Mills Ch22 Stomach

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CHAPTER 22:  Stomach

IM also shows changes in mucin core peptide expres- sion. Normally, the gastric surface epithelium expresses MUC5AC and smaller amounts of MUC1. In complete IM of the stomach, this expression is lost and the goblet cells stain for intestinal mucin (MUC2). Incomplete metaplasia may express mixtures of all types of mucin core peptides. There are also differences in mucin core protein expression between gastric cardiac metaplasia and Barrett metaplasia, but these are inconsistent and not particularly helpful for diagnostic purposes (26). Minor degrees of gastric IM are relatively common in persons in North America and elsewhere. The variants described above rarely exist as a pure entity, and mixtures of the various types within the same gastric foveola are encountered frequently. However, IM should never be con- sidered normal and almost always reflects some degree of gastric damage, usually from chronic gastritis. Less commonly encountered forms of metaplasia include subnuclear vacuolation (38) and ciliated meta- plasia (39). These changes all involve the pyloric mucus glands. Subnuclear vacuolation is not strictly a metaplas- tic change because it does not simulate the appearance of any other type of normal cells and probably represents a degenerative change secondary to gastritis or duodenal reflux. The vacuoles are clear on H&E sections and indent the nucleus. Ultrastructurally, they consist of a membrane- lined space derived either from endoplasmic reticulum or Golgi and probably contain nonglycoconjugated mucus core protein (40). Ciliated cells are found at the base of antral glands where there is superficial IM (37). The cause and significance of this change is not known. Pancreatic acinar metaplasia (41) may be present in up to 1.2% of gastric biopsy samples or 13% of gastrectomy speci- mens. The cells, which are indistinguishable from normal acinar cells, also produce lipase and trypsinogen. Seventy- five percent of cases are positive for amylase. Cells are pres- ent in nests and variably sized lobules scattered among the cardiac and oxyntic mucosae. Islets are not present. SPECIMEN HANDLING Gastric mucosa is delicate and should be handled with care. Tissue should be gently removed from the biopsy for- ceps and oriented before being placed flat on a supportive mesh, such as filter paper or Gelfoam. A variety of fixatives are suitable, depending on personal preferences, although routine formalin is suitable for most purposes. Sections are cut in ribbons, usually at two or three levels. For the best results, it is suggested that gastrectomy specimens be opened and pinned out on a corkboard or wax platform before being immersed in formalin and fixed overnight. If sections are taken directly from a fresh speci- men, they almost invariably curl up, resulting in irregular orientation of the final slide.

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