Thrombus Formation:
  • Can occur due to CHF, extrinsic compression, renal cell carcinoma and other causes  of blood stasis
  • Echogenic material identified in normally anechoic lumen
  • Pulmonary embolism risk is very high
Note: Click any image to enlarge.
Greenfield Filter:
  • Used to prevent emboli from reaching the lungs
  • Surgically inserted into the IVC in patients with a history of DVT in the pelvis and lower extremities
  • Appears as an echogenic "umbrella" in the lumen of the IVC
GREAT VESSEL ANATOMY AND SONOGRAPHIC EVALUATION
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Blood Vessel Anatomy:
  1. Tunica Intima-inner layer endothelial cells, basement membrane is the innermost layer of intimal cells
  2. Tunica Media-middle layer, muscle, thicker and more organized layer in arteries
  3. Tunica Adventitia/Externa-Outer Layer, epithelial cells

***Veins have thinner media layer to allow flexibility of lumen size with varied flow volume***
AORTA


Anatomy:
  • Trunk artery
  • Arises from left ventricle
  • Courses inferior through chest and enters abdomen through the diaphragm
  • Located anterior to the spine and to the left of the IVC
  • More posterior than the IVC until the umbilicus level where it lies more anterior than the IVC
  • Distributes blood to organs and limbs
  • Most cases the branch is named after the organ it is feeding
Paired Branches:
       o        Suprarenal arteries
       o        Renal arteries
       o        Gonadal arteries
       o        Lumbar arteries
       o        Common Iliac arteries
Unpaired Branches:
       o        Celiac Axis - 1st abdominal branch of aorta
       o        SMA
       o        IMA
Anterior Branches:
       o        Celiac Axis        
       o        SMA
       o        IMA
Lateral Branches:
       o        Renal Arteries
       o        Common Iliac arteries


COMMON ILIAC ARTERIES:

  • Bifurcation at L3 vertebra, umbilicus level
  • Supplies legs and pelvis
  • High resistance flow
  • Above the umbilicus, arteries are posterior to veins
  • Below the umbilicus, the arteries are anterior to the veins
  • Evaluated for arterial pathology in longitudinal and transverse planes
Indications to Scan the Aorta:
  • Abdominal pain
  • Pulsatile mass
  • AAA on plain film
  • F/U AAA
  • Trauma

Exam Technique:
  • 2.5MHz to 6.5MHz adult probe
  • 4MHz to 8MHz pediatric probe
  • Patient must be NPO 8-12hrs prior to the exam to best visualize the abdominal vasculature
  • Supine, oblique and decub positions may all be necessary for optimal evaluation
  • Multiple patient positions can help view the aorta behind gas containing bowel loops
  • 2D, Color and Doppler evaluation of proximal mid and distal segments with iliac arteries

Sonographic Appearance:
  • Best anatomic landmark in abdomen
  • Longitudinal-hollow tube anterior to spine
  • Transverse-circular structure
  • Gradual tapering as it courses distally
  • Becomes more anterior in the abdomen as it courses distally

Measurements:
Proximal  2.0-2.6 cm
Mid          1.6-2.4 cm
Distal       1.1-2.0 cm
Iliacs        0.6-1.4 cm


Doppler of the Aorta:
  • High resistance
  • Clean spectral window
  • Biphasic above renals due to low resistance branches to organs
  • Triphasic below renals, supplies lower extremities which cause an increase in resistance
  • Occlusive disease may change resistance and phasicity of waveform
  • Aneurysmal disease may show increased turbulence, especially w/ color Doppler
PATHOLOGY

Abdominal Aortic Aneurysm:
  • Focal dilatation of the aorta >3cm
  • Saccular - formed with a stalk connecting dilated wall portion
  • Fusiform - vessel wall stretches in a circumferential manner; most common type
  • Berry - tiny out pouching, usually found in the cerebrum and splanchnic arteries
  • Above the Renal Arteries - Surgical intervention asap
  • Below the Renal Arteries - Surgical intervention at a diameter >6cm
  • Stent or graft placement usual treatment
Complications:
  • Rupture
  • Decreased flow to extremities
  • Blue Toe Syndrome w/ thrombus accumulation and embolization
  • Affects Renal circulation and systemic blood pressure if suprarenal or juxtarenal in location

