atrophic gastritis treatmentatrophic hyperplastic gastritischronic atrophic gastritismultifocal atrophic gastritisdiffuse atrophic gastritisatrophic gastritis reversibleatrophic antral gastritismild atrophic gastritisautoimmune chronic atrophic gastritisatrophic body gastritissevere chronic atrophic gastritisatrophic gastritis pathology outlines