The brain of the neonate weighs about 1/10 of the body weight. This is much larger than the adult, where it composes 1/50 of the body weight. The neonate’s brain grows rapidly, tripling in size by age one year. The neural plate appears at 3 weeks gestation and by 8 weeks neurons begin their migration to form cortical layers. This migration is complete by the 24th week. The brain is only about 25% complete at birth in relation to neuronal development. This development is complete by around age 1 (1). The central nervous system of the child is vastly different than the adult. The child’s CNS undergoes tremendous structural and anatomic change in the first two years of life (1). Children have a relatively low intracranial pressure (ICP) and have a remarkable ability to maintain a normal ICP in the presence of a change in intracranial volume due to the highly compliant nature of their cranium. This is accomplished because of the presence of open fontanelles and cranial sutures. The cranial sutures represent the spaces in between the major bones enclosing the brain, and the fontanelles are the various intersections of these sutures. The sequence of fontanelle closures occurs from the beginning of the second to third month. The posterior fontanelle is the first to close followed by the sphenoidal fontanelle, which should be closed completely by the 6th month. The mastoid fontanelle closes at around the 6th–18th month and the last fontanelle to close is the anterior at around 1–3 years of age (2). These articulating surfaces allow for the extremely compliant pediatric skull to expand and maintain a relatively normal ICP in the presence of a slow-growing tumor or fluid collection. Children, however, are not as easily capable of compensating for a rapid increase of a space-occupying lesion (2). Once these sutures and fontanelles close, the pediatric patient is at an increased risk for elevated ICP compared to the adult and is at a higher risk for herniation secondary to factors including the presence of a higher ratio of brain content to intracranial capacity (3).
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