Infantile hypertrophic pyloric stenosis: myopathic type

New insights into the pathogenesis of infantile pyloric stenosis

Infantile hypertrophic pyloric stenosis (IHPS) is the most common surgical cause of vomiting in infants. Despite numerous hypotheses, the aetiopathogenesis of IHPS is not fully understood. Genetic, extrinsic and hormonal factors have been implicated in the pathogenesis of the disease. Furthermore, abnormalities of various components of the pyloric muscle such as smooth muscle cells, growth factors, extracellular matrix elements, nerve and ganglion cells, synapses, nerve supporting cells, neurotransmitters and interstitial cells of Cajal have been reported. Recently, genetic studies have identified susceptibility loci for IHPS and molecular studies have concluded that smooth muscle cells are not properly innervated in IHPS.

Interstitial cells of Cajal in the normal gut and in intestinal motility disorders of childhood

Interstitial cells of Cajal (ICCs) are pacemaker cells which are densely distributed throughout the whole gastrointestinal tract. ICCs have important functions in neurotransmission, generation of slow waves and regulation of mechanical activities in the gastrointestinal tract, especially for the coordinated gastrointestinal peristalsis. Therefore, a loss of ICCs could result in gastrointestinal motor dysfunction. In recent years c-kit labeling has been widely used to study pathological changes of ICCs in gastrointestinal motility disorders. Paediatric gastrointestinal motility disorders such as hypertrophic pyloric stenosis, Hirschsprung's disease, total colonic aganglionosis, hypoganglionosis, intestinal neuronal dysplasia, internal anal sphincter achalasia, megacystis microcolon intestinal hypoperistalsis syndrome have been reported to be associated with loss or deficiency of ICCs networks. This review describes the distribution of ICCs in the normal gastrointestinal tract and its altered distribution in intestinal motility disorders of childhood.

Interstitial cells of Cajal in human gut and gastrointestinal disease

This paper reviews the distribution of interstitial cells of Cajal (ICC) in the human gastrointestinal (GI) tract, based on ultrastructural and immunohistochemical evidence. The distribution and morphology of ICC at each level of the normal GI tracts is addressed from the perspective of their functional significance. Alterations of ICC reported in achalasia of cardia, infantile hypertrophic pyloric stenosis, chronic intestinal pseudoobstruction, Hirschsprung's disease, inflammatory bowel diseases, slow transit constipation, and some other disorders of GI motility as well as in gastrointestinal stromal tumors are reviewed, with emphasis on the place of ICC in the pathophysiology of disease.

Interstitial cells of Cajal in human gut and gastrointestinal disease

This paper reviews the distribution of interstitial cells of Cajal (ICC) in the human gastrointestinal (GI) tract, based on ultrastructural and immunohistochemical evidence. The distribution and morphology of ICC at each level of the normal GI tracts is addressed from the perspective of their functional significance. Alterations of ICC reported in achalasia of cardia, infantile hypertrophic pyloric stenosis, chronic intestinal pseudoobstruction, Hirschsprung's disease, inflammatory bowel diseases, slow transit constipation, and some other disorders of GI motility as well as in gastrointestinal stromal tumors are reviewed, with emphasis on the place of ICC in the pathophysiology of disease.

A quantitative study of the morphological and histochemical changes within the nerves and muscle in infantile hypertrophic pyloric stenosis

PURPOSE

The aim of this study was to quantify changes in dimensions of nerves and muscle and the proportionate expression of neural antigens in infantile hypertrophic pyloric stenosis (IHPS).

METHODS

Twenty specimens of pylorus from children with IHPS and age/sex-matched controls were examined using conventional histology and immunohistochemistry for a range of nerve and muscle antigens. The changes in the proportion of nerves expressing each antigen were quantified and statistically analyzed.

RESULTS

The longitudinal muscle was found to be hypertrophic and protein gene product 9.5-stained nerves appeared longer and thicker in the myenteric plexus and shorter in the longitudinal muscle layer in IHPS. The proportion of nerves that expressed neural nitric oxide synthase (nNOS) was found to be diminished in all the IHPS tissues examined. In the circular muscle and myenteric plexus, the proportion of nerves that expressed vasoactive intestinal polypeptide (VIP) and nNOS was almost identically diminished. The expression of calcitonin gene-related polypeptide and substance P was proportionately reduced in the myenteric plexus.

