The ultrastructural changes of the microvasculature in the spinal grey matter were studied after impact injuries of varying severity in cats. Survival times ranged from 3 min to 6 h after injuries. The main vessels affected were capillaries and postcapillary venules. Perivascular haemorrhage and protein extravasation were present immediately after impact. Astrocytic foot processes could be swollen or shrunken and of increased electron density. The extra cellular space (ECS) was often distended with proteinaceous material. Some vessels showed an apparent increase in vesicles and small dense inclusions were seen in pericytes.

By 20–30 min after impact, a number of vessels at greater impact energies showed degenerative changes in organelles and endothelial gaps. The lumina of these vessels often contained plasma, platelets, red cells and occasional neutrophils. Similar changes were seen between 3 and 6 h and at this stage neutrophils and some monocytes were present in the perivascular spaces and neuropil. Endothelial balloons and pericytic dense inclusions were also seen.

It is suggested that initial events are mechanical, perhaps due to a rapid displacement of blood in venules followed by arterial hypertension (which commonly accompanies spinal cord impacts). Although initially many lumena are patent by 30 min there is a difference between the lesser and greater severities of impact.