Abstract
It is well known that some types of vertigo and dizziness are caused by impairment of the vertebro-basilar systems (VBS). And, it is thought that decreases or lateral differences in blood flow in the inner ear and/or brainstem can induce an imbalance in the equilibrium function and provoke a change in the vestibular excitability in the brainstem.
The vascular architecture and hemodynamics were estimated to solve the mechanism of vertebro-basilar dysfunction with some basic findings in the anatomical, morphological and hemodynamic studies of the vestibular and cochlear nuclei in the brainstem. The results are:
(1) Many variations in the VBS in human posterior circulation were seen. The VBS is the only parallel vasculature in the skull. The anterior inferior cerebellar artery (AICA) originates symmetrically from the basilar artery (BA) and the posterior inferior cerebellar artery (PICA) originates from the vertebral artery (VA) in about 60% of the cases. Measurement of VAs showed that the left VA was larger across the inner diameter than the right VA.
(2) The human vestibular nucleus (VN) area is supplied by some terminal arteries (the penetrating branches in the brainstem), one of which is the median pontine branch from the BA and the others penetrate the brainstem straight and from parallel arrangements with each other in the brainstem. The VN area has fewer circumferential branches and less development in the collateral circulation than the cochlear nucleus.
(3) No age-related changes in blood velocity are seen in the human BA. However, the blood velocity in the VA, which has the parallel arrangement, becomes bigger. The cross section of the VA does not decrease, and the arterial wall shows an outer thickness; arteriosclerotic change is "Kalk-Rohr"-like. Therefore, the area supplied by the VA is easily affected by hemodynamic changes.
These findings and experiments simulating the VBS (shown in a latter chapter) suggest that hemodynamics in the human posterior circulation differ from those in the anterior circulation.