CONCLUSIONS

The results of this study represent the first quantitative analysis of nerves and muscle in IHPS. The muscle hypertrophy is not restricted to circular muscle layer. The changes in nerve morphology cannot be attributed to a dilutional effect of the muscle hypertrophy. The selective changes in nerve and ganglion morphology varies between tissue layers and neural antigen expressed. The findings of reduced proportions of nerves expressing, in particular, nNOS may shed some light on the etiology of this condition.

The pathology of infantile hypertrophic pyloric stenosis after healing

INTRODUCTION

Infantile hypertrophic pyloric stenosis (IHPS) is a common surgical affection of unknown etiology. The muscular hypertrophy is known to resolve within a few months after pyloromyotomy (PM). The pathology of IHPS has been studied extensively at the time of PM, but the fate of the pylorus after healing remains unknown.

MATERIALS AND METHODS

We had the rare opportunity to study two pyloric biopsy specimens obtained 4 months and 2 years (respectively) after an uncomplicated PM for IHPS. They were compared with the initial specimen in one case, with 26 other specimens of IHPS, and with five normal controls. Immunohistochemistry using the avidin-biotin complex (ABC) system was performed for S-100 and nerve growth factor receptor, as markers for the enteric nervous system, and for the tyrosine kinase receptor c-kit, as a marker for the interstitial cells of Cajal (pacemaker cells). NADPH-diaphorase histochemistry was performed as a marker for the neuronal enzyme nitric oxide synthase, which produces the inhibitory neurotransmitter nitric oxide.

RESULTS

In both cases of IHPS, after healing, the circular musculature was not hypertrophic. For all markers studied, the distribution appeared similar to that in the normal pylorus. In contrast, all specimens obtained at the time of PM displayed a severe reduction of the different markers in the hypertrophic musculature.

DISCUSSION

The pathological features observed in the circular layer in IHPS appear to resolve within a few months after PM. This suggests that the involvement of the enteric nervous system in IHPS might be milder than generally assumed. The etiology remains obscure, but our occasional observations may provide new insight into the pathophysiology of IHPS, and are in agreement with the excellent longterm clinical outcome for IHPS.

The ontogeny of the peptide innervation of the human pylorus, with special reference to understanding the aetiology and pathogenesis of infantile hypertrophic pyloric stenosis

Pyloric stenosis (PS) is a common condition in infancy, which is associated with smooth muscle hypertrophy that results in pyloric outlet obstruction. The author examines the ontogeny of the peptide innervation of the pylorus in fetal tissues and an experimental model in mice and evaluates the histochemical and morphological changes in the pylorus. The data suggest that PS is an intrauterine lesion that occurs by 12 weeks' gestation. This is associated with diminished nitric oxide in human tissues and reduced enzyme activity (resulting from a deficiency in an enzyme cofactor) in mice. Increased vasoactive intestinal polypeptide expression in pyloric myenteric ganglia may be an intrinsic mechanism for resolving this condition.

Hypertrophic pyloric stenosis: ultrastructural abnormalities of enteric nerves and the interstitial cells of Cajal

Dysfunction of pyloric inhibition has been implicated in the pathophysiology of hypertrophic pyloric stenosis. Normal inhibition likely is mediated by peptidergic enteric nerves and also may involve interstitial cells of Cajal (ICC). The authors used electron microscopy to qualitatively assess these structures in infants with pyloric stenosis and in normal controls. Pyloric muscle strips from five infants with hypertrophic pyloric stenosis, from three normal pediatric organ donors, and from three adults were examined. The following observations were made. (1) Muscle cells were primarily in a proliferative phase in pyloric stenosis and exhibited very few gap junctions between smooth muscle cells or ICC compared with the control specimens. (2) The circular muscle layer in pyloric stenosis was characterized by near absence of large granular vesicle-containing nerve fibers compared with the control specimens. (3) There were fewer nerve cell bodies in the myenteric plexus in pyloric stenosis, and the total number of ganglia was lower than that in control samples. (4) Interstitial cells of Cajal were almost completely absent in patients with hypertrophic pyloric stenosis, but there was a group of cells resembling ICC that was termed ICC-like cells. These cells may represent a failure or delay in the maturation process of the ICC. These findings show that there are significant structural abnormalities of the inhibitory nervous system in hypertrophic pyloric stenosis. The ontogenic origins and functional significance of these results require further investigation.

