Duplex Imaging of the Lower Extremity Venous System Flashcards

Duplex Imaging of the Lower Extremity Venous System

Background

• Duplex ultrasound is the preferred method for imaging Deep Vein Thrombosis (DVT).
• It's used to:
  • Diagnose DVT.
  • Localize the thrombus.
  • Determine the age of the thrombus.
• It can also reveal incidental vascular and nonvascular findings.
• The process is highly sonographer-dependent, requiring proper training and adherence to standardized protocols.

Anatomy: Deep Veins

• Deep veins are the main pathways for blood returning to the heart.
• They typically accompany an artery of the same name.
• Located beneath the muscular fascia.
• Thrombus in the deep system:
  • Presents a higher risk for embolism due to the squeezing action of surrounding muscles.
  • Is usually larger than in the superficial system.
  • Is more likely to lead to a life-threatening pulmonary embolism (PE).

Anatomy: Specific Deep Veins

• Inferior Vena Cava (IVC)
• Iliac veins
• Common femoral vein
• Femoral vein
• Profunda femoris vein (deep femoral vein)
• Popliteal vein
• Tibio-peroneal trunk
• Posterior tibial veins
• Peroneal veins
• Anterior tibial veins
• Dorsalis pedis veins
• Muscular veins of calf (considered deep):
  • Gastrocnemius veins
  • Soleal sinus veins (storage vein)

Anatomy: Superficial Veins

• Superficial veins travel close to the skin surface in the subcutaneous tissue (located between the skin and the muscular fascia).
• They are smaller than deeper veins.
• Play a significant role in regulating body temperature.
• Thrombus in superficial veins:
  • Is less likely to cause life-threatening PE as the thrombus is smaller and the veins are not surrounded by muscles.
  • Has a greater potential for embolus if the thrombus is near the junction with the deep system.
• Thrombus in superficial veins is called superficial thrombophlebitis.

Anatomy: Specific Superficial Veins

• Great saphenous vein
• Small saphenous vein
• Anterior accessory great saphenous vein
• Posterior accessory great saphenous vein
• Cranial extension of small saphenous vein (vein of Giacomini)
  • The vein of Giacomini can terminate directly into the femoral vein or inferior gluteal vein, or communicate with the GSV.

Anatomy: Perforators

• Perforators connect superficial veins to deep veins.
• Their role is to prevent blood from spending too much time near the skin surface.
• They have one-way valves to keep blood moving toward the deep system.
• If not functioning properly, blood can pool in distal legs, causing stasis changes and venous ulceration.

Venous Valves

• Unique to the venous system.
• Folds of the intima are bicuspid.
• Valves maintain unidirectional flow (superficial to deep), offsetting the effects of hydrostatic pressure.
• Veins that do not contain valves are the IVC, SVC, innominate, iliac veins, and soleal sinuses.
• External iliac has valves in 25% of the population.

Risk Factors: Virchow's Triad

1. Changes or injury to vein walls
2. Venous stasis
3. Hypercoaguability of blood

Pathophysiology

• Vessel wall injury
  • Affects the body’s normal thrombolytic system
  • Can result from catheter injury or trauma
• Venous stasis
  • Allows for increased exposure to clotting factors.
• Hypercoagulability
  • Associated with various diseases (e.g., cancer) or medications such as birth control pills or hormone replacement therapy.
  • Genetic factors also play a role.

Risk Factors: Venous Stasis

• Bed rest
• Immobility
• Myocardial infarction
• Congestive Heart Failure (CHF)
• Chronic Obstructive Pulmonary Disease (COPD)
• Obesity
• Pregnancy
• Estrogen intake
• Previous episodes of DVT
• Paraplegia

Risk Factors: Hypercoagulability of Blood

• Pregnancy
• Cancer
• Estrogen intake
• Myeloproliferative disorders

Risk Factors: Changes/Injury to Vein Walls

• Trauma
• Surgery
• Iatrogenic injury

Pathophysiology: Thrombus Formation

• Venous thrombi commonly begin around valve cusps in the calf.
• These are areas of slower blood flow where stagnation leads to coagulation.

Signs & Symptoms

• Many patients are asymptomatic.
• When symptoms are present, they include:
  • Extremity pain and tenderness
  • Swelling
  • Warmth of extremity
  • Redness of extremity
  • Venous distention
  • Discoloration (brawny discoloration in the gaiter zone – associated with chronic DVT).
  • Palpable cord (associated with superficial thrombophlebitis).

