Brain abscess: This is a brain abscess in an advanced stage of development. It consists of a central area filled with purulent exudate surrounded by a fibrous connective tissue capsule that delimits the abscess. On the side of the abscess, the brain is edematous over the entire hemisphere. Thus a brain abscess acts as a mass in two ways: First, the abscess itself, like a tumor, is a space-occupying lesion and secondly, the swelling of surrounding brain substance creates further pressure.