Abnormal distribution of nerve terminals in infantile hypertrophic pyloric stenosis

Smooth muscle biopsy specimens obtained from nine infants with infantile hypertrophic pyloric stenosis (IHPS) and from three controls were studied immunohistochemically with respect to the distribution of nerve terminals and neurofilaments. To label nerve terminals and neurofilaments, monoclonal antibodies (MAb) 171B5 and 2F11 were used, respectively. In all specimens of the control group, nerve terminals were numerous in both the myenteric plexus and the muscle layer. There were abundant neurofilaments in the myenteric plexus and a moderate number in the muscle layer. In all specimens of the IHPS group, the density of nerve terminals and neurofilaments was reduced in the muscle layer. In the myenteric plexus, there was no such reduction. The results indicate poor neuronal innervation of the muscle layer in the pylorus of infants with IHPS. This poor innervation may be related to the pathogenesis of pyloric stenosis and hypertrophy.

Intestinal pseudo-obstruction with deficient smooth muscle alpha-actin

We describe a 48-year-old woman with chronic constipation since early childhood who has an intestinal myopathy associated with a hitherto undescribed absence by immunostaining of smooth muscle alpha-actin confined to the intestinal circular muscle. There were no abnormalities in other contractile proteins (myosin, tropomyosin, filamin, caldesmon or desmin) and despite the abnormality of a contractile protein isoform in the circular muscle, no significant morphological changes were identified by light microscopy or ultrastructural examination. A possible developmental mechanism for the observed change is proposed. The use of specific antibodies to isoforms of contractile proteins may have potential value in the study of intestinal myopathies.

Nitric oxide synthase activity in infantile hypertrophic pyloric stenosis

BACKGROUND

Hypertrophic pyloric stenosis is a common infantile disorder characterized by enlarged pyloric musculature and gastric-outlet obstruction. Its physiopathologic mechanism is not known, but a defect in pyloric relaxation (pylorospasm) has been postulated. Nitric oxide is a mediator of relaxation in the mammalian digestive tract, raising the possibility that pylorospasm could be caused by a defect in nitric oxide production. Since neuronal nitric oxide synthase and NADPH diaphorase are identical, we used the NADPH diaphorase histochemical reaction to study the distribution of nitric oxide synthase in pyloric tissue from patients with infantile hypertrophic pyloric stenosis.

METHODS

We studied pyloric tissue from nine infants with infantile hypertrophic pyloric stenosis and seven control infants and children. Cryostat sections were processed for NADPH diaphorase histochemical analysis. A polyclonal tau antiserum was used to identify the enteric nervous system by immunohistochemical methods.

RESULTS

NADPH diaphorase activity was restricted to the enteric nervous system and blood vessels. In the pyloric tissues from the control patients, intense diaphorase activity was present in the nerve fibers of the circular musculature, in the neurons and nerve bundles of the myenteric plexus, and in some nerve fibers of the longitudinal musculature. In the pyloric tissues from patients with infantile hypertrophic pyloric stenosis, the enteric nerve fibers in the hypertrophied circular musculature were enlarged and distorted and did not contain diaphorase activity, whereas the activity in the myenteric plexus and the longitudinal musculature was preserved.

CONCLUSIONS

We suggest that a lack of nitric oxide synthase in pyloric tissue is responsible for pylorospasm in infantile hypertrophic pyloric stenosis.

Myenteric plexus neuropathy in infantile hypertrophic pyloric stenosis

The myenteric plexus and intramuscular nerve bundles in the circular muscle layer of the pylorus from 37 children with infantile hypertrophic pyloric stenosis (IHPS) obtained at pyloromyotomy were studied by light and electron microscopy and compared to six control cases without clinical evidence of IHPS. In certain IHPS cases degenerative alterations of the axons predominated. The axonal changes consisted of (1) severely increased variability of diameters with evidence of degeneration and regeneration of some axons, (2) accumulation of electron-dense bodies, lysosomes and pleomorphic membranous cytoplasmic bodies, (3) increase in the number of maloriented neurofilaments, and (4) aggregation of glycogen granules. Degenerative changes or immaturity of perikarya of neurons and glial cells in the myenteric plexus were not a significant feature. While axonal changes predominated in some IHPS cases there were severe changes of smooth muscle cells in others suggesting that a primarily neurogenic type of IHPS can be distinguished from a predominantly myogenic type. Although the etiology of the axonal changes in IHPS is not clear, it is suggested that they play an important role in the pathogenesis of pyloric stenosis and hypertrophy.