You are probably familiar with the frontal anatomy of these vessels. The splenic vein passes over the superior mesenteric artery. The renal vessels lie directly below the origin of the superior mesenteric artery. Their distance from the artery is variable, as is the course of the splenic vein (Fig. 3.34a). You may be less familiar with the cross-sectional anatomy of this region. Please note: the renal arteries are posterior and the renal veins are anterior. The left renal vein is physiologically compressed between the aorta and supe- rior mesenteric artery and shows mild congestion on the left side, proximal to the compression site. The right renal artery compresses the vena cava from the posterior side (Fig. 3.34b). The diagram in Fig. 3.34c illustrates these rela- tionships in a lateral oblique view.
Demonstrating the superior mesenteric artery, splenic vein, and renal vessels in transverse section
Vms Ams
Vl
Fig. 3.34 Interrelationship of the superior mesenteric artery, splenic vein, and renal vessels
a Frontal view of the splenic vein (Vl), superior mesenteric artery (Ams), right and left renal artery and vein, and superior mesenteric vein (Vms).
b Cross-sectional view of the vessels in a. There is mild congestion of the left renal vein due to its compression between the aorta and superior mesenteric artery (‹).
c Topography of the superior mesen- teric artery and renal vessels. A = aorta, Tr = celiac trunk, Vc = vena cava. Vms Ams Vl Tr Ams A Vc
cava (Fig. 3.36a). Starting from a plane above the level of the kidneys, slowly move the transducer caudad. If it is not hidden by bowel gas, you can recog- nize the termination of the large right renal vein (Fig. 3.36b). As you slide the transducer lower, the renal vein will appear to “detach” from the vena cava and move laterally toward the kidney. This occurs because the renal vein runs laterally downward at a slightly oblique angle. As the scan moves lower, the vein approaches the renal hilum (Fig. 3.36c). Usually the renal artery, which parallels the vein, will also come into view (Fig. 3.36d, e). An oblique scan parallel to the costal arch can define the full length of the renal vein (Fig. 3.36f). An analogous scanning technique on the left side is very rarely successful in defining the left renal vessels.
Fig. 3.36 Demonstrating the right renal vessels in transverse section
a Transverse scan above the kidney through the vena cava (Vc).
d Now the renal artery, which arises from the aorta (A), comes into view (››).
b Scan at a slightly lower level demon- strates the termination of the renal vein (›).
e The sectioned artery moves closer to the kidney (››).
c Scanning lower, the section of the renal vein approaches the renal hilum (›).
f Oblique scan parallel to the costal arch defines the full length of the renal vein (flflfl).
Demonstrating the renal vessels in longitudinal section
When you view the renal vessels in transverse section, you will see that there are five standard planes for imaging these vessels in longitudinal section (Fig. 3.37). Vrd Vc Ard A Ars Ams Vrs 5 4 3 2 1
Fig. 3.37 The five standard longitudinal sections through the renal vessels
Vrs Ars Ams Vrs A Vrs Ard Vc Ard Vrd Ard 1 2 3 4 5
a Transverse section showing the location of the longitudinal planes. A = aorta,
Vc = vena cava,
Ams = superior mesenteric artery, Ars = left renal artery,
Vrs = left renal vein, Ard = right renal artery, Vrd = right renal vein.
b The five standard longitudinal planes of section.
Plane 1: left renal artery (Ars) and vein (Vrs).
Plane 2: aorta (A), left renal vein, and superior mesenteric artery (Ams).
Plane 3: left renal vein, right renal artery (Ard).
Plane 4: vena cava (Vc), right renal artery.
Plane 5: right renal artery and right renal vein (Vrd).
Place the transducer longitudinally over the aorta and identify the aorta, the superior mesenteric artery, and the compressed left renal vein (Fig. 3.38a, b). Move the transducer to the left in small increments. Observe that the aorta disappears. Now locate the large anterior vein and small artery. You will not be able to track both vessels to the renal hilum (Fig. 3.38c–e).
Fig. 3.38 Demonstrating the left renal vessels in longitudinal sections
c The transducer was moved to the left. The renal artery (›) and renal vein (››) appear immediately to the left of the aorta.
e Scanning farther to the left brings the left kidney (dashed outline) into view.
d The transverse was moved farther to the left, demonstrating the renal artery (›) and renal vein (››) at the hilum. A Ars Vrs A Ams Vl Spleen Kidney a Diagram of the left renal vessels in longitudinal section. Note that the plane of section cuts the aorta (A), the superior mesenteric artery (Ams), the left renal artery (Ars), the left renal vein (Vrs), and the splenic vein (Vl).
b Ultrasound image corresponding to a. Aorta (A), superior mesenteric artery (flfl), left renal vein (›), splenic vein (fl).
Now return to the starting point over the aorta. Scan to the right in small in- crements, and watch the aorta disappear. You can now see the right renal ar- tery between the aorta and vena cava. Just above it are the left renal vein and a longitudinal section of the superior mesenteric vein (Fig. 3.39a). Sliding the transducer farther to the right, you will see the vena cava and the right renal artery crossing behind it (Fig. 3.39b). Keep the artery in view and move the transducer farther to the right. The right renal vein will appear, having emerged from the vena cava (Fig. 3.39c). Track the right renal vein and artery to the renal hilum (Fig. 3.39d). The course of the right renal vessels is shown schematically in Fig. 3.39e.
Fig. 3.39 Demonstrating the right renal vessels in longitudinal section
a Longitudinal scan between the aorta and vena cava. You see the right renal artery (›), left renal vein (flfl), and superior mesenteric vein (Vms).
b The transducer was moved to the right. You see the vena cava (Vc), which crosses over the right renal artery (›).
d Renal artery (›) and renal vein (flfl) at the hilum. Vp Vms Vrd Vc Ard e Diagram corre- sponding to im- age d. Note how the right renal vessels (vein [Vrd] and artery [Ard]) run to and behind the vena cava (Vc), respectively. Vp = portal vein, Vms = supe- rior mesenteric vein. The kid- ney is shown in transparent outline so that you can see the renal artery and vein. c The transducer was moved farther
to the right. You still see the right renal artery, which has split into branches (› and fl), plus the right renal vein (flfl). A gallstone (G) is noted as an incidental finding.