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Flashcards in Vascular Deck (21)
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1

What is usually the most accurate way to evaluate the degree of arterial stenosis?

Peak systolic velocity, which is elevated proximal to and at the site of stenosis.

2

DDx of increased peak systolic velocity

  • Downstream (distal) stenosis.
  • Compensatory flow, contralateral to an obstruction or severe stenosis.
  • Physiologic hyperdynamic state in a healthy young patient.

3

DDx of decreased peak systolic velocity

  • Upstream (more proximal) stenosis.
  • Poor cardiac pump function.
  • Near-total occlusion.

4

What are the three components of the carotid artery ultrasound exam?

  1. Evaluation of plaque morphology
  2. hemodynamic evaluation
  3. waveform analysis

5

How is plaque morphology evaluated with ultrasound?

What percent cross-sectional area plaque would not be expected to be hemodynamically significant, and what percent would be? 

  • Plaque morphology is evaluated on grayscale imaging (without doppler) and is described in terms of absolute percent stenosis.
  • <50% cross-sectional area plaque would not be expected to be hemodynamically significant.
  • >50% luminal plaque is expected to show elevation in peak systolic velocity.

6

What is the normal peak systolic velocity in large arteries? 

Give two important examples:

  • Normal PSV in large arteries = 60-100 cm/sec
  • Aortic and renal arteries

7

Per the Society of Radiologists in US (SRU) criteria, at what artery PSV is considered to suggest stenosis?

Potential pitfall?

  • >125cm/sec suggests >50% stenosis.
  • >230cm/sec suggests >70% stenosis.
    • Potential pitfall: An occluded or nearly occluded artery may have no detectable flow.

8

What ratio is a useful secondary sign of ICA stenosis? 

What are the ratios that suggest stenosis?

In what states is this more useful than absolute PSV?

What other velocities can suggest stenosis, and what amount?

  • An elevated ratio of internal carotid artery to common carotid artery (ICA/CCA) PSV is a useful secondary sign of ICA stenosis.
    • <2 is normal.
    • >2 suggests >50% ICA stenosis.
    • >4 suggests >70% ICA stenosis.
  • In high and low flow states, the ICA/CCA ratio is more useful than the absolute PSV
  • End-diastolic velocity of >100 cm/sec suggests >70% stenosis.

     

9

Describe waveform of stenosis downstream (distal) to the transducer (outflow lesion)

Describe waveform of stenosis upstream (proximal) to the transducer (inflow lesion)

What is spectral broadening and aliasing?

 

  • Stenosis downstream (distal) to transducer (outflow lesion): Spectral waveform is high resistance and high velocity in morphology, characterized by decreased diastolic flow. The systolic upstroke is normal and rapid. Spectral broadening and aliasing may be present.
    • Spectral broadening describes the widened distribution of RBC velocities due to disruption of laminar flow.
    • Aliasing is an artifact where the highest velocities are shown to have a reversed flow.
  • Stenosis upstream (proximal) to the transducer (inflow lesion): Spectral waveform is low resistance and low velocity in morphology, with relatively increased diastolic flow. Systolic upstroke is slowed, producing the tardus et parvus waveform.

10

Discuss all the criteria for renal artery stenosis:

  • A peak systolic velocity of >180 cm/sec is consistent with renal artery stenosis.
    • Normal aortic and renal artery velocity is 60-100 cm/sec.
  • A renal artery to aortic velocity ratio of >3.5 is also consistent with renal artery stenosis.
  • Reduced or absent diastolic flow is suggestive of a stenosis distal to the area of interest.
  • As with the carotid artery, a tardus et parvus waveform on spectral doppler is suggestive of a stenosis proximal (upstream) to the transducer, known as an inflow lesion.
  • An elevated renal resistive index (>0.7) is nonspecific but may indicate renal artery stenosis.
    • The resistive index is calculated as follows: RI = (PSV-EDV)/PSV 
    • RI is measured in the segmental arteries of the upper, mid, and lower poles.
    • Elevated resistive indices can also be seen in acute urinary obstruction or medical renal disease.

