Injury-Induced Cell Death: Necrosis
The most common cause of necrosis is ischemia. Other causes include mechanical injury (contusion
Fig. 4.13a-c. High pressure hydrocephalus. a Increased brain volume and flattened gyral crests; b extreme periventricular glio-
necrosis), toxic agents (formic acid in methyl alcohol), heat (thermocoagulation), freezing (cryosurgery), infections (poliovirus), and overexposure to ultrasound. Each case, however, involves the action of additional factors independent of the type of primary traumatic event. Chief among these factors are free radicals and nitric oxide (NO). Reaction products of NO and O2, including potent oxidizing molecules such as peroxynitrite and nitrogen dioxide, can be more toxic than NO itself.
The type of brain necrosis depends in large part on the duration of local circulatory arrest:
1. Transient ischemia only destroys neurons and oligodendrocytes, inducing incomplete necrosis or selective neuronal necrosis (Scholz 1953).
2. Prolonged ischemia, termed "infarction," gives rise to complete necrosis of all tissue components.
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