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Chapter 11 (page 46)
In transverse sonographic sections the normal pylorus presents as a hypoechoic ring with
a central echogenic core (Chap 10, Fig 10.1). By comparing the sonographic image with
histological sections Blumhagen and Coombs (l98l) were able to show that the
hypoechoic ring corresponds to the muscularis externa layer of the wall, while the more
echogenic central core is formed by the mucosal and submucosal layers (including the
muscularis mucosae). By means of sonography the relative extent of the muscular and
mucosal/submucosal elements of the ring can be determined accurately in normal, living
subjects under physiological conditions.
In infants, Stunden et al (l986) found the maximum overall diameter of the normal
pyloric ring (presumably with the aperture patent) to be 13.0mm. The hypoechoic
muscular layer was 3.0mm in thickness. (The term "thickness" in sonography is
synonymous with "height" in microscopic anatomy). The minimum overall diameter
(presumably with the aperture closed) was 7.0mm, giving a radius of 3.5mm. In these
cases the muscle thickness was 1.0mm, and the mucosal/submucosal layer consequently
Stringer et al (l986) found the thickness of the mucosal/submucosal layer to vary from
2.5mm to 3.5mm in normal infants. According to Swischuk (l989) the muscularis
externa component of the ring usually measures 1.0mm in thickness and the
mucosal/submucosal component between 2.5mm and 3.5mm in normal infants. Minor
variations have been found by other authors (Chap 10).
Transverse sonographic sections of the contracted pylorus were obtained in 10 subjects
without gastrointestinal symptoms, ranging in age from one month to 73 years; in all a
typical "doughnut" appearance was seen (Fig 10.1). In all subjects it was clear that the
ring-like, hypoechoic outer muscular layer was equal to, or thinner than the inner,
echogenic mucosal/submucosal component of the ring. For instance, in a 5 year old child
the radius of the ring was 6.0mm, the thickness of the muscular layer 3.0mm, and that of
the mucosal/submucosal layer 3.0mm. In a 73 year old male the radius was 11.0mm, the
thickness of the muscle layer 5.0mm, and that of mucosa 6.0mm. It is concluded that,
during life, the muscular and mucosal/submucosal components of the ring are more or
less equal in height.
Many authorities look upon the pyloric ring as a sphincter (Chapter 2), implying that it is a
purely muscular structure. At the other extreme Cole (l928) considered it to be a muco-
membranous fold containing no muscular fibres at all. The present microscopic and
sonographic images show that the ring has both muscular and mucosal/submucosal
divisions. While the outer or peripheral part is formed by muscularis externa, the inner
part of this muscular rim is capped by a fold of mucous membrane. With microscopy the
height of the inner mucosal/submucosal division appears to be approximately one third
that of the muscular part. Sonography of the normal, living ring (which is more accurate
than microscopy in this instance, for reasons stated) shows that the muscular and
mucosal/submucosal divisions are more or less of equal height in children and adults; in
newborn infants the muscular division accounts for one-third, and the
mucosal/submucosal division for two-thirds of the height of the ring.
In view of these findings it appears improbable that the pyloric ring as such constitutes a
sphincter in the usually accepted sense.
- Blumhagen JD, Coombs JB. Ultrasound in the diagnosis of hypertrophic pyloric
stenosis. J Clin Ultrasound l98l, 9, 289-292.
- Cole LG. The living stomach and its motor phenomenon. Acta Rad l928, 9, 533-
- Edwards D. Some radiological aspects of pyloric disease. Proc Roy Soc Med
l96l, 54, 933-937.
- Edwards DAW, Rowlands EN. Physiology of the gastroduodenal junction. In:
Handbook of Physiology, Sect 6, Vol 4, Motility. Edit Code CF. American
Physiological Society, Washington DC, l968, l985-2000.
- Horton BT. Pyloric musculature with special reference to pyloric block. Amer J
Anat l928, 41, 197-225.
- Manning IH, Gunter GU. Prolapse of redundant gastric mucosa through the
pyloric canal into the duodenum. Amer J Path l950, 26, 57-73.
- Scott WG. Radiographic diagnosis of prolapsed redundant gastric mucosa into
the duodenum, with remarks on the clinical significance and treatment. Radiology l946,
- Stringer DA, Daneman A, Brunelle F, et al. Sonography of the normal and
abnormal stomach (excluding hypertrophic pyloric stenosis) in children. J Ultrasound
Med l986, 5, 183-188.
- Stunden RJ, Le Quesne GW, Little KET. The improved ultrasound diagnosis of
hypertrophic pyloric stenosis. Pediat Radiol l986, 16, 200-205.
- Swischuk L. Imaging of the Newborn, Infant and Young Child. Williams
Wilkins Co, 3rd Edit, Baltimore l989, pp 394-413.
- Williams I. Closure of the pylorus. Brit J Rad l962, 35, 653-670.
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