Signs & Symptoms: Pulmonary Embolism (PE)

• A blockage of an artery in the lungs by a substance (e.g., blood clot) that has moved from elsewhere in the body through the bloodstream.
• Can be life-threatening and requires prompt treatment.
• Symptoms related to PE include:
  • Tachypnea
  • Chest pain
  • Tachycardia
  • Shortness of breath
• Clinical markers that can aid in diagnosis include:
  • Well’s criteria
  • D-dimer
  • Both have poor sensitivity and specificity.

Well's Criteria for DVT Probability

• +1 Point Each For:
  • Active malignancy
  • Paralysis, paresis, or recent plaster immobilization of lower limb
  • Recently bedridden for more than 3 days or major surgery/trauma in past 4 weeks
  • Localized tenderness along distribution of lower extremity deep veins
  • Entire lower limb swollen
  • Calf swelling more than 3 cm compared with asymptomatic leg
  • Pitting edema on symptomatic leg
  • Collateral superficial veins on symptomatic leg
• -2 Points For:
  • Alternative diagnosis as likely or more likely than that of DVT
• Probability for DVT:
  • High: >= 3 points
  • Intermediate: 1-2 points
  • Low: 0 points

Patient Positioning

• Bed should be tilted in reversed Trendelenburg position to allow veins to fill with blood, making them easier to visualize.
• Legs can dangle off the edge of the bed to visualize calf veins (may require increased transducer pressure to compress).
• Patient should lie flat on their back (supine) with knee slightly bent and hip slightly externally rotated.

Anatomical Imaging: Common Femoral

• Transverse view at the level of the groin.
• The common femoral artery (CFA) and vein (CFV) are visualized side by side.

Anatomical Imaging: Common Femoral and Great Saphenous Veins

• Transverse view of the bifurcation of the common femoral artery into the SFA and deep (profunda) femoral artery (PFA), while the GSV terminates into the CFV.
• Longitudinal view of the GSV terminating into the CFV just below the level of the inguinal ligament.

Anatomical Imaging: Femoral Vein and Deep Femoral Vein

• Transverse view of the FV and DFV in the upper thigh.
• Also shown is the SFA and the deep femoral artery (DFA).
• Color can be added to assist in vessel identification.

Anatomical Imaging: Popliteal Vein

• A split screen view of the popliteal artery (A) and vein (V).
• The popliteal vein should be fully open and completely compressed with pressure.

Anatomical Imaging: Gastrocnemius Veins

• Transverse view of the gastrocnemius artery (A) and veins (V) in the upper calf.
• Also in view is the popliteal artery (PA) and the popliteal vein (PV) deep to the gastrocnemius vessels.
• The small saphenous vein (SSV) is superficial to the gastrocnemius vessels.

Anatomical Imaging: Small Saphenous Vein

• Longitudinal view of the SSV terminating into the popliteal vein.

Anatomical Imaging: Posterior Tibial and Peroneal Veins

• Transverse view of the medial calf with the posterior tibial veins (PTV) and peroneal veins (Pero V).
• The large anechoic area below the peroneal veins is the fibula.
• Color can be added; companion arteries are also shown (A).

Anatomy: Tibial Veins

• Paired deep calf veins below the level of the popliteal vein:
  • Posterior tibial veins
  • Peroneal veins
  • Anterior tibial veins
  • Dorsalis pedis veins
  • Gastrocnemius veins
  • Soleal sinus veins
• Main deep veins of the calf:
  • Posterior tibial veins (PTV)
  • Peroneal veins (Per V)
  • Anterior tibial veins (ATV).

Anatomy: Soleal Sinus Veins

• Major storage for blood in the calf.
• Common site of thrombus formation.
• Blood only moves out when calf muscles contract.
• Prone to thrombus formation due to stagnation (e.g., following surgery, long plane trip).
• Communicate with PTV and peroneal veins.
• Thrombus can easily extend into major deep veins.

Anatomy: Iliac Veins

• Usually not evaluated in an LEA study unless clinical indications suggest involvement.
• Doppler signal at CFV provides indirect assessment:
  • Phasic flow at CFV suggests lack of obstruction.
  • Continuous flow suggests IVC or iliac obstruction.
• Imaging in pelvis and abdomen complicated by the depth of vessels, overlying bowel gas, and the inability to compress vessels.
• Must rely on color and spectral Doppler LEV

Iliac Veins: Waveforms

• Compare Bilateral CFV Waveforms
  • Normal ipsilateral flow with respiratory variation
  • Steady, continuous flow suggests proximal DVT or extrinsic compression

Technical Considerations & Pitfalls

• Compressions are essential; however, caution should be used in the presence of venous thrombosis (especially with nonocclusive, free-flowing tail).
• Limited visualization of veins due to body habitus.
• Optimize equipment settings for a deeper field of view.
• Difficult compression of deeper veins (e.g., FV through adductor canal):
  • Use the free hand to press from the posterior aspect of the thigh against the transducer.
  • Lateral and posterior approaches may be useful.

