
14.015.011.060.045.0
25.013.010.061.038.0
36.011.06.054.026.0
44.011.06.064.030.0
57.014.011.050.040.0
68.013.013.074.040.0
73.05.06.060.050.0
83.011.010.040.035.0
94.06.09.045.026.0
103.012.05.063.028.0
Average4.7011.18.757.1 35.8

Conclusion

It is concluded that the pyloric ring causes an appreciable constriction of the lumen at the gastroduodenal junction. Furthermore it is seen that the pyloric aperture is patent during the motor quiescent phase.

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