 As we all know that the most important thing when we start our radiology practice and even when we practice later on are the stroke patients and sometimes it can still be confusing even though the anatomy looks simple. So let's begin with this talk on cerebral vascular anatomy. So when we talk of the vascular anatomy all of us know that it has to be arterial and it has to be venous bone. So when we talk of arterial anatomy it is mainly the circle of villus when we are talking of intracranial vessels. So this is a routine top image time of flight reconstructed image when you see whenever you perform your MR angio for the brain. So here you can identify the components of circle of villus. So this one is the middle cerebral artery. Here going ahead on this end on view is the anterior cerebral artery. The internal carotid artery is the artery which is seen better on when you see the coronal sections or the sagittal sections. Here you have the posterior cerebral artery connecting the two completing the circle of villus at the posterior communicating arteries. Similarly anteriorly we will have the anterior communicating arteries here connecting the two anterior cerebral arteries. So in this way there is a complete circulation overlap in the brain so that whenever for some cause if a vessel gets blocked rest of the circulation can take care of it. So we all have seen a lot of cases where the patients have their arteries like even sometimes the posterior circulation is showing thrombus and then we see that the posterior communicating artery becomes very much prominent. So we have seen a lot of times that the entire ICA is showing more flow but there is still flow seen in the MCAs through the posterior communicating arteries. There are various anatomic variations like we can have hypoplastic even segments of the anterior cerebral arteries. So the posterior communicating artery is of a diameter which is bigger than the P1 segment of your posterior cerebral artery. So we will feel that it is as if continuing with the rest of the PCA. So then we call it as a fetal variant of the posterior cerebral artery. Same area when we are going to see in another anterior posterior projection we are going to identify these anterior cerebral arteries. These are the middle cerebral arteries. So from the origin to the first division is the M1 segment of your MCAs. Here is your anterior communicating artery very common site of small or even large aneurysms. So here you have to look for these aneurysms. You may find that there is a patient with lot of subarachnoid hemorrhage along the sides of these arteries and then you can identify on your MR angiosequences based on where the magnitude of the blood is kind of maximum that which area is the most suspicious for having these aneurysms. Sometime because of the subarachnoid hemorrhages the vessels are in spasms. So you may not identify the aneurysm but when you perform your high-resolution MR angiose so even with the 3 tesla scan is now with your top sequences high-resolution MR angiose without contrast can identify aneurysms as small as 3 millimeters in size. But definitely post contrast MR angio or post contrast CT angio will be giving you more sensitive details of these aneurysms. So these are the smaller branches of your basilar artery the posterior circulation which is a part of your circle of will is these smaller branches may not be well identified on your non-contrast top angiose but the vessels which you can identify are your anterior inferior cerebellar arteries and your superior cerebellar arteries posterior cerebellar arteries. ICA which is the posterior inferior cerebellar artery is a branch coming out of the V4 segment of the vertebral artery same circle of will is including the communicating branches. So these images clarify the anatomy very well and these are all our routine images which we see on radiology assistant or radiopedia sites and here we can see that the horizontal part of the MCA from its origin till its division is called as the M1 segment then it takes a small turn and divides into the M2 segment which has usually superior and inferior divisions. These are the cortical branches of your MCAs here you can identify that the lenticulostriate arteries are arising immediately from the ACA A1 segment while the lateral part of it is arising from the MCA. So when you are seeing the infarcts in these areas that is the area of the thalamus basal anglia internal capsules these are the areas supplied by the lenticulostriate arteries immediately by the ACAs and laterally by your MCAs. The most important in the vessel intravenously as we all know is the internal carotid artery and if we revise the parts of these this vessel we know that there are seven segments so C1 is the cervical segment, C2 is the peterous which comes near the peterous apex, C3 is the lecerine segment, C4 is the cavernous segment, C5 that is the tortuous area is the clinoid and the one after that is the supraclinoid. So basically the cavernous segment is relatively easy to identify we know where the site of cavernous sinus is so it is a relatively vertical part of your carotid artery just close to that so that is your cavernous segment afterwards here this tortuous segment is your clinoid and supraclinoid. The segment here that is marked as C3 as we call it the peterous segment so usually the peterous, the lacerum and the cavernous segment is taken together and named as pterocavernous for a general purposes on our reports so most of the times you might get some irregular narrowing related to atherosclerosis in our patients. So another example