What are all the different abnormalities that could show up on a biopsy of a healthy appearing colon?

Here's some options: Microscopic colitis (lymphocytic colitis & collagenous colitis) is a colon biopsy diagnosis made typically in patients with atypical diarrhea, & is often linked to excessive use of nsaid's. Eosinophilic changes, evidence of "burned out" or early colitis, metaplasia/focal dysplasia, infection, are some other possible microscopic diagnoses that may manifest in an otherwise visually-normal colon.