Cerebral Vessels Anatomy of the Cerebral Circulation Blood flow entering the brain is supplied by two pair of arteries:the left and right internal carotid supply the anterior circulation; the left and right vertebral arteries. These two arteries merge to form the basilar artery at the base of the skull and supply the posterior circulation. ICA Internal Carotid A & branches (the ICA bifurcates into the ACA & MCA) ACA -  Anterior cerebral artery A-Com - Anterior communicating Artery MCA - Middle cerebral artery P-Com - Posterior communicating artery VA Vertebral artery (the left and right vertebral arteries join to form the basilar artery) Basilar artery & its branches PCA - Posterior cerebral artery SCA - Superior cerebellar artery PICA - Posterior inferior cerebellar artery Together the anterior communicating, anterior cerebral, internal carotid, posterior communicating and posterior cerebral arteries form the vascular network, known as the Circle of Willis. The left and right sides of the circulation are mirror images of each other. If one of the vessels is occluded or temporarily clipped, there may be distal collateral flow via the communicating arteries.   Terminology Balloon Occlusion Test - occluding a cerebral artery with a balloon tipped catheter to determine if the brain can function adequately without flow from this vessel. Burst Suppression - the use of brain protective agents, such as etomidate, to decrease the metabolic demands of the tissue. Cerebral Angiogram - a procedure in which a contrast medium or dye is injected into the brain to visualize the cerebral circulation. Angiograms are always performed prior to aneurysm surgery to determine the exact location of the aneurysm. Cerebrospinal fluid - the clear fluid that surrounds the brain and spinal cord. Coiling an Aneurysm - a non-surgical treatment for aneurysms that uses a catheter to introduce tiny metal coils into the aneurysmal sac sealing it off from the main circulation. Moyamoya Disease - a rare, chronic occlusive cerebrovascular disease in which there is progressive stenosis of the Circle of Willis. Parent vessel - the main artery from which the aneurysm or a tumor arises. Permanent Clip - used to clip off the aneurysm from the main circulation. The clips come in many sizes and configurations. Sometimes more than one clip is needed to completely isolate the aneurysm. These clips are permanently implanted in the patient. Residual Aneurysm - an aneurysm that is not completely clipped and still has some flow circulating through it. Temporary Clip - these clips are placed temporarily on the vessel proximal or distal to the aneurysm as a precautionary measure. Temporary clipping prevents catastrophic hemorrhaging if the aneurysm ruptures during the clipping procedure.