The Monro-Kellie doctrine states that the interior of the cranium is formed of three main components: blood, fluid and cerebral parenchyma. An increase in the volume of one or more components may increase the intracranial pressure (ICP). This doctrine also affirms that the skull cannot be expanded after the closure of the fontanels. Monro and Kellie's theory has been perfected during the last two centuries. This study leads to a new contribution that proves that even adults' consolidated skulls present volumetric changes as a consequence of ICP variations.