The Pyloric Sphincteric Cylinder in Health and Disease

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Chapter 15 (page 75)

Many authors failed to find evidence of a tonically contracted ring structure at the pylorus. Atkinson et al. (l957) were unable to demonstrate independent contraction of the pyloric ring; they found that the pylorus was normally relaxed and did not act antagonistically to phasic pressure waves. Andersson and Grossman (l965), Kaye et al. (l976), McShane et al. (l980), White et al. (l98l), Dooley et al. (l985) and Gaffney et al. (l987) found no convincing manometric evidence of a zone of tonically elevated basal pressure at the pylorus. McShane et al. (l980) stated that the pyloric sphincter remained patent under fasting conditions. Apart from a brief closure during contraction, the pylorus was always open, according to White et al. (l98l). Kelly (l983) and Gaffney et al. (l987) concluded that the evidence weighed heavily against the presence of a tonic sphincter at the pylorus.

Winans (l976) attributed the divergent results of manometric studies to differences in methodology and differences in position of the subjects examined. Whereas the human pylorus was easily identifiable as a gross anatomic structure, it eluded identification as a functioning sphincter. Winans (l976) called this a "sphincteric paradox", and referred to the pylorus as being "fickle". Adding to the confusion is the lack of agreement on the definition of a sphincter (Chap. 2) and its relation to a high pressure zone.

In determining the manometric features of the pylorus, none of the authors quoted, with the exception of Keet et al. (l978), referred to or took note of the muscular anatomy of the region as determined by Cunningham (l906), Forssell (l913) and Torgersen (l942) (Chap. 3). According to this concept the pyloric ring consists of an aboral thickening of the cylinder, and constitutes an inherent part of the cylinder both anatomically and functionally. The closest any of the authors came to the concept of a sphincteric cylinder at the pylorus, was the recognition of the "terminal antrum" as a functional unit by Carlson, Code and Nelson (l966), Code and Carlson (l968) and Shepard (l97l). However, the terminal antrum had not been defined in terms of muscular anatomy, whereas the sphincteric cylinder had.

The sphincteric mechanism at the pylorus will probably prove to be less paradoxical once the muscular component of the pyloric ring (the right pyloric loop) is no longer regarded as a separate structure, but is acknowledged to be an inherent part (i.e. the aboral end) of the pyloric sphincteric cylinder.


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