Neurosurgery

Table 21.1. Epidemiology.

Useful statistics

Number of patients surviving TBI in USA per year

1.3 million

Number of patients hospitalized with TBI in USA per year

230,000

Firearm-related TBI deaths in the USA during 1995

21,093

Economic burden during 1985

$37.5 billion

Even in concussive states without significant parenchymal damage, the concentration of extracellular K+ is increased fiftyfold. There is a direct relationship between extracellular potassium and mortality. Excess potassium in extracellular fluid (ECF) is sequestered by the glial cells, leading to swelling of the astrocytic footplates, cytotoxic edema, increased ICP and secondary ischemia. Disturbance of calcium homeostasis through inward movement of Ca++ results in metabolic cascades, with dire consequences. Elevated levels of calcium in cytosol results in multimeric transformation of proteins in mitochondrial outer membrane and formation of mitochondrial permeability transition pore (MPTP). MPTP allows abnormal concentrations of calcium in the mitochondrial matrix, disturbance of electron transport, formation of reactive oxygen species and activation of lipases, proteases and endonucleases, hence enhanced cell necrosis. Release of apoptogenic protein from mitochondria, along with intrinsic pathways, signal activation of apoptotic processes which result in programmed cell death [3]. Abnormal concentrations of Ca++ into the axons activates calpain-mediated cytoskeletal damage and axonal transport. The long-term effect of cytoskeletal damage is axotomy and Wallerian degeneration.

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