Clinical Cases Vascular Anatomy

Vascular Anatomy on CT Scan

The following will be an overview of cross-sectional cardiovascular anatomy as seen on CT scan. The CT scan below is of cadaver 33492. While looking at the CT images, keep in mind that one good way to distinguish arteries from veins on CT is by the presence of atherosclerotic plaque in many of the large and medium arteries (atherosclerosis is a disease of arteries, not veins, so the presence of radiopacity in a vessel identifies that vessel as an artery).

We will move cephalo-caudally (from the head to the feet) through the CT scan. Start advancing the scan caudally and stop at time 30-35. Notice at locations J12 and L12 that some calcification is seen in both lateral ventricles of the brain. This is calcification of the choroid plexuses (vascular structures responsible for producing CSF via ependymal cells). This calcification is normal and increases with aging. Next look at locations J10 and K10. These are the internal carotid arteries on either side of the optic chiasm (point of cross over of the optic nerves- CN II), just before splitting off into the anterior cerebral, middle cerebral, and posterior communication aa.

Moving into the neck, we can see the common carotids (locations J9.5 and L9.5 at approximately the level of the hyoid bone, time= 40-42) which can be seen just after the mandible disappears and before the thyroid cartilage appears. As we continue moving down continue to follow the carotid aa (and notice how the internal jugular veins run just lateral to them in the carotid sheath). The tracheal lumen can also be followed in the neck anteromedially to the carotid sheath.

As we approach the thorax, continue following the carotid aa and internal jugular vv. Notice at time 45-50 how the clavicle comes over from the shoulders to meet the top of the manubrium. Just beneath the clavicle you will see the left common carotid disappear into the aortic arch (time= 49, location L10) and the right common carotid joins the right subclavian artery (location= J10) to form the brachiocephalic trunk (clinically referred to as the innominate artery).

The venous anatomy at this level is also discernible. Begin again further up the neck where you can see the internal jugular vein. Begin moving down while following the right internal jugular and notice at time 48 how it joins the right subclavian v. just underneath the clavicle to form the right brachiocephalic v (clinically referred to as the right innominate vein). The same can be seen on the left. Now follow the right and left subclavian vv. down to where they join to form the superior vena cava (SVC) at time= 50, J10. The SVC can now be followed down into the right atrium, and if you continue downward, the inferior vena cava (IVC) can be seen emerging from the right atrium (time=60, K10).

Move back up to time= 50, L10 and notice how just posterior to the left brachiocephalic v. is a large structure looping posteriorly. This is the aortic arch, and if followed downward, you will notice how it is seen to split into the descending thoracic aorta posteriorly and the ascending aorta anteriorly. The ascending aorta can be followed down to the aortic root, where it is seen at time= 57, L9 to come from the heart's left ventricle. Just to the left of the ascending aorta at time = 54, L9 the pulmonary trunk can be seen coming out of the right ventricle and branching into the right and left pulmonary arteries. Familiarize yourself with the heart, keeping in mind that the right ventricle lies against the anterior chest well, the left ventricle comprises most of the left lateral border, the left atrium is completely posterior (and can be seen at time= 57, J11 and M11 receiving pulmonary vv.), and the right atrium comprises the right lateral border with the SVC and IVC both feeding into it.

Continue moving down through chest and into the abdomen while following both the descending aorta and the IVC (located time= 60, M12 and K9.5, respectively). See if you can spot the main branches off the abdominal aorta prior to its bifurcation. While watching the abdominal aorta from time 65 to 75, you should see the celiac a, superior mesenteric a (SMA), both renal aa, and the inferior mesenteric a (IMA). Some of these are visible for only a cross section or two, so advance the scan slowly. Now look at the IVC just as it is coming off the right atrium (time= 60, K9.5). Notice how the IVC runs posterior to the liver down into the abdomen. At the level of the SMA, the IVC can be seen giving off renal vv. The left renal v. is seen to cross over the aorta, just underneath the SMA (this relationship is important in kidney transplants- the left kidney is usually harvested from living donors because it affords the surgeon a much longer renal vein to work with when transplanting the organ).

Another point of interest is the porta hepatis. Move back to the level of the liver and look at time= 67, J8. Here you will see the right and left portal veins splitting off from the portal vein. Continue scanning down while following the portal vein and you will see that it is formed by the splenic vein (time= 69, L8) and superior mesenteric vein (SMV- found at time= 71, L8). Notice how the SMV quickly joins the SMA in the abdomen, and how this vessel pair can be seen branching off into their various terminal branches as you continue scanning down.

As we continue following the abdominal aorta and IVC down into the abdomen, we eventually see them split into the common iliac aa and vv (time= 80, J9 and K9). Choose to follow either the right or left pair, and advance the scan down into the pelvis. You should see the common iliacs split into the internal and external iliacs, with the internal iliacs moving posteriorly into the pelvis, and external iliacs moving anteriorly toward the inguinal ligament (at which point they become the femoral aa). Just below the hip joint (location) at approximately the level of the lesser trochanter on the femur, the femoral a gives off the deep femoral artery, which moves deep into the thigh and terminates in lateral and medial circumflex aa, and perforating aa that supply the posterior compartment of the thigh. The femoral artery continues to move down through the adductor canal with the femoral vein. At the level of the knee, the femoral a and v are seen to move behind the knee, with the vein superficial to the artery (time= 120, H12 and O12). At this point these vessels are called the popliteal a and v.