1. Morphology and fine structure of the brain
The morphological characteristics of brain death were examined in baboons and cats after artificial cerebral ischaemia. All animals showed autolytic changes in the brain, ischaemic neuronal changes, midbrain haemorrhages, focal necrosis of the brain-stem, demarcation at C 1/C 2 cord segment, and displacement of cerebellar tissue. Ultrastructural examination revealed extreme brain oedema, autolytic changes, and complete obstruction of capillaries by astrocytic and endothelial swelling and intravascular blebs. These data indicate that brain death develops in several stages. If the process starts in the supratentorial space it first leads to a breakdown of the cerebral circulation and to transtentorial herniation. As a result, midbrain haemorrhages develop and the infratentorial pressure begins to rise. The second stage is terminated by demarcation of the brain. The circulatory arrest is initially caused by venous compression but becomes irreversible when vascular obstruction develops.