Histologic examination of CMV infection. (a) Haematoxylin and Eosin (H&E) staining for CMV. CMV-infected cells are indicated by yellow arrows. Cells infected with CMV are larger, with a thickened nuclear membrane and granular intracytoplasmic inclusions. Typical “owl’s eyes” or basophilic intranuclear inclusion bodies are representative of active CMV replicating nucleoprotein cores. (b) Immunohistochemistry (IHC) staining of CMV colitis. The use of IHC staining in histologic examination of CMV colitis can increase the diagnostic sensitivity. Typical IHC staining for enteric CMV is denoted by yellow arrows.