The Pyloric Sphincteric Cylinder in Health and Disease

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Chapter 23 (page 108)

By means of light microscopy Belding and Kernohan (l953) studied the myenteric plexuses and thickness of the muscle layers in normal controls, in 9 cases of IHPS and in 5 cases of adult hypertrophic pyloric stenosis (AHPS). In both IHPS and AHPS the number of myenteric ganglion cells and myenteric nerve fibre tracts per unit area of muscle tissue showed a real decrease in the pyloric region, while it remained quantitatively normal in the remainder of the stomach and in the duodenum. A constant finding was that the majority of myenteric ganglion cells in the pyloric region also showed degenerative changes, consisting of indistinct nuclear membranes, fragmentation or disintegration of the nucleolus, and disintegration of the cytoplasm with loss of cell membranes. Such changes were not present in the myenteric ganglion cells in the remainder of the stomach and in the duodenum, nor were they evident in normal controls. These pathological changes could be due to exhaustion caused by excessive vagal stimulation. According to these authors thickening of the muscularis externa in the normal stomach commences at a point just below the gastric incisura, extends to the pyloro-duodenal junction, and consists mainly of an increase in thickness of the circular musculature. In IHPS and AHPS the circular muscle of the pylorus was 2 to 4 times as thick as in normal controls, while it remained normal, or showed only a slight increase in thickness, in the remainder of the stomach and the duodenum. Microscopically the hypertrophied circular muscle of IHPS and AHPS had an irregular pattern with muscle fibres running in all directions, resembling a leiomyoma. The disorganization of muscle fibres was not evident in the stomach above the stenosed area and in the duodenum, neither was it seen in the normal stomach. It was unlikely that the ganglionic changes were secondary to the muscle hypertrophy and there appeared to be primary changes in both the myenteric ganglia and the musculature.

Carter and Powell (l954) recorded 12 examples of pyloric stenosis in parent and child, and drew attention to the increased risk of the disease in offspring of parents who were themselves affected. It was thought that genetic predisposition was a strong probability in the pathogenesis. However, environmental factors also had to be considered.

McKeown and MacMahon (l955) traced 112 adults who had been operated upon for IHPS in infancy. They had 29 children, none of whom exhibited pyloric stenosis. This and several other series examined by these authors, led them to conclude that a simple genetic hypothesis was unlikely. The condition could more plausibly be attributed to early postnatal environmental factors.

Friesen et al (l956) also using light microscopy, studied the myenteric nerve plexuses in normal controls and in l9 infants with IHPS. In the normal foetus at 12 weeks' gestation, the myenteric nerve layer of the pylorus appeared as an almost continuous layer of immature, completely undifferentiated nerve cells with little, if any segmentation into nests or plexuses. At 14 to 16 weeks there was a tendency towards elongated plexuses of cells which were still undifferentiated. At 26 weeks the myenteric layer showed organization into definite plexuses which contained, in addition to the undifferentiated cells, some cells with vesicular nuclei. Shortly after birth more mature cells appeared in the plexuses. Mature ganglion cells with abundant cytoplasm, prominent cell and nuclear membranes with nucleoli first appeared between the second and the fourth week after full-term gestation. The shift was toward differentiation so that recognizable mature ganglion cells were present in the normal pylorus from one to 5 months, with only a few undifferentiated cells being visible. In IHPS, at 4 to 8 weeks after birth, the plexuses contained no mature ganglion cells, having a cellular development similar to that of a normal pylorus several weeks earlier in age. It was concluded that failure of development or maturation of the ganglion cells was present, rather than degeneration of the cells as had been postulated by previous authors. The "degenerated" or "disintegrated" appearances previously described were probably cells which had never developed completely.

Roberts (l959) studied normal controls and biopsy specimens obtained at pyloromyotomy in 25 cases of IHPS. True hypertrophy of both longitudinal and circular muscle layers was evident, which he ascribed to overwork. The myenteric plexuses were examined for the quality and quantity of neural elements, i.e. nerve cells, supporting cells of Schwann and nerve fibrils. In IHPS the constituent cells had less cytoplasm and were more tightly packed than in normal controls, with fewer well-differentiated nerve cells in evidence. The size of ganglia tended to be smaller and the intervals between them greater than in normal specimens. The large continuous sheets of ganglia seen in the normal pylorus were absent, and it was concluded that there were quantitative as well as qualitative changes in the myenteric ganglia in IHPS.

Rintoul and Kirkman (l961) studied the morphological appearance of the myenteric ganglion cells and the structure of the nerve fibre tracts in biopsy specimens in 38 infants with IHPS. With silver staining two distinct ganglion cell types were recognized: (1) Type I Dogiel cells, showing a marked affinity for silver. While they were present in the control specimens, they were absent or virtually absent from the pyloric ganglia in cases of IHPS; this suggested that these cells were either congenitally absent, or that they had degenerated. (2) Type II Dogiel cells, which were less argentophylic. These were present and uniformly distributed throughout the myenteric ganglia in both the control and biopsy material. No clear evidence of degeneration of ganglion cells, such as had been described earlier, was found. However, it was admitted that early degenerative changes might not have been revealed by the silver staining process.

Friesen and Pearse (l963) studied the histological and histochemical features of the pyloric ganglion cells in biopsy material in 15 cases of IHPS; post-mortem studies were done in 2 additional cases. In IHPS the ganglion cells in the pylorus were not arranged in an evenly dispersed layer between the longitudinal and circular musculature. Cells were present in clumps within the thin longitudinal musculature, with infrequent extensions into the underlying circular layer. While numerous cells were present, few were large, mature cells, the majority being small and immature; these cells were enzymatically active and the histological appearances were not those of degenerated or dead cells. However, there was lack of mitochondrial and other oxidative enzymes characteristic of the mature cell. The features suggested arrest of the normal development of ganglion cells in the pyloric area. Mature ganglion cells containing numerous mitochondria were present in large numbers in the gastric wall above the pylorus in cases of IHPS, as well as in the pylorus in normal stomachs. The results supported the theory that motor acitivity such as pylorospasm preceded the development of hypertrophy of the pyloric circular musculature.

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