Emboli Enter Penetrating Arteries of Monkey Brain in Relation to Their Size

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Abstract
Background and Purpose Controversy exists regarding whether lacunar infarction is due to embolism or whether it is always due to lipohyalinosis of small penetrating arteries. We hypothesized that emboli can enter penetrating arteries in relation to the blood flow to these arteries and to the diameter of the emboli. Methods We injected agarose spheres of three different mean diameters (31±4, 68±14, and 92±28 μm [n=50 for each]) into one internal carotid artery of 3 monkeys for each sphere size (total, n=9 monkeys). After injection of spheres, monkeys were killed, the brains were removed and fixed in formalin, and serial hematoxylin and eosin sections of three coronal sections of the cerebrum were examined by light microscopy. Sphere diameter (n=25 for each territory and sphere size) and distribution in circumferential and penetrating artery territories were measured with the use of an image analyzer. Corrections were made for shrinkage of spheres during fixation and for the effect of random sampling of 10-μm sections through spheres of different diameter. Results Mean numbers of spheres for each size were significantly higher in circumferential than penetrating artery territories ( P <.05, t test). When correction was made for the volume of brain supplied by each territory, there was no significant difference in the number of spheres in circumferential versus penetrating artery territories for the two smaller sphere sizes. For spheres of mean diameter of 92 μm, significantly more spheres entered circumferential rather than penetrating artery territories ( P <.05, t test). The percentage of the total number of spheres that entered penetrating artery territories was 5%, 6%, and 1.4% for beads of 31±4, 68±14, and 92±28 μm mean diameter, respectively. Conclusions Small emboli can enter penetrating arteries and could therefore produce lacunar infarction. The majority of emboli, however, enter circumferential arteries. The larger the emboli, the more likely that they will enter circumferential arteries rather than penetrating arteries.