Cerebral edema, or increased swelling in the brain, can occur as the result of numerous etiologies, such as infection, inflammation, metabolic derangement, or neoplastic processes. Typically the brain has an undulating contour featuring crests or bumps called gyri, and troughs or grooves, called sulci. The mass effect produced by cerebral edema results in pushing or squeezing the brain against the unyielding bone of the calvarium. The cerebral hemisphere assumes a smooth surface contour, featuring flatten gyri and narrowed sulci, as it conforms to the smooth inner table of the skull.
For further study on this topic and others related to neuropathology and neuroanatomy, the following books come highly recommended, and a small portion of the proceeds (or any Amazon purchase through these links) help with expenses of hosting this site:
Adventures in Neuropathology 