Morphological analysis of the pathogenesis of hypertensive cerebrovascular lesions: role of monocytes and platelets in intracerebral vessel occlusions.

We performed ultrastructural studies of intracerebral vessels in stroke-prone spontaneously hypertensive rats (SHRSP). The initial vascular lesions observed in the asymptomatic SHRSP were focal cytoplasmic necrosis in the outer layers of the media. Focal cytoplasmic necrosis progressed into wide-spread medial necrosis with time. In the SHRSP with cerebral infarctions we discovered that numerous monocytes adhered to the endothelium of the arteries having advanced medial damage. Following the adherence of the monocytes to the endothelium enormous amounts of plasma components entered and accumulated in the arterial wall. The accumulation of the plasma components, especially fibrin, thickened the wall, narrowed the lumen and resulted in occlusion with resultant cerebral infarctions. A lot of activated platelets are seen adhering to the endothelium of the capillaries and the venules around the cerebral infarctions. These results suggest that the monocytes and the platelets may be closely related to the occurrence of cerebrovascular occlusions. The occlusions may result in further cerebral blood flow reduction and continuous deterioration.