where they have divided the DSA image of ICA into various segments now this is another important image that we try to refer to in our early residency days and later on kind of remember for our stroke patients so whenever we are describing a case of stroke and in fact we always tend to put a few markers or few tags to our report that is one whether it is hyperacute, acute, subacute or chronic we would like to tell whether it is hemorrhagic or non-hemorrhagic and then we are going to tell them that which vascular territory is involved we will perform MR angios and we will also tell them about if we can see a large vessel or small vessel occlusion and our sworn images we will identify the intravascular luminal thrombus. So here is the same image telling you the distribution so midline parasigital band-like areas are from ACAs, larger part of the brain the one which is marked in yellow is from the MCA territory posteriorly even in the superior part parasigitally is the PCA so sometime this can be a confusing part here is the area of basal ganglia, thalamus and the internal capsule so we will see that with another image in little detail. So same thing in a different manner ACA, PCA and MCA so you have your watershed zones most of the time in patients you might have embolic infarcts if you have some cardio embolic etiology the infarcts will be distributed in different vascular territories that time you can ask your concern physician to correlate with the cardiovascular workup you can have watershed embolic infarcts and also there is some kind of plaque which is unstable in any of these major vessels like MCA or ICAs you can have artery to artery embolic infarcts as well. So here you see the area of basal ganglia the one which is marked in the pink color is the posterior limb of the internal capsule very commonly seen and the patient will have features of dense hemiplegia so this is supplied by your anterior coroidal artery. Inferior sections and when we start with the vermis and the cerebellar hemisphere which we see in details with another image so here is the area of your superior cerebellar artery. This entire midbrain by PCA and basal artery will supply your pons, anterior part which is the hippocampus is anterior coroidal artery and if you have infarcts even smaller infarcts in this area measletemporal and hippocampal region can lead to transient global amnesia so even tiny infarcts of few millimetre size are important. If you see the 3D depiction in another orientation we can again see the distribution of the arterial territories and we can understand that MCA has a bigger contribution to the vascular supply and then you have ACA's and your PCA's posterior. This is image of the posterior forester structure that is your cerebellar hemisphere this is again important and to know that what are the vessels which are supplying your cerebellar so here inferiorly is the posterior inferior cerebellar artery the area which is in grey here is the anterior inferior cerebellar artery and a large part of the cerebellar hemisphere is by the superior cerebellar artery. If you perform a good quality top NGO you can identify smaller thrombus or smaller areas of occlusion and aneurysm even in these small vessels. If you perform a good quality swan images you can identify small van-like areas of looming within which will be suggestive of intra-arterial thrombus. So just a small revision again for this basal ganglia arterial supply anterior coroidal artery in the posterior limb of internal capsule penetrating branches of PCA's in thalamus the ones are yellow in colour are the lateral lenticulostride from MCA and medial lenticulostride from ACA. Just touching upon variants so we know that fetal PCA is something which is commonly seen but there are few more fetal variants which you can have they are persistent branches of fetal origin so here is an example and can be seen in our spotter section of the exam sometimes. So that is the persistent trigeminal artery and similar to persistent trigeminal which you can see here as a communication between the ICA's and the basal artery you can have few other types like the hypoglossal artery, the proatlantic intersegmental artery, otec artery. So these are all communication between your vertebral that is the posterior circulation and your anterior circulation that is your ICA's. So these may be persistently seen and may look odd on your reconstructed angiograms. Sometimes they may be a little partially hypoplastic and then they can mimic aneurysm so it's always suggested that you report your MR angios after seeing the raw data and not only the reconstructed MIPS. Another important variant is your artery of perspiron so that is something which we all know that when you have symmetric areas of infarcts, restricted diffusion involving bilateral thalamai along their medial aspect one of the most possible differential is that you have an artery of perspiron infarct. So this is another variant where both thalamai are supplied by a single vessel that is from one side TCA. So this can be another classification so people kind of classify everything almost so they have classified artery of perspiron but this one is something which is commonly seen a single branch coming out from PCA and then dividing into two. So to summarize there is nothing much to be said but what is important is anatomy is something which require revision and there are lot of variations in the anatomy which may create confusion sometimes so we can always refer to our resources and references and also look at the source images whenever possible for angiograms and we look.