Pathology General Aspects

The severity and extent of the pathologic process depends chiefly on the severity and duration of the hypoxic event, on the body temperature, and on the blood glucose concentration. Hyperglycemia aggravates the ischemic damage whereas hypothermia protects the brain.

The cerebral pathology is distinguished by (a) selective neuronal necrosis and (b) selective regional vulnerability.

In selective neuronal necrosis, a lack of oxygen from any cause affects first, and usually, only the neurons. Necrosis of the glial cells, axons, and myelin (pan-necrosis) occurs in severe and protracted hypoxic-ischemic events.

Selective regional vulnerability determines the anatomic distribution of the lesions. Most vulnerable are the hippocampus, the neocortex, the cerebellar cortex, the thalamus, and the basal ganglia. The hypothalamus, the brainstem, and the spinal cord are the least vulnerable. In the hippocampus, the pyramidal neurons in the CA1 zone (Sommer's sector) are primarily affected (Fig. 3.1); in the neocortex, laminae 3, 5, and 6; in the cerebellum, the Purkinje cells;. in the thalamus, the anterior and dorsomedial nuclei; and, in the basal ganglia, the spiny neurons. Carbon monoxide poisoning has an affinity for the iron-rich globus palli-dus and the reticular zone of the substantia nigra.

Gross features range from patchy congestions of gray structures in the very acute stage, through soft, spongy cortex in the subacute stage, to atrophic sclerotic

FIGURE 3.2

Acute ischemic-hypoxia. A few days' survival following myocardial infarct and cardiac arrest in a 62-year-old man. Coronal section shows patchy congestion in the cerebral cortex.

FIGURE 3.2

Acute ischemic-hypoxia. A few days' survival following myocardial infarct and cardiac arrest in a 62-year-old man. Coronal section shows patchy congestion in the cerebral cortex.

cortex in the chronic stage. The deep gray structures and the hemispheric white matter are variably atrophic, and the ventricles are dilated in chronic cases (Figs 3.2. 3.5, 3.7, 3.8 and 3.9 ).

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