An injury to the wall of an artery that may result in either subarachnoid hemorrhage, formation of a blister-like pseudoaneurysm, or occlusion of the vessel (Figure 1,2). Partial or complete arterial occlusion may cause a critical decrease in blood flow and in turn oxygen delivery resulting in an ischemic stroke. Dissection may occur spontaneously, be the result of direct blunt trauma or as a complication of angiography. Treatment is either with blood thinning agents i.e. aspirin, plavix or warfarin or with endovascular stenting of the vessel. 

Figure 1
Left: Carotid angiogram demonstrating a dissection with resultant narrowing of the vessel (black arrow) with pseudoaneurysm formation (red arrow).  Right: Image obtained after stenting of injured vessel showing normalization of vessel diameter and diversion of flow from pseudoaneurysm (black arrows)