Aneurysm: Definition and Classification, Abdominal Aortic Aneurysm

00:01 So we've talked about how it happens.

00:02 Let's now get more at a gross level.

00:04 So for you future surgeons, you need to understand some of these definitions.

00:09 And also for all of you future clinicians and pathologists, you need to understand these definitions.

00:13 So a true aneurysm of any vessel.

00:16 Here we're talking about an aorta but it could be any vessel.

00:18 A true aneurysm involves all 3 layers.

00:22 So the intima, the media and adventitia are involved and there is dilation.

00:26 And you can have dilation that's minimal.

00:30 We tend to only call something an aneurysm when it exceeds 50% of the normal diameter.

00:36 Okay, before then it's just a slight expansion.

00:44 And because there is laxity in the wall because of the abnormal extracellular matrix production by defective or degenerating smooth muscle cells.

00:53 Each beat of the heart can progressively enlarge this.

00:57 So it enlarges over time.

00:59 And the risk of the complications from an aortic aneurysm increases as the dilation, the aneurysm gets bigger and bigger and bigger.

01:07 We'll see those statistics in a minute.

01:10 You can have a saccular aneurysm with a little outpouching from one side of the vessel wall, so kind of a little, it's like imagine a soft spot in an inner tube.

01:21 And when you inflate it, it kind of pushes out from that soft spot.

01:27 Or you can have diffuse circumferential fusiform aneurysm that's what's indicated on the right.

01:35 A false aneurysm occurs when there is a break and then you have blood that extravasates.

01:42 But it's contained within a fibrous connective tissue capsule of some sort and you can actually wall it off.

01:49 This can formally rupture and then you're going to exsanguinate.

01:52 But if you don't exsanguinate and it's kind of captured by fibrous connective tissue, that's a false aneurysm.

01:58 We don't have all 3 layers in this extravasated area of bleeding.