Imaging of Acquired Cerebral Herniations

The cranium provides protection for the brain against external forces, The brain is suspended in the cerebrospinal fluid (CSF) and supported by the skull and dural septa, which divide the cranial cavity into compartments and prevent excessive movement of the brain [1]. The unyielding cranium is a closed system and hence there is a fixed volume for the brain, CSF, and blood vessels and very little room for expansion in the face of increased intracranial volume and pressure. The brain is essentially incompressible (its shape can be altered, but its volume is basically constant); therefore, the vascular and CSF spaces must compensate for alterations in intracranial volume because of mass lesions or cerebral edema [2,3]. Unfortunately, this capacity is very limited, and when it is exceeded, cerebral displacement and herniation result. Cerebral herniation is the displacement of brain tissue from one compartment to the other. Of course, there are numerous variables that influence the degree of herniation and its untoward neurologic effects, such as the location of the mass, the volume of the mass, the intracranial pressure, the rate at which alterations in pressure and volume develop, brain atrophy, and individual anatomical variations.