11

What is the most common cause of renal artery stenosis? 

What part is usually affected?

  • Atherosclerosis is by far the most common cause of renal artery stenosis, typically affecting the ostium of the renal artery.

12

What is fibromuscular dysplasia?

Where is the most common location?

What is the classic angiographic appearance?

  • Fibromuscular dysplasia (FMD) is a vasculitis that primarily affects the renal and carotid arteries in middle-aged females.
  • The most common location of stenosis in FMD is the distal two-thirds of the renal artery.
  • The classic angiographic appearance of FMD is a string of pearls caused by multifocal alternating stenoses and post-stenotic dilations.

13

Discuss the superficial venous LE anatomy

How about the deep venous system? 

  • The great saphenous vein drains into the common femoral vein. Although the great saphenous vein is technically part of the superficial system, clots near the saphenofemoral junction are typically treated with anticoagulation because of their propensity to become dislodged.
  • The small saphenous vein drains into the popliteal vein (which continues proximally as the femoral vein). Clots in the small saphenous vein are typically not treated.
  • The common femoral vein (CVF) drains into the external iliac vein and begins at the level of the inguinal ligament. The CFV lies medial to the common femoral artery.
  • CFV tributaries include the deep femoral and femoral veins.
  • The three calf veins are the anterior tibial vein (lateral), peroneal vein (middle), and posterior tibial vein (medial), which join to form the popliteal vein. 

15

What should a lower extremity venous US exam include?

  • A lower extremity venous ultrasound exam should include venous compression, color and spectral Doppler, and evaluation of venous augmentation and respiratory variation.

16

What is venous augmentation?

What about respiratory respiration?

What do they signify in a DVT study?

  • Augmentation is the normal change in waveform when the calf is compressed. Lack of augmentation suggests a distal venous obstruction between the calf and the transducer.
  • Respiratory variation is the normal change in waveform when the patient inspires. Lack of respiratory variation suggests a proximal venous obstruction.

17

Which veins should be examined in a US DVT study and in what intervals?

  • The popliteal, femoral, proximal deep femoral, and common femoral (including the saphenofemoral junction) veins should be imaged every 2-3 cm with and without compression.

18

What is the hallmark sonographic finding of a DVT?

  • The hallmark sonographic finding of a DVT is a noncompressible vein with or without an intraluminal clot. A partially thrombosed vein may be partially compressible, while a completely thrombosed vein will not be compressible at all.

19

AAA

Screening?

Parameters for elective tx?

  • Ultrasound is a principal screening modality for abdominal aortic aneurysm, with a proven mortality benefit in 65-79-year-old men who have ever smoked tobacco.
  • If an aneurysm is present, the diameter is measured in three orthogonal planes.
  • Aneurysms with an axial diameter of >5.5 cm should be considered for elective treatment.
  • Aneurysms 3-5.5 cm are typically followed.

20

What is the utility of color Doppler in a DVT US study?

  • Color Doppler is almost always used to help localize the veins, but it is not necessary for diagnosing DVT.
  • Normal color Doppler flow in a noncompressible vein is suspicious for nonobstructing thrombus.

22

How do you differentiate an acute vs chronic DVT?

  • While the diagnosis of DVT is usually straightforward, distinguishing between acute and chronic thrombus can be difficult. Evaluation of the clot’s echogenicity is not a reliable way to determine the acuity of the clot as artifactual echoes within the vein lumen can overlap with the clot.
  • Sonographic findings of chronic venous thrombus include clot retraction and poor visualization of the clot, only partial compressibility, irregularly echogenic and thickened vein walls, and prominent collateral veins.

23

What is an aortic dissection?

The characteristic intimal dissection flap in an aortic dissection is typically hypo- or hyperechoic?

  • In aortic dissection, a tear in the intima allows blood into the media. The characteristic intimal dissection flap is typically echogenic.
  • Color Doppler may show flow in both true and false lumens, often with different flow rates.