Abdominal Vascular Anatomy

Abdominal Vasculature

• Blood vessels have 3 layers:
  • Tunica adventitia: outermost layer, encapsulates the blood vessel in a thin fibrous wall, contains vasa vasorum (tiny veins and arteries) and nerves
  • Tunica media: middle layer, composed of smooth muscle and external elastic membrane
  • Tunica intima: innermost layer, composed of endothelium, basement membrane, lamina propria, and internal elastic membrane

Abdominal Aorta

• Located in the retroperitoneal cavity, anterior and left of the IVC and spine
• Originates from the left ventricle of the heart
• Posterior to the diaphragm, which divides the aorta into the descending thoracic and abdominal aorta
• Bifurcates into the right and left iliac arteries at the umbilicus
• Normally ≤ 3 cm in diameter, tapering to a narrower diameter as it descends

Branches of the Abdominal Aorta

• Celiac trunk: the 1st branch of the abdominal aorta, originates from the anterior aorta 1-3 cm below the diaphragm
  • Separates the proximal and distal abdominal aorta
  • 3 branches:
    • Common hepatic artery (CHA)
    • Splenic artery (SA)
    • Left gastric artery
• Superior mesenteric artery: the 2nd branch of the abdominal aorta, originates from the anterior aorta 1-2 cm below the celiac trunk
  • Runs parallel to the anterior aorta and posterior to the pancreas
  • Normally 6 mm in diameter
• Right and left renal arteries: branches of the abdominal aorta that supply the kidneys
  • Originate from the lateral walls of the aorta
  • Right renal artery is longer than the left due to proximity to the right kidney
• Gonadal arteries: branches of the abdominal aorta that supply the reproductive organs
  • Difficult to visualize with ultrasound due to small size
• Inferior mesenteric artery: the last branch of the abdominal aorta before it bifurcates into the right and left iliac arteries
  • Originates from the anterior lateral side of the aorta, 4 cm away from the bifurcation
  • Limited visualization on ultrasound due to small size

Abdominal Veins

• Inferior vena cava (IVC):
  • Located in the retroperitoneal cavity, anterior to the spine, posterior to the intestines and the caudate lobe of the liver, and to the right of the aorta
  • Passes through the diaphragm and terminates in the right atrium of the heart
  • Formed by the convergence of the common iliac veins
• Hepatic veins: the 1st branches of the IVC
  • Located just superior to the renal veins
  • Hepatofugal flow: blood moves away from the liver
  • 3 branches:
    • Right branch
    • Middle/intermediate branch
    • Left branch
  • Normally 4-7 mm in diameter
  • Pulsatile Doppler waveforms
• Renal veins:
  • Located just inferior to the renal arteries
  • The LRV is longer than the RRV due to proximity
  • No pulsatility in Doppler waveforms
  • Objective: drain deoxygenated blood from the kidneys back into the IVC
• Superior mesenteric vein (SMV) and splenic vein (SV):
  • Join to form the portal vein
  • Drain the proximal portion of the large intestine and portions of the small intestine

Portal Venous System

• Portal veins have hyperechoic borders on a 2D image
• Main portal vein (MPV or PV):
  • Originates from the junction of the SMV and SV, posterior to the pancreas and just to the right of the midline
  • Bifurcates at the porta hepatis into right and left portal veins
  • Normally < 13 mm in diameter
• Right portal vein (RPV):
  • Runs centrally and horizontally in the right lobe of the liver
  • Bifurcates into anterior and posterior branches that divide the right lobe of the liver into anterior and posterior segments
• Left portal vein (LPV):
  • Runs in the left lobe of the liver
  • Branches divide the left lobe of the liver into medial and lateral segments