Histopathological Characterization of Intra- and Extra-cranial Internal Carotid Arteries

The intracranial internal carotid artery (ICA) is well known to be a muscular artery that lacks an external elastic lamina. Elastic fibers are concentrated inside the internal elastic lamina of the wall of the intracranial ICA. We examined a portion where the external elastic lamina disappeared in the course of the ICA. We extirpated 32 intracranial ICA specimens from 50 cadavers. We made running specimens of the ICA every 3 mm and stained them using the Elastica van Gieson method and then investigated a portion where the external elastic lamina disappeared in the wall of the ICA. We also examined the intimal thickness of various portions of the ICA. We identified both the internal elastic lamina and the external elastic lamina in the petrous portion of the ICA in all cases. In the intradural portion of the ICA, the external elastic lamina was not recognized and only the internal elastic lamina was seen in all cases. In 31 of the 32 specimens (98%), the external elastic lamina disappeared in the horizontal portion of the cavernous portion of the ICA. The intimal thickness of the ICA was recognized in 23/32 specimens. The starting point of the intimal thickness approximated the portion where the external elastic lamina disappeared. The external elastic lamina of the ICA disappeared at the horizontal portion of the cavernous sinus, which was a site where intimal thickness was frequently observed. Changes in the elasticity of the wall of the intracranial ICA may therefore cause atherosclerotic changes in the ICA.