Vascular System Notes

Vascular System: IVC, Portal System, and Aorta

Overview of the Vascular System

  • Composed of the heart and blood vessels.
  • Heart pumps blood; vessels transport it.
  • Veins carry deoxygenated blood from the body to the heart.
  • Blood enters the right atrium, then the right ventricle.
  • From the heart, blood goes to the lungs to release CO_2 and pick up oxygen.
  • Arteries carry oxygenated blood from the heart to the rest of the body.

Veins

  • Carry blood towards the heart.
  • Venous formation starts in the periphery (e.g., limbs, head).
  • Tiny vessels join to form larger vessels.
  • Tributaries drain into larger veins.

Arteries

  • Carry blood away from the heart; they divide and supply blood.
  • Arteries deliver blood to various parts of the body.

Major Veins: IVC and Superior Vena Cava (SVC)

  • Two large veins collect blood from the body: Inferior Vena Cava (IVC) and Superior Vena Cava (SVC).
  • The diaphragm divides the drainage areas.
  • SVC drains venous blood from areas above the diaphragm.
  • IVC drains venous blood from areas below the diaphragm.
  • The diaphragm is a muscle located at the level of the T12 thoracic vertebra, separating the thorax from the abdomen.

IVC Development and Sections

  • The IVC develops from a combination of different parts.
  • Divided into sections:
    • Hepatic
    • Prerenal
    • Renal
    • Postrenal

Hepatic Section

  • Hepatic refers to the liver.
  • Located posterior to the liver.

Renal Segment

  • Contains renal veins.
  • Renal veins arise from the lateral side and run horizontally.
  • Right and left renal veins are important landmarks in scanning.

Intrarenal Segment

  • Composed of lumbar veins from muscles.
  • Right common iliac veins.
  • Gonadal veins (from ovaries or testicles).
  • Gonadal veins run vertically, parallel to the IVC, and drain into it.
  • Left and right side drainage differs, especially concerning the renal vein.

Immediate Tributaries of the IVC

  • Small tributaries may not be visible on ultrasound.
  • Hepatic veins (usually three) enter the IVC before it enters the right atrium.

Suprarenal Veins

  • Right suprarenal vein drains directly into the IVC on the lateral aspect.
  • Left suprarenal vein drains into the left renal vein, not directly into the IVC.

Gonadal Veins

  • Drain blood from the testes and ovaries.
  • Right gonadal vein drains directly into the IVC anteriorly and slightly laterally.
  • Left gonadal vein drains into the left renal vein.

Significance of Drainage Differences

  • Renal tumors can cause thrombus formation, invading the renal vein and causing obstruction.
  • Obstruction can affect drainage from the testes or ovaries, leading to varicosities.
  • Left testicular issues may indicate a need to examine the left renal vein and kidney.
  • Prominent veins and swelling can be indicative of underlying issues.
  • Echogenic flows within veins can be normal but may also indicate clots.

Veins vs. Arteries

  • Veins have valves; arteries (except at the aortic level) do not.
  • Veins drain against gravity, and valves prevent backflow.
  • Malfunctioning valves lead to varicose veins.
  • Veins may show echogenic particles in the lumen (normal).
  • Arterial walls are thicker.

Differentiating Aorta and IVC on Scans

  • Aorta follows the curvature of the spine and has irregular margins related to vertebrae.
  • Aorta is pulsatile.
  • IVC has a more horizontal course and dips towards the right atrium.
  • IVC is anterior to the spine but more to the right side.
  • Hepatic artery and portal vein are anterior to the IVC.
  • Veins are compressible and have variations.
  • Arteries and veins have different spectral flows.

Doppler Blood Flow in Veins

  • Doppler indicates velocity; direction is indicated by whether the flow is above or below the baseline.
  • Venous flow is continuous.
  • Phasic flow changes with respiration.
  • Inspiration increases intra-abdominal pressure, causing a slight dip in the flow.
  • Expiration releases pressure, and flow increases.
  • Absent phasic response indicates obstruction.
  • Phasic flow is seen in the distal IVC below the renal veins.

Pulsatile Flow

  • IVC, hepatic, and subclavian veins (close to the heart) show pulsatile flow reflecting the cardiac cycle.
  • During heart dilation, valves close, and blood flows into the atria.
  • Atrial contraction pushes blood to the right ventricle, causing backward flow.
  • Regurgitation in the atria is normal within limits.
  • Hepatic and subclavian veins show pulsatile flow in the proximal portion of the IVC.
  • Aortic regurgitation can cause multiple upstrokes in venous flow.

IVC Measurements

  • IVC diameter varies with hydration status, exercise, and respiratory cycle.
  • Average diameter should not exceed 3.7 cm.
  • In congestive cardiac failure, the IVC enlarges due to backward blood accumulation.
  • Normal IVC diameter averages around 2.5 cm.

Importance of IVC Identification

  • Easy to locate and helps in finding other structures.
  • Relationship to the vertebral column, aorta, and splenic vein.
  • Left renal vein passes between the aorta and superior mesenteric artery.
  • Relationship to the kidney, splenic vein, tail of the pancreas, and liver.

Ultrasound and IVC

  • Right atrial heart failure affects IVC and portal vein appearance.
  • Visualization of the left hepatic vein, portal vein, and their distribution.
  • Hepatic veins drain blood from the liver.

Hepatic Vein Blood Flow

  • Superior view shows blood flow towards the heart during diastole and atrial contraction.
  • Multiple upward flows indicate tricuspid regurgitation.
  • Hepatic vein waveform gives rise to "hepatofever".
  • Normal hepatic vein blood flow is away from the liver (hepatofugal).
  • The characteristic pattern of hepatic veins is a W-shaped waveform.

Renal Vein

  • Left renal vein runs between the aorta and superior mesenteric artery.
  • Kidney as an important landmark.
  • Normal IVC size: 2.5 to 3 cm.
  • Portal vein size: 1.3 cm.

Thrombus Formation

  • Slow blood flow can lead to thrombus formation.
  • Clots appear as bright echogenic structures within the lumen.
  • Clot obstruction leads to backup flow and swelling.
  • Color Doppler helps visualize patent vs. obstructed lumens.
  • Fresh clots can be difficult to identify.

IVC Embryology and Anomalies

  • IVC develops from parietal and suprarenal parts.
  • Anomalies can occur during embryological development.
  • Double IVC is a rare condition where two IVCs fail to merge.
  • IVC on the left side is another rare anomaly.

Diagnostic Tools

  • Doppler and Duplex ultrasonography are used to detect clots.
  • Vascular surgeons commonly perform DVT (Deep Vein Thrombosis) tests.
  • Venography is less commonly used due to its invasive nature.