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Chapter 1 (page 1)
There has long been disagreement about various aspects of the structure and function of
the "gatekeeper" (Greek pyloros, from pyle = gate and ouros = guard). In recent years the
problem has often been mentioned in anatomy, physiology, gastroenterology, radiology
and even in nuclear medicine. For instance, while referring to manometric and gastric
emptying studies, Schuurkes and van Nuenten (1984) pointed out that there was
considerable controversy as to whether a true pyloric sphincter existed in most species,
and especially in man.
According to Reeve (1981) many functional aspects of sphincters are poorly understood; the exact mechanism of control of the transfer of chyme from stomach to duodenum through the pylorus is still not clear. Malagelada (1983) states that controversy surrounds the motor activity and function of the antroduodenal junction; there is disagreement as to whether the pylorus functions as a separate unit or as an integral part of the distal antrum. Ehrlein et al. (l984) reiterate that pyloric motility is poorly understood, and according to Funch-Jensen (l987) there are many unsolved questions. Malagelada (1990) states that the stomach performs multiple functions with a deceivingly simple anatomy; this is regarded as the key to the investigator's frustration when trying to uncover its secrets. One source of the many controversies surrounding the pylorus may be species differences, according to Schulze-Delrieu et al. (1984).
In view of the divergent and sometimes conflicting views expressed, the aim of the present investigation is to examine, firstly, certain aspects of the anatomy and physiology of the gastroduodenal junction and secondly, to try and elucidate some aspects of the more common pathological conditions affecting the region.
In their investigations Camilleri et al. (l985) stated that radionuclide and manometric emptying studies provided closely interrelated physiological studies and might be regarded as complementary diagnostic tools in the investigation of some of these problems. It is our submission that radiographic studies, provided they are integrated with other modes of investigation, may similarly be regarded as an important and complementary diagnostic tool. It is recognized that radiology has certain demerits. For instance, it is hardly possible to quantify gastric emptying radiologically; barium sulphate in suspension, although non-soluble, non-absorbable and non-toxic, may separate from solids and liquids, rendering radiographic emptying studies of little value.
On the other hand upper gastrointestinal radiography has certain advantages. For instance, it displays anatomic detail exquisitely (Velchik et al l989). One may add that the same holds true for movements of the stomach and duodenum; these are clearly observable and recordable under physiological conditions in the intact stomach as well as after pharmacological modification. The absence of intraluminal tubes eliminates the possibility that they may modify physiological contractions or prevent sphincters from closing properly. Also, in experimental motility studies it has not been determined, as far as we are aware, what effects gastrostomy or duodenostomy has on motility. In radiology this is not a complicating factor.
There is a tendency, especially in physiology, to dismiss radiological investigations as "purely visual observations." This sounds rather illogical, as observation, by the nature of things, is a visual impression. On the other hand it would not be unreasonable to question the interpretation of these visual observations.
According to Texter (l963) radiology has been so successful in the demonstration of pathological processes, that there has been a tendency to overlook its application as an investigative aid in the exploration of normal physiological forms of movement. Edwards and Rowlands (l968) pointed out that various methods had been applied to the study of antral and pyloric movements and the transport of contents, but that each had its own limitations and interfered in some way with the mechanism. No single method had given a clear, acceptable picture, although radiology kept the best perspective.
The present investigation originated in, and was conducted from, the Radiological Department. The image or action observed, was regarded as a fact; its interpretation might be open to question. At all times radiological findings were critically evaluated and, where possible, considered in conjunction with other findings.
The designation "barium meal" appears to be something of a misnomer, as it implies the swallowing of solids, while a liquid is in fact imbibed. In view of the important differences between gastric emptying of solids and liquids, the term was considered to be ambiguous and was avoided where possible.
In descriptions of cases the clinical features were either not discussed or kept to a minimum, as the aim of the investigation is the discussion of anatomical, physiological and radiological features and of the pathogenesis.
In background descriptions and reviews of the literature the method followed was to present quotations in chronological order so as to obtain an historical perspective. Quotations were not identified by superscript number but by authors' names and dates for ready identification and a brief historical overview.
A number of intriguing entities will be encountered, such as the fickle pylorus and the sphincteric paradox of Winans (l976) (Chap. 15), the errant or wandering antrum (Chap. 2), and the Janus-like sphincteric mechanism, looking backwards (into the stomach) as well as forwards (into the duodenum) (Chap. 3). An event horizon is described (Chap. 14), which is perhaps another way of saying "we don't know." In addition the vagaries of the vagus nerves described by Skandalakis et al. (l986) (Chap. 8) will have to be faced.
But first of all it is necessary to consider some uncertain and almost undefinable concepts, viz. the "pyloric antrum," "sphincters," and "peristalsis."
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