Chapter 13 (page 60)

The Pyloric Sphincteric Cylinder in Health and Disease

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Chapter 13 (page 60)

Interplay Between Left and Right Loops

Radiologically it appears if contractions of the left and right pyloric loops start simultaneously. However, the degree or intensity of contraction of the two loops appears to vary. During a pyloric cycle the left loop (which is adjacent to the stationary peristaltic wave) may contract maximally, bisecting the lumen (Fig. 13.13). At this stage the right loop may be incompletely contracted, surrounding a central aperture (the patent pyloric aperture). Under these circumstances liquid contents flows into the duodenum. Propulsion into the duodenum is enhanced if contraction of the entire sphincteric cylinder now ensues.

Fig. 13.13. Left pyloric loop (arrow) tightly contracted, almost bisecting lumen. Right loop (i.e. muscular part of pyloric ring) not contracted and aperture patent

This process is well seen during gastric emptying of liquid barium, as illustrated in the following representative case:

Case J.V., male aged 35 years. A motor quiescent stage was awaited in which the stomach and duodenal bulb were filled; as often happens in the absence of motor activity, filling of the remainder of the duodenum was in abeyance. The pyloric sphincteric cylinder was relaxed; the aperture was patent, measuring 10.0 mm in diameter (Fig 13.14A). When gastric motor activity resumed, a stage was awaited at which the first peristaltic wave became stationary, immediately prior to contraction of the cylinder (Fig 13.14B). Immediate filling of the remainder of the duodenum ensued. The pyloric aperture widened marginally, now measuring 12.0 mm in diameter.

A B

Fig. 13.14. A,B. Case J.V. A Motor quiescent phase. Pyloric sphincteric cylinder relaxed. Pyloric aperture patent. Duodenal bulb filled. B Peristaltic wave stationary and commencing contraction of left pyloric loop (arrow). Filling of remainder of duodenum. Marginal widening of aperture.

This and similar cases show that gastric emptying of liquid barium may be associated with arrival of a peristaltic wave at the commencement of the sphincteric cylinder. Arrival of a peristaltic wave here may also be associated with marginal further widening of the already patent pyloric aperture.

On the other hand the right loop may be fully contracted, closing the pyloric aperture, while the left loop is incompletely contracted, surrounding a central aperture. In this instance contraction of the sphincteric cylinder is associated with orad movement of barium, i.e. retropulsion. (An example of retropulsion is to be described in Case G.O., under "Mucosal Movements").

A	B
`Fig. 13.14. A,B. Case J.V. A Motor quiescent phase. Pyloric sphincteric cylinder relaxed. Pyloric aperture patent. Duodenal bulb filled. B Peristaltic wave stationary and commencing contraction of left pyloric loop (arrow). Filling of remainder of duodenum. Marginal widening of aperture.`