Deep Venous Thrombosis




Venous thromboembolism (VTE) is an important worldwide clinical entity. It includes asymptomatic deep venous thrombosis (DVT), symptomatic DVT, and pulmonary embolism (PE). Each year, DVT and PE affect 1 to 2 per 1000 people in the United States. In persons more than 80 years old, the incidence of DVT increases to 1 in 100. One third of the people who had DVT may go on to develop long-term complications (e.g., postthrombotic syndrome) with symptoms of swelling, pain, and discoloration of the affected limb. Recurrent DVT occurs in one third of patients within 10 years of the initial diagnosis. Approximately 60,000 to 100,000 people die of DVT or PE each year in the United States.


Diagnostic Methods


Clinical and ancillary findings are useful for the diagnosis of DVT. Clinical scoring systems such as the Wells score can be used to select patients for an appropriate diagnostic test. Noninvasive tests, such as the D-dimer test, and plethysmography may be used for diagnosis of DVT. However, sensitivity varies, and specificity is poor ( Table 49-1 ). The definitive diagnosis depends on identifying the presence, location, and extent of the thrombus on imaging studies. Ultrasonography and color Doppler imaging are commonly used; computed tomography venography (CTV) and magnetic resonance venography (MRV) play significant roles in identifying pelvic, abdominal, and chest DVT. Ascending venography has little role in the diagnosis of DVT, although it is used in therapeutic interventions (see Table 49-1 ).



Table 49-1

Diagnostic Tests for Deep Venous Thrombosis




























Test Advantages Disadvantages
D-dimer test Rapid
Inexpensive
Variable sensitivity
Poor specificity in certain patient populations
Ultrasound Relatively inexpensive
Can be performed at bedside
Highly sensitive for above-knee symptomatic DVT
Operator dependent
Poor specificity for calf vein and pelvic vein DVT
CT venography Highly sensitive and specific for central and pelvic vein DVT
Can be used in patients with inherent contraindications for MRI
Expensive
Radiation exposure
Adverse reactions to contrast material
MRV Highly sensitive and specific for central and pelvic vein DVT
Can be used in patients allergic to iodinated contrast material
Both noncontrast and gadolinium-enhanced studies possible
Expensive
Poor availability
Cannot be used in patients with pacemakers or aneurysm clips and in those who are claustrophobic
Gadolinium contraindicated in patients with renal failure
Ascending venography Highly sensitive and specific for DVT, including calf vein DVT Invasive
Poor availability
Radiation exposure
Adverse reactions to contrast material
Risk of thrombophlebitis and contrast material extravasation

CT, Computed tomography; DVT, deep venous thrombosis; MRI, magnetic resonance imaging; MRV, magnetic resonance venography.


Ultrasonography


Ultrasonography is the imaging test of choice for assessment of DVT in the extremities. This technique is recommended for symptomatic patients in whom the suspicion of acute DVT is high. Grayscale ultrasound is coupled with Doppler (duplex ultrasound) imaging for an accurate assessment of the venous system. This approach has greater than 95% sensitivity and specificity for detecting above-knee DVT.


Technique


The deep and superficial veins of the extremities are usually examined from proximal to distal locations (i.e., from the common femoral vein to the tibial veins or from the subclavian vein to the forearm veins). At each location, the vein is compressed directly with the ultrasound probe to assess compressibility. In addition, Doppler evaluation of the vein is performed (either with or without color flow imaging) to assess presence of flow changes to respiration and cardiac motion and the response to distal compression. Normal veins are compressible and demonstrate an anechoic lumen ( Fig. 49-1 ). The venous flow is phasic with respiration and shows an augmentation response to distal compression ( Fig. 49-2 ). Upper extremity veins often demonstrate flow variations secondary to cardiac pulsations. This phenomenon is often observed in the jugular, subclavian, and axillary veins. Deep inspiration may collapse a normal subclavian or jugular vein.




Figure 49-1


Compression ultrasound study.

Grayscale ultrasound examination shows anechoic lumen with thin walls of right femoral vein (FV MID; left arrow ). The vein is compressible (W/COMP; right arrow ), a finding suggesting that the vein is patent.



Figure 49-2


Spectral Doppler evaluation of the left common femoral vein (CFV).

Imaging shows respiratory flow variations ( arrowhead, flow during expiration; vertical arrow, flow during inspiration) and augmentation response (Aug; horizontal arrow ) to distal compression.


