MODULE 10
THE POSTERIOR ARTERIAL SUPPLY to the BRAIN
- - - This part of the system is fed by the two vertebral arteries which join at the border between the medulla and pons to form the basilar artery (Figure 10-3 , Blumenfeld's Figure 10.3) . This is the only example we can think of in the body in which two arteries join as they pass to the periphery to form a single, larger vessel - and one can't help but wonder if the "purpose" is to insure a constant blood supply to that relatively small part of the brain (the brainstem) the function of which is essential for the maintenance of life. In the lower part of Figure 1-37 the left vertebral has been cut just below the point where it joins the right vertebral to form the basilar artery; just above this, the basilar can be seen running between the basilar pons and the base of the skull. The basilar artery ends by giving off two branches, the superior cerebellar and posterior cerebral arteries (Figure 10-3 , Blumenfeld's Figure 10.3) . The oculomotor nerve passes between these two vessels as it exits from the brainstem; this is an important relationship, and for another view of it see Blumenfeld's Figure 13.2.
- - - The posterior cerebral artery supplies the medial surface of the occipital lobe and the basal surface of the occipital and temporal lobes. In addition, like the anterior cerebral, it sends branches around the "corner" on to the lateral surface of the hemisphere (Figure 10-4, Figure 10-5 , Blumenfeld's Figures 10.5 & 10.9). Once again look at the sections called up using Figure 10-6 and the maps given in Blumenfeld's Figures 10.5 & 10.9 to confirm the region of the hemisphere supplied by the posterior cerebral artery. Then read about watershed zones starting on page 378 in Blumenfeld and illustrated in his Figure 10.10.
- - - The remaining branches of the posterior circulation are primarily concerned with supplying blood to the brainstem (medulla, pons, midbrain) and cerebellum, but it is not surprising that there is some overlap between anterior and posterior systems at the border between the midbrain and the thalamus. The most obvious examples are the thalamogeniculate and thalamoperforant arteries. The former come off the posterior cerebral artery as it wraps around the midbrain and supply the geniculate nuclei and much of the caudal thalamus (Blumenfeld's Figure 10.8A ). The latter (thalamoperforants) are called thalamic penetrating branches in our views: they come off both the posterior communicating artery (Figure 10-3) and the posterior cerebral artery (Blumenfeld's Figure 10.8).
- - - The basic plan of the blood supply to the brain stem is the same at all levels and is illustrated in Figure 10-2. The long circumferential branches are derived, in ascending order, from the posterior inferior cerebellar artery, the anterior inferior cerebellar artery, the superior cerebellar artery and the posterior cerebral artery. Blumenfeld covers the blood supply to the brainstem in his Chapter 14, starting on page 607. While his terminology is slightly different from ours the sections in his Figure 14.20 are in general agreement with ours, which can be called up using Figure 10-7.
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