Immunohistochemical detection of intracranial vasa vasorum: a human autopsy study

The existence of intracranial vasa vasorum supplying the larger vessels of the circle of Willis has long been debated. Much of this debate results from contradictory findings of microanatomic studies in a variety of nonprimate species. Recently, however, a growing body of evidence seems to suggest that in certain pathological situations, such as human intracranial atherosclerosis, vasa vasorum are present. In an effort to determine whether intracranial vasa vasorum are present in humans without clinical evidence of intracranial vascular disease, we studied the circle of Willis in five autopsy specimens using immunohistochemistry. Antiserum to the endothelial-specific antigen, Factor VIII, revealed staining of 10- to 20-microns vascular channels in the outer media and adventitial layers. Staining was present in the proximal carotid, middle cerebral (M1), and anterior cerebral (A1) arteries but could not be detected in M2 or A2 segments. Hematoxylin and eosin staining was additionally helpful in identifying the nuclear morphology of the endothelial cells lining these channels, as well as the presence of erythrocytes within them. We conclude that in nonpathological settings, endothelial-lined channels exist in the proximal intracranial vessels of humans. These vessels might represent intracranial vasa vasorum, which in turn might play a role in pathological conditions, such as atheroma formation, intracranial dissection, and vasospasm.