Findings


An enlarged vein that is noncompressible and demonstrates low-level echoes within the lumen is diagnostic of acute DVT ( Fig. 49-3 , A ). Color flow and Doppler imaging techniques demonstrate no flow within the lumen (see Fig. 49-3 , B ). The response to distal compression is blunted. Partial thrombosis of the vein manifests as a partially compressible vein with partial flow noted on color flow imaging ( Fig. 49-4 ). Subacute thrombosis is depicted as a normal-caliber vein that is noncompressible or partially compressible with a moderately echogenic lumen and an absence of color flow or Doppler signal. Partial recanalization of the thrombus results in the appearance of flow channels within the thrombus; these channels are best observed on color flow or power Doppler imaging ( Fig. 49-5 ). As the thrombosis becomes chronic, the caliber of the vein becomes small, with little or no flow. Calcification of the venous wall indicates chronic DVT and may be seen as a highly echogenic focus with or without distal acoustic shadowing.




Figure 49-3


Acute deep venous thrombosis on ultrasound.

A, Grayscale ultrasound examination of the right common femoral vein (CFV) demonstrates an enlarged vein (arrows) with low-level intraluminal echoes . The vein is noncompressible (N/C). B, Corresponding color flow and spectral Doppler image shows an absence of color flow and spectral tracing that suggests no flow within the vein.



Figure 49-4


Partial thrombosis of right popliteal vein (POPV) on color flow imaging.

Wall-adherent mixed echogenic thrombus (top arrow) with minimal peripheral flow (bottom arrow) is visible.



Figure 49-5


Partial recanalization of thrombus.

A, Grayscale ultrasound examination shows multiple intraluminal septa resulting from recanalized thrombus. B, Corresponding color flow image shows partial flow within the thrombus. CFV, Common femoral vein.


Upper extremity DVT has similar imaging characteristics. The absence of normal cardiac pulsations and of a response to deep inspiration may suggest the presence of DVT in the proximal veins.


Pearls and Pitfalls





  • Ultrasound may identify other causes of leg pain, such as a ruptured or unruptured Baker cyst, hematoma, and tendon injury.



  • Visualizing the intrathoracic and abdominopelvic veins is often difficult. Proximal (or central) venous compression or thrombosis may be suspected when respiratory phasic variations in the distal veins are absent (see the later section on May-Thurner syndrome).



  • When DVT is detected, the examiner must assess its proximal extent because pelvic DVT is more often associated with PE.



  • The sensitivity of duplex ultrasound in detecting symptomatic DVT is greater than 95%; however, it falls to 50% for detection of asymptomatic DVT. When the ultrasound study result is negative in patients with a high clinical suspicion of DVT, a repeat ultrasound study 1 week later is recommended.



Computed Tomography Venography


CTV allows visualization of central thoracic and abdominopelvic veins that are often obscured on ultrasound. One of the main advantages of CTV is that the study can be combined with computed tomography pulmonary angiography (CTPA) without the requirement of additional intravenous contrast material. These protocols allow 20% higher detection of VTE compared with CTPA alone. The extent of the computed tomography (CT) scan ranges from the popliteal fossa to the groin or the pelvis. The scan may be extended to the upper abdomen if thrombosis of the inferior vena cava (IVC) or gonadal or renal veins is suspected.


Technique


CTV may be performed following intravenous injection of diluted (10%) iodinated contrast material in the foot veins or upper extremity veins to assess regional venous thrombosis. This technique is referred to as direct CTV and is rarely practiced now, but it can be useful when other studies are indeterminate. Indirect CTV refers to CT assessment of the regional and nonregional veins following intravenous administration of regular-strength contrast material. The veins are imaged during equilibrium phase (approximately 3 minutes following the injection of contrast material). Images are reconstructed at 5- to 7.5-mm slice thickness with no interslice gap. Venous enhancement is considered adequate when the attenuation in the vein is higher than in the adjacent muscles; the enhanced veins rarely achieve an attenuation of more than 150 HU.


Findings


CTV allows direct visualization of thrombus in the vein as a filling defect within the contrast-filled lumen ( Fig. 49-6 ). When thrombus fills the entire lumen and extends for a few CT slices, that segment of the vein fails to enhance with contrast material. Additional findings of acute thrombosis include an enlarged vein, rim enhancement of the vein (see Fig. 49-6 ), and perivenous edema or stranding. The sensitivity and specificity of CTV in detecting above-knee DVT are 90% to 95% compared with those of venous ultrasonography. Chronic thrombosis may be seen as nonenhancing small-caliber vein or intraluminal webs with enhancement of recanalized channels; the presence of calcification within the venous wall is diagnostic of chronic DVT ( Fig. 49-7 ).




