Brain herniation is the movement of a part of the encephalon through an intracranial orifice. It is a complication of the rapid increase of intracranial tension following an edema or a hemorrhage, an expansive and rapidly growing process found in certain types of tumors or cerebral thrombophlebitis which prevents normal blood circulation. It may correspond to the sliding of a cerebral hemisphere under the membrane that lies between the hemispheres, the falx cerebri: this is called subfalcine herniation. Two other types of herniation are more serious : the temporal herniation, where the lower part of the temporal lobe causes compression, or downward cerebellar herniation also called tonsillar herniation. Symptoms range from headaches to coma with a risk of death. Note that the term herniation alone is a process signifying the onset of labor.