(a)
(b)
Figure 2: CT angiogram head and neck (continued): note the absence of the left internal carotid artery intracranially and poor opacification of the left ophthalmic artery. There is collateral supply to the left middle cerebral artery from the left posterior cerebral artery (a) and the anterior communicating artery (b). An intact circle of Willis allowed the left middle cerebral artery to maintain supply despite the complete occlusion of the left internal carotid artery.