Figure 49-6


Right common femoral vein thrombosis on computed tomography venography.

The vein (arrow) is enlarged, with an intraluminal filling defect and rim enhancement.



Figure 49-7


Chronic deep venous thrombosis of the left popliteal vein on computed tomography venography.

Calcification of the vein (arrow) with faint intraluminal webs is visible.


Pearls and Pitfalls





  • Excellent visualization of the central and peripheral veins makes CTV an optimal test for the diagnosis of DVT.



  • CTV allows detection of other leg disorders such as popliteal cysts, iliopectineal bursitis, joint effusions, and intramuscular hemorrhage.



  • Radiation exposure can be minimized by limiting the study to the thighs and scanning at lower peak kilovoltage.



  • Inadequate enhancement of the veins can be minimized by using autotriggered scanning while keeping a region of interest in the femoral vein with a threshold of 60 HU. Larger volume of contrast material, low peak kilovoltage (80 kVp), and reconstruction at 50 keV on a dual energy scanner allow better visualization of the veins on indirect CTV.



  • Image visualization at narrow window length and coronal reformations are also helpful to delineate the thrombus and its longitudinal extent.



Magnetic Resonance Venography


MRV is less commonly used for detection of lower extremity DVT. It is often used to assess the central veins of the thorax and body. It is equally sensitive and specific for detection of DVT in both the central and peripheral veins. MRV can be performed either with or without the use of gadolinium. Noncontrast MRV methods include bright-blood techniques such as time of flight (TOF) imaging, true fast imaging with steady-state precession (true FISP), and electrocardiogram-gated three-dimensional fast spin echo (FSE) imaging and black-blood techniques such as FSE T2-weighted and double inversion recovery FSE imaging. Contrast-enhanced MRV techniques use three-dimensional gradient echo techniques similar to magnetic resonance angiography (MRA) for venous phase imaging. Rarely, direct MRV (similar to direct CTV) is performed with diluted (2%) gadolinium. Blood pool contrast materials (e.g., gadofosveset trisodium) are best suited for venous imaging.


Technique


The axial two-dimensional TOF technique is employed for abdominopelvic and lower extremity veins, with a saturation band applied superiorly to prevent artifacts from the arterial inflow. True FISP imaging is usually performed in the coronal plane for the body and in the axial plane for extremities. Images are acquired in 3- to 5-mm slice thickness. Contrast-enhanced MRV is usually performed in the coronal plane.


Findings


On bright-blood techniques and contrast-enhanced MRV, thrombus is seen as a filling defect within the vein ( Fig. 49-8 ). Long segment thrombosis is best appreciated on coronal or sagittal images and is visualized as discontinuity of the vessel. However, the venous wall may enhance on contrast-enhanced MRV, thus giving a tram-track appearance ( Fig. 49-9 ). Perivenous edema is rarely appreciated, but it can be seen on T2-weighted FSE sequences. On black-blood techniques, thrombus is seen as a mass of low signal intensity within the lumen of the vein. Chronic thrombus is seen as a small-caliber, nonenhancing vein with or without venous stenosis. Collateral veins are often seen bypassing the obstructed vein.




Figure 49-8


Partial thrombosis of the inferior vena cava (IVC) on magnetic resonance venography (MRV).

Bright-blood technique (true fast imaging with steady-stage precession) ( A ) shows low signal intensity on the right half (arrow) of the IVC that does not enhance on contrast-enhanced MRV ( B ), a finding suggesting partial thrombosis of the IVC.



Figure 49-9


Left renal vein thrombosis on magnetic resonance venography (MRV).

Contrast-enhanced MRV shows the tram-track appearance of the left renal vein (arrow) with an intraluminal filling defect secondary to tumor thrombus from left renal cell carcinoma.


Pearls and Pitfalls





  • Flow directional abnormalities may result in signal void on TOF sequences. Additional imaging either with true FISP or contrast-enhanced MRV may be required to limit false positive diagnosis of DVT. On the other hand, the flow directional nature of TOF sequence can be utilized for advantage while assessing the hemodynamic significance of venous stenoses as collateral veins may show flow directional abnormalities (see the later section on May-Thurner Syndrome).



  • True FISP imaging can be combined with background suppression to provide better contrast resolution of the veins. During contrast-enhanced MRV, delayed (2 minutes), axial fat-saturated gradient echo, high-resolution T1-weighted images allow assessment of partial and wall-adherent thrombus.



  • Similar to CTPA, MRV can be combined with pulmonary MRA, especially with the use of blood pool contrast materials.



Ascending Venography


Although