hello everybody and welcome back to another anatomy tutorial today i'm going to show you how to identify the different liver segments on a ct scan we're going to first look at this diagram to understand how we separate the liver into the various segments and then we're going to go to axial ct slices and i'm going to show you which structures you need to identify in order to figure out which segment of the liver you're actually looking at so let's have a look at this diagram we're looking at the patient front on the patient's left is on this side and the right is on this side here and posterior to the liver we can see our ivc running upwards and in the superior aspect it's receiving blood from three different tributaries our left hepatic vein our middle hepatic vein and our right hepatic vein and you can see from the diagram that these veins separate the liver into four different sections we've got our left lateral section left medial section right medial section and our right lateral section here now on the right hand side our liver actually runs posteriorly around the back here so sometimes this is called the right anterior section and the right posterior section that's interchangeable medial lateral or anterior posterior you can see that we separate then these sections into segments a superior and inferior segment and this separation is not on the diagram here but we'll have our portal vein coming into the liver giving us our right portal vein and our left portal vein and it's those portal veins that separate the superior and the inferior segments from one another and i'm going to show you how to identify that on a ct scan then in terms of numbering we go in this clockwise fashion here if we were looking straight at the patient so we'll start with two on our left superior lateral section work our way three four is the one is the odd one out where we've got a four a and a four b it's easy to remember four a's above for b is below so four is this whole segment but it's separated into two different uh segments for a and four b then we go five head round posteriorly and inferiorly six we go superiorly still posterior seven and then into eight and you may notice that one is here with its own little vein coming in there this is what's known as the chordate lobe and it's got its own different segment and it's very easy to identify it on a ct scan separate from the rest of these lobes and that is going to be segment one here it acts as its own functional unit so back in the day we used to separate the lobes based on their morphology but now we prefer to separate them into these segments because each segment here acts as its own functional independent unit so segment eight would be able to survive on its own independent of the other segments because it's got its own blood supply its own venus and bilious and lymphatic drainage and that helps clinically if we were to then remove a segment or leave a segment behind we would know that that segment would function independently of all the other segments so let's move on to our ct scans we're going to be looking at a portal venous phase ct scan of the abdomen here these are axial slices and i'm just scrolling up superiorly through the liver here we want to see that the liver is in fact on the right hand side of the patient want to scroll through looking at the liver parenchyma scrolling all the way through can we see any masses is there anything abnormal looking going all the way down to the bottom and then we can scroll up to the top now the first thing that we need to identify is our inferior vena cava below so that we can find our hepatic veins coming into the inferior vena cava and we know that ivc is a right-sided structure it lies posterior to the liver so we can suspect the vessel the large vessel that lies posterior to the liver on the right hand side is in fact our ivc and one good way of checking here is we can see our renal veins coming into the ivc itself if you watch the abdominal aorta video i'll link it above we know that our left renal vein runs anterior to our aorta and posterior to our sma there so we can see our left renal vein our right renal vein coming into our ivc and as we scroll upwards we'll see that left middle and right hepatic veins you can see them here coming into the ivc there now we're going to use those hepatic veins our left hepatic vein we're going to draw a line like this middle hepatic vein draw a line like that and right hepatic vein draw a line out to the periphery like that we're going to use that to separate it into our four different sections then we need to identify our portal vein to see where we're going to split those sections into a superior and inferior segment so our portal vein lies anterior to our ivc it gets blood from our splenic vein here as well as our smv it's our superior mesenteric vein that comes to form our portal vein portal vein comes into the porter hepatis here and divides into our left portal vein and our right portal vein so our right portal vein is slightly inferior to this left portal vein and we use that as our horizontal level to separate our superior and our inferior segments from one another so let's start at segment one and work our way all the way to segment eight we're going to start at the top of the lever here so we can see where we are separating our lobes and as you'll notice just medial to our ivc there's this functional unit here separate lobe called our chordate lobe we can scroll all the way through that chordate lobe we can see a vessel coming into that chordate lobe of the vein draining into the ivc here and the coordinate lobe is actually really clinically important so it's important to look at the chordate lobe on every scan you go through look at its size especially sometimes they can become much bigger in cirrhosis and our right over the liver as that gets smaller our chordate lobe gets bigger and the ratio between those changes and we can use that as a marker for cirrhosis that is segment one we look all the way through let's find segment two we know that's superior and we know it's in the left lateral section so we separate again here our left hepatic vein we know that lateral to that is our segment two so we follow all of this is segment two all the way down until we get to the level of the left hepatic vein here so above that is all segment two here as we get to the level of our left hepatic vein we know that inferior to segment two we were labeling down the clockwise position below that is going to be segment three so let's see then segment three all the way down here we can see our falsiform ligament coming through here some people use that as a marker between segment three and segment four but technically we should be using that hepatic vein so sometimes that falsiform ligament is varied amongst people often surgically will use that as a point to take out that lobe of the liver but technically we need to use that left hepatic vein in order to delineate segment three from segment four then let's head back up to the top of the lever again we know that we have four a and four b on that left medial segment of the liver so in between our left hepatic vein and our middle hepatic vein all of this here is segment 4a 4a all the way down and still 4a until we get to the level of our left portal vane below that now is going to be 4b all the way down all of this section here is segment 4b so if we were to see a lesion here we could write confidently in our report this is segment 4b and the person reading that report will understand where we're talking about then we need to find segment 5. now we know that segment 5 is on the right anterior section and it's an inferior segment as we come around we go five six seven and eight back up so let's find our divisions again here's our middle hepatic vein and here's our right hepatic vein we know that if we scroll down here until we see our right portal vein a right portal vein we know that inferior to that here is our segment five all of this here is segment five and as we scroll up until we get to the level of our right portal vein that is all segment five and then we know posterior to that or around the corner laterally in posterior is segment six as we go around labeling it so if we go back up to the top find our right hepatic vein this here we follow this segment down all the way until we can see our right portal vein we know that inferior to our right portal vein all of this is segment six coming down sometimes the segment can really dive down that's called reedle's lobe and that's a normal anatomical variant don't confuse that for hepatic hypertrophy so we've got there we go here at the back here posteriorly we've got segment six and as we head up superiorly get to the level of the right portal vein we know that above that this segment here is all segment sevens posterior to this right hepatic vein and and superior to that right portal vein is our segment seven all the way down until there till that level and as we go up here up here this is all segment seven and that leaves us with our last segment the segment anterior to segment seven we can see our middle hepatic vein our right hepatic vein and we're superior here we're at the top level you can see we're actually into the thorax here our lung fields we can see that this segment all the way here this segment you can see why it's sometimes called the right anterior segment or the right medial segment as we follow that down this is all segment eight until we get to this level the level of the right portal vein and as i've done with various other talks in the past i'm going to link this radiopaedia playlist below and as you can see at the end of this playlist there's a beautiful color-coded diagram here showing you the various segments of the liver and as i've said before learning anatomy is all about repetition going through multiple scans seeing the subtle variations and identifying the structures for yourself that's how you'll start remembering these things over and over again there's no use in remembering strange mnemonics that you're just going to forget repetition repetition repetition will allow you to confidently identify the different anatomy so i hope that's helped let me know what other anatomy videos you would like me to cover in the future and until next time i'll see you all in the next video goodbye