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FOCUS POINTS
The posterior fontanelle closes around 6 months of age and the anterior fontanelle around 12 to 18 months. Therefore, a slow increase in intracranial volume prior to cranial suture fusion can be compensated by an increase in head circumference.
Signs of intracranial hypertension differ in adults compared to children. Typical signs of high intracranial pressure (ICP) include increased irritability, headaches, decreased feeding, and morning emesis.
CMRO2 in children increases to 5.2 mL/100 g/min making them more susceptible to hypoxemia, contrary to neonates who have a lower CMRO2 at 3.5 mL/100 g/min making them relatively tolerant to hypoxemia.
By the age of 5, children have the normal adult volume of cerebrospinal fluid (CSF) which is 150 mL.
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CENTRAL AND AUTONOMIC NERVOUS SYSTEM
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The brain at birth is one-tenth of the body weight. Only one-fourth of neuronal cells that exist in adults are present in the newborn. By one year of age, the cells in the cortex and brain stem are developed completely. Myelinization and synaptogenesis are not complete until the age of 3. Primitive reflexes such as Moro reflex and grasp reflex disappear with myelination. At birth, the conus medullaris is at L3, and the dural sac ends at S1. By one year of age, the conus medullaris recedes to L1 and the dural sac shortens to S1. Unlike the central nervous system, the autonomic nervous system is developed at birth, though immature. The parasympathetic system is intact and fully functional in contrast to the sympathetic component which develops by 4 to 6 months of age.1–3
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The intracranial space has three components: brain tissue (80%), CSF (10%), and blood (10%). The Monro–Kellie hypothesis states that the sum of all intracranial components is constant (Figure 1-1). Specifically, an increase in volume of one of the components that causes an increase in intracranial pressure will result in a compensatory reduction in the other components to offset the change. The exception to this doctrine are neonates and infants since cranial sutures are open at birth. The posterior fontanelle closes around 6 months of age and the anterior fontanelle around 12 to 18 months. Therefore, a slow increase in intracranial volume prior to cranial suture fusion can be compensated by an increase in head circumference. However, acute dramatic increases in ICP can still cause herniation. Children with closed fontanelles have a higher risk of herniation than adults, due to a lower intracranial compliance and smaller cranial volume.4
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