Study of the elastic skeleton of intracranial arteries in animal and human vessels by scanning electron microscopy.

We studied the elastic skeleton of major cerebral arteries in rats, monkeys, and one human using scanning electron microscopy after hot formic acid extraction followed by freeze-drying. For comparison, we also examined the thoracic aorta and femoral artery of rats. The cerebral arteries of rats had one distinct internal elastic lamina connected to the thin adventitia with sponge-like medial elastic tissue. This internal elastic lamina had fenestrations, which we found to be less frequent in cerebral arteries than in extracranial arteries, and fold-like protrusions into the lumen. This finding has not been recognized before. Such protrusions were more prominent in cerebral arteries than in extracerebral arteries. At the apical intimal pad, the internal elastic lamina appeared to be continuous, making a honeycomb-like structure. The folds and fenestrations were numerous at the apex. There were no essential differences among species. Our study shows that the internal elastic lamina is not a simple sheet but part of the complicated architecture of the elastic tissue of the vessel wall. These differences in the elastic skeleton, including fenestrations and fold-like structures, in various sites of different arteries may explain the development of various localized vascular diseases.