Interpretation of ileal biopsies: morphological features in normal and diseased mucosa

One of the advantages of flexible colonoscopy is that the terminal ileum ca n easily be reached and biopsied by an experienced operator, Thus, the path ologist will, with increasing frequency, receive ileal biopsies from patien ts who have or may not have ileal disease and it is therefore useful to hav e a good knowledge of the spectrum of ileal mucosal histology and pathology , of its normal function, and of the changes seen in different conditions. It is also desirable to be aware of diseases that occur less frequently. The ileal microscopic features are related to its absorptive function on th e one hand, and to nonspecific and specific defence mechanisms of the organ ism against potential hazardous components on the other. As a consequence t he mucosa features a constant physiological and controlled inflammatory pro cess. Part of the ileal mucosal structure is determined by the presence of the gut-associated lymphoid tissue (GALT) which plays a key role in discrim inating harmless nutrients and harmful pathogens. It will be important to distinguish this normal situation from alterations seen in infectious or inflammatory pathology. Further, because of the thera peutic implications, it is necessary that acute and chronic (idiopathic) in flammation are recognized. This will in general be possible by evaluating t he composition of the inflammatory infiltrate and the occurrence of epithel ial and mucosal architectural changes.