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Figure 15 11 brain edema this coronal section of the

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FIGURE 15-11Brain Edema. This coronal section of the cerebrum demonstrates markedcompression in the lateral ventricles(long arrows)and flattening of gyri(short arrows)from extensive bilateral cerebral edema. Edema increases intracranial pressure, leadingto herniation. (From Klatt EC:Robbins and Cotran atlas of pathology,ed 2, Philadelphia,2010, Saunders.)Three types of cerebral edema are (1) vasogenic edema, (2) cytotoxic (metabolic)edema, and (3) interstitial edema.Vasogenic edemais clinically the mostimportant type and is caused by the increased permeability of the capillaryendothelium of the brain after injury to the vascular structure. The selectivepermeability of capillaries that comprise the blood-brain barrier is disrupted.Plasma proteins leak into the extracellular spaces, drawing water to them andincreasing the water content of the brain parenchyma. Vasogenic edema begins inthe area of injury and spreads, with fluid accumulating in the white matter of theipsilateral side because the parallel myelinated fibers separate more easily. Edemapromotes more edema because of ischemia from the increasing ICP.Clinical manifestations of vasogenic edema include focal neurologic deficits,disturbances of consciousness, and a severe increase in ICP. Vasogenic edemaresolves by slow diffusion.376Incytotoxic (metabolic) edema, toxic factors directly affect the cellularelements of the brain parenchyma (neuronal, glial, and endothelial cells), causingfailure of the active transport systems. The cells lose their potassium and gainlarger amounts of sodium. Water follows by osmosis into the cells, so that the cellsswell. Cytotoxic edema occurs principally in the gray matter and may increasevasogenic edema.
Interstitial edemais seen most often with noncommunicating hydrocephalus.The edema is caused by transependymal movement of CSF from the ventricles intothe extracellular spaces of the brain tissues. The brain fluid volume increasespredominantly around the ventricles, with increased hydrostatic pressure withinthe white matter. The size of the white matter is reduced because of the rapiddisappearance of myelin lipids.HydrocephalusThe termhydrocephalusrefers to various conditions characterized by excess fluidin the cerebral ventricles, subarachnoid space, or both. Hydrocephalus occursbecause of interference with CSF flow caused by increased fluid production,obstruction within the ventricular system, or defective reabsorption of the fluid. Atumor of the choroid plexus may, in rare instances, cause overproduction of CSF.The types of hydrocephalus are reviewed inTable 15-15.TABLE 15-15Types of HydrocephalusTypeMechanismCauseNoncommunicatingObstruction of CSF flow between ventriclesCongenital abnormaAqueduct stenosisArnold-Chiari malformation (brain extension throughforamen magnum)Compression by tumorCommunicatingImpaired absorption of CSF within subarachnoid spaceInfection with inflamadhesionsCompression of subarachnoid space by a tumorHigh venous pressure in sagittal sinusHead injuryCongenital malformation

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