Diagnosis: Normal Findings

• Thrombus-free veins will compress completely with transducer compressions (walls must completely coapt).
• Valve sinuses may appear as slight dilations of the vein.
• Valve leaflets may be seen as thin white structures within the sinus and should move freely.
• The most significant diagnostic criteria during venous imaging is how the veins respond to transducer pressure.

Diagnosis: Normal Doppler Signals

• Spontaneous Doppler signals
• Respiratory phasicity
• Augmentation with distal compression
• Cessation of flow with proximal compression or Valsalva maneuver
• Flow should be unidirectional toward the heart
• Angle correction is not needed because PSV does not provide any clinical information

Diagnosis: Abnormal Findings - Determining the Presence of Thrombus

• Echogenic material is visualized within the vein lumen, and this material prevents complete compression of vein walls.
• Increased transducer compression to deform the artery can help determine the presence of thrombus in cases where intraluminal echoes are difficult to visualize.
• Duplex imaging can not only determine the presence of thrombus but also the age of the thrombus, which determines treatment options.

Diagnosis: Acute DVT

• May be sonolucent.
• Spongy.
• Loosely attached (tail of the dog).
• Dilated vessel lumen.
• No collaterals.

Diagnostic Criteria for DVT

Diagnosis: Chronic Thrombus

• Chronically thrombosed veins may be difficult to differentiate from surrounding tissue.
• May not totally obstruct the vein; blood may flow through the residual lumen (recanalization).
• May appear as a thin scar within the vein.

Diagnosis: Abnormal Color and Spectral Doppler

• In a thrombosed vein:
  • Absence of color flow and spectral waveforms.
  • No augmentation with distal compression (indicating obstruction between the level of the transducer and the site of distal compression).
  • Continuous flow indicates a more proximal obstruction (pressure in the vein exceeds pressure changes within the abdomen during respiration).

Diagnosis: Abnormal Pulsatile Flow

• Pulsatile flow is also abnormal in veins.
• Associated with:
  • Arteriovenous fistulae
  • Systemic venous hypertension:
    • Right heart failure
    • Tricuspid insufficiency
    • Pulmonary hypertension

Diagnosis: Abnormal Alternating Antegrade and Retrograde Flow

• Usually the result of valve damage, which allows for retrograde flow.
• Retrograde flow can occur with normal respiration and/or upon provocative maneuvers.

Sequela of DVT: Skin Changes

• Edema
• Redness
• Brawny discoloration in the gaiter zone
• Phlegmasia alba dolens
• Phlegmasia cerulea dolens

Sequela of DVT: Venous Insufficiency

• Primary - hereditary, not related to DVT
• Secondary – Associated with repeated episodes of DVT, pregnancy, or obesity

Disorders

• May-Thurner syndrome: Compression of the left common iliac vein (and potential thrombosis) by the right common iliac artery.
• Phlegmasia alba dolens: Extensive iliofemoral DVT that causes marked swelling of the lower extremity with pain, pitting edema, and blanching (also called milk leg or white leg).
• Phlegmasia cerulea dolens: Extension of phlegmasia alba dolens that causes even more massive swelling, more severe pain, and cyanosis of the limb; venous outflow is completely obstructed and may result in arterial insufficiency and venous gangrene.
• Most serious sequela of DVT is pulmonary embolism.

Sequela of Venous Insufficiency Caused by Chronic DVT: Venous vs Arterial Ulcers

Incidental Findings

• Nonvascular findings:
  • Cysts (Baker’s)
  • Hematomas
  • Edema
  • Abscesses
  • Enlarged lymph nodes
  • Tumors
• Vascular findings:
  • Aneurysms
  • Pseudoaneurysms
  • Arteriovenous fistulas
  • Significant arterial disease

Other Imaging Procedures

• Conventional contrast venography (uncommon).
• Computed tomography venography (used to define the status of iliac veins).
• Magnetic resonance venography (used to detect DVT, most useful when used above the inguinal ligament).

Treatment

• Primary treatment is anticoagulation (Heparin and Warfarin used in varying degrees, Low-molecular weight Heparin).
• Other treatment measures:
  • Gradient elastic stockings (compression stockings).
  • Thrombolytic agents and thrombectomies.
  • Venal caval interruption device (Greenfield filter).