Sonographic Appearance:
  • Enlarged vessel >3cm
  • Possible thrombus accumulation causes increased echogenicity in the lumen
  • Measure true vessel size from outer edge of the wall to outer edge of the wall
  • Measure true lumen size if thrombus accumulation present
  • Turbulence seen w/ Color and PW Doppler evaluation
Blue Toe Syndrome:
  • Embolic material lodges in digital arteries in toes leading to cyanosis of the distal tissues
  • Causes: Thrombus in aneurysm, arteritis, ulcerated atherosclerotic lesions, some angio procedures


Dissection:
  • Intimal layer tears and allows flow between the intima and media layers into a blind pocket (false lumen)
  • Remaining lumen (true lumen) is decreased in size due to flap with blood flow beneath it
  • Causes weakened vessel wall, risk of vessel rupture
  • Thrombosis can occur in the false lumen which can cause a significant stenosis/occlusion in the vessel leading to ischemia distal to the dissection
  • Surgical intervention required immediately
Sonographic Appearance:
  • Linear echogenicity seen in the lumen of the vessel, separating it into two channels
  • Color flow demonstrates two lumens, both with turbulence
  • Bidirectional flow seen in false lumen
Pseudoaneurysm:
  • Caused by trauma or invasive procedures
  • Blood escapes the artery into surrounding tissues and is encapsulated within the tissues
  • The connection with the vessel is made through a neck or stalk
  • Thrombin - clotting agent injected into a pseudoaneurysm to close the opening and clot the blood that has escaped
Sonographic Appearance:
  • Rounded, anechoic structure adjacent to main artery
  • Color demonstrates a connection between the artery and the structure
  • Color also demonstrates turbulent flow, Yin/Yang sign within the pseudo
  • Doppler evaluation will demonstrate to-and-fro flow in the stalk and pseudo
INFERIOR VENA CAVA

  • Trunk vein formed by the junction of the two common iliac veins
  • Empties into the right atrium
  • Courses superior through the abdomen to the right of the aorta
  • Posterior to the duodenum and pancreas
  • Posterior and lateral to the portal confluence
  • Returns all of the blood from the legs and some abdominal organs
  • In the abdomen, inspiration increases the diameter
  • In the abdomen, expiration decreases the diameter
  • Valsalva maneuver causes dilatation
  • Abnormal Dilatation >2.5 cm
Tributaries:
  • Common iliac veins
  • Lumbar veins
  • Gonadal veins
  • Renal veins
  • Suprarenal veins
  • Hepatic veins
Indications to Scan IVC:
  • Abdominal pain
  • Palpable mass
  • F/u filter placement
  • Hx renal tumor
  • Thrombosis

Exam Technique:
  • 2.5MHz to 6.5MHz adult probe
  • 4MHz to 8MHz pediatric probe
  • Patient must be NPO 8-12hrs prior to the exam to best visualize the abdominal vasculature
  • 2D, Color and Doppler evaluation of length of vessel

US of the IVC:
  • Longitudinal-tubular structure to the right of the aorta
  • Transverse-oval structure
  • Walls thinner than aorta

Doppler of the IVC:
  • Longitudinal plane
  • Flow toward RA
  • Cardiac pulsatility seen in upper abdominal portion
  • Normal flow described as TRIPHASIC
  • Respiratory changes should be documented
  • Can see respiratory changes in 2D also
IVC Dilatation:
  • Causes include CHF, Pulmonary HTN, Mass Effect, Pregnancy
  • Reduced or no change in diameter with respiration
  • Cardiac pulsatility seen in flow in the extremities due to engorgement of the tributaries and the "ripple effect" of the cardiac contractions
  • > 2.5 cm diameter is abnormal
IVC Tumor Invasion:
  • Occurs with adjacent invasive tumor formation
  • Renal cell carcinoma can invade the renal vein and IVC
  • Liver and cardiac malignancy can also invade the IVC
  • Can lead to thrombus accumulation around the mass
  • Increased risk for pulmonary embolism
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