Great Vessels of the Abdomen

General Concepts

Arterial Blood Supply

• Arteries move blood away from the heart.

• Typically transport oxygenated blood; exception: pulmonary arteries.

• Arteries are designed to maintain blood flow and blood pressure.

• Vessel walls have 3 layers: tunica intima, tunica media, adventitia.

Venous Blood Supply

• Veins return blood to the heart.

• Typically carry deoxygenated blood; exception: pulmonary veins.

• Lower pressure, walls are collapsible.

• Larger veins are formed by the union of smaller veins.

The Abdominal Aorta

Overview and Location

• Starts at the aortic hiatus of the diaphragm: T12.

• Travels along the anterior curvature of the spine.

• Proximal portion sits more posteriorly; distal portion sits more anteriorly.

• Located slightly left of midline.

• Runs parallel to, and on the left side of, the IVC.

• Bifurcates at the level of L4 (abdominal aorta bifurcation).

• Retroperitoneal.

Major Proximal-to-Distal Branches

1. Celiac Trunk (Axis)

   • First major branch of the aorta below the diaphragm.

   • Approximately 1 ext{ cm} in length.

   • Located on the anterior aspect of the aorta.

   • Divides into 3 branches:

     • Common hepatic artery: travels toward the liver; divides into hepatic artery proper and gastroduodenal artery.

     • Splenic artery: travels left along the superior aspect of the pancreas; supplies spleen and pancreatic tail.

     • Left gastric artery: travels left along the lesser curvature of the stomach; supplies stomach.

2. Adrenal Arteries (Suprarenal Arteries)

   • Paired arteries.

   • Arise from the lateral aspect of the aorta.

   • Originate between the level of the celiac axis and the SMA.

   • Course obliquely (lateral and superior) to the adrenal glands.

   • Not typically identified with ultrasound.

3. Superior Mesenteric Artery (SMA)

   • Second anterior branch of the abdominal aorta.

   • Courses anteriorly and then hooks inferiorly.

   • Supplies the small intestine, ascending colon, and right and mid transverse colon.

4. Renal Arteries

   • Paired arteries; lateral branches of the aorta.

   • Branch just inferior to the level of the SMA.

   • Right renal artery (RRA) passes posterior to the IVC and is longer than the left renal artery (LRA).

   • The renal arteries run posteriorly to the renal veins.

   • The RRA sits slightly inferior to the LRA.

5. Gonadal Arteries

   • Paired arteries; originate from the anterior aorta.

   • Branch off the aorta inferior to the renal arteries.

   • Travel inferiorly and obliquely.

   • Also known as ovarian (female) or testicular (male) arteries.

6. Inferior Mesenteric Artery (IMA)

   • Anterior branch off the aorta at about L3.

   • Takes an inferior and leftward path.

   • Supplies: left transverse colon, descending colon, sigmoid colon, and rectum.

   • Not typically seen on ultrasound; to visualize related structures, view in transverse plane since the liver occupies much space on the right.

7. Lumbar Arteries

   • Paired arteries (4–5 sets).

   • Arise lateral and posterior from the aorta.

   • Supply the lumbar region.

   • Not typically seen on ultrasound.

8. Median Sacral Artery

   • Most inferior branch of the aorta.

   • Supplies the sacrum.

   • Not seen on ultrasound.

9. Common Iliac Arteries (CIA)

   • Aorta bifurcates at L4 to form right and left CIA.

   • Arteries travel downward and laterally.

   • The common iliac arteries sit anterior to the common iliac veins.

   • Branch into internal and external iliac arteries.

   • Note: “varies per person” (anatomic variation).

Venous Blood Supply – Inferior Vena Cava (IVC)

IVC Basics

• Largest vein in the body.

• Returns blood to the right side of the heart.

• Formed by the union of the common iliac veins at L5.

• Pierces the diaphragm to enter the thorax at T8.

• Superiorly, the IVC sits more anterior than the aorta; inferiorly, it sits more posterior than the aorta.

• The IVC is retroperitoneal along its course in the abdomen.

Tributaries of the IVC

1. Common Iliac Veins

   • Formed by the union of the external and internal iliac veins.

   • Travel obliquely from lateral to medial.

   • Sit posterior to the common iliac arteries and posterior to the ureters.

   • Union forms the IVC.

2. Lumbar Veins (veins entering the IVC)

   • 4–5 pairs.

   • Enter the lateral walls of the IVC.

   • Accompany the lumbar arteries.

3. Gonadal Veins

   • Also called testicular (males) or ovarian (females) veins.

   • Paired and ascend along the psoas muscles.

   • Run anterior to the ureters.

   • Right gonadal vein drains into the anterior IVC below the renal vein.

   • Left gonadal vein drains into the left renal vein (not directly into the IVC).

4. Renal and Adrenal Venous Relationships

   • Renal veins:

     • Exit the renal hilum and drain into the lateral IVC.

     • Renal veins lie anterior to the renal arteries.

     • Right renal vein is shorter than the left.

     • Left renal vein crosses posterior to the SMA and anterior to the aorta (known as the “nutcracker” relationship with SMA).

   • Adrenal (suprarenal) veins:

     • Travel along the same path as the arteries.

     • Right adrenal vein drains into the IVC.

     • Left adrenal vein drains into the left renal vein.

     • Small and not typically identified on ultrasound.

5. Hepatic Venous System

   • Hepatic veins:

     • Right, middle, and left hepatic veins.

     • Drain distinct regions of the liver.

     • Travel from an anterior-inferior position within the liver to a posterior-superior position to join the IVC.

     • Empty into the IVC just inferior to the diaphragm.

     • Considered one of the two venous systems in the liver along with the portal venous system.

Practical Imaging Notes and Exam Takeaways

• For ultrasound visibility, some arteries/veins (e.g., adrenal arteries, median sacral artery) may not be visualized directly.

• Cross-sectional orientation matters for visualizing certain vessels (e.g., IMA may be hard to see; left-sided vessels may be better seen in transverse views to account for liver and gastric gas in the right upper quadrant).

• Relationships such as SMA crossing over the left renal vein and its relation to the aorta are critical to identify on cross-sectional imaging.

• Distinguish arteries vs. veins by flow direction and wall characteristics on ultrasound (arteries thicker, more muscular; veins more collapsible, thinner walls).

• Remember the left-right vessel relationships: left renal vein crosses SMA and goes anterior to the aorta; right renal vein lies closer to the IVC and is typically shorter.

• Visualize the IVC in sagittal and transverse planes to appreciate its tributaries and its anterior-posterior relation to the aorta at different levels.

• Recognize that some vessels are not routinely seen sonographically (e.g., median sacral artery, adrenal arteries) but understanding their origin and course helps in cross-sectional anatomy comprehension.

Quick Reference Recap (Key Numerical Anchors)

• Aortic bifurcation: L4

• IVC diaphragmatic entry: T8

• Origin of IMA: around L3

• Gonadal arteries arise inferior to renal arteries from the aorta.

• Renal arteries typically arise just inferior to the SMA.

• Common iliac vein formation and anatomy around the bifurcation region are essential for understanding venous drainage to the IVC.