Anatomy of penetrating arteries

Penetrating arteries arising from the large arteries in the circle of Willis supply the basal ganglia, medial temporal lobe, and brainstem (panel a). Few other examples exist in the human body in which very small arteries arise directly from a large caliber artery. This unique anatomy makes these small arteries susceptible to central hemodynamics. In fact, the usual 90-degree angle T-bifurcation promotes intimal thickening at the origin of these arteries as they emerge from their parent artery. As these penetrating arteries emerge from the parent artery, they may bifurcate while in the CSF and inside the parenchyma. This arborization pattern may explain the triangular shape observed in some lacunar (eg, penetrating artery) infarcts in coronal views of the basal ganglia or axial views of the brainstem. (Contributed by Dr. Hugo J Aparicio.)