In a subarachnoid hemorrhage model in the baboon, achieved through three cisternal blood injections with 1-day intervals, the cerebral arteries were dissected out 7 days after the first blood injection for electron microscopy All the animals showed ultrastructural changes in the cerebral arteries: two with severe, one with moderate, and three with mild alterations in the vessel walls. The most constant findings were seen in the muscle cells of the media layer. Fragmentation of the nuclei was frequently observed together with cytoplasmic vacuoles. Scattered groups or single degenerated muscle cells were also noted. In the intima the changes included rounding of the nuclei along with the appearance of cytoplasmic vacuoles. Desquamation or flattening of the endothelium and loss of tight junctions were encountered in some vessel areas. Degenerating mitochondria were a common finding.
