Anatomy

There are usually two medial and four or five lateral lenticulostriate arteries (Rosner et al., 1984) (Fig. 31.1). and these divide to give an average of 26 branches on penetrating the brain (Marinkovic et al.,1985a)(Fig. 31.2). The lateral lenticulostriates are twice the diameter of the medial ones and are longer. The medial lenticulostriates supply the more medial deep MCA territory (lateral globus pallidus, medial putamen, whereas the lateral lenticulostriates supply the lateral putamen and external capsule, and the upper internal capsule (Herman et al., 1963) up to the white matter of the coronaradiata (De Reuck, 1969; Donzelli et al., 1998). Up to 50% of penetrating arteries arise from a common stem (Fig. 31.3), and occasionally a single common stem gives rise to all lenticulostriates (Umansky et al., 1985; Vincentelli et al., 1990). The ramification zone of the lenticulostriates has been measured on a methacrylic resin cast of the perforating arteries (Marinkovic et al., 1985b). On the basis of these measurements, occlusion of a medial lenticulostriate or of the distal branches of a lateral lenticulostriate artery is likely to give an infarct within the accepted limit of a lacunar infarct (15mm diameter). Occlusion of a single lateral lenticulostriate proximally however, or of a common stem giving rise to two or more lenticulostriates, is likely to give an infarct considerably larger than the accepted dimensions of a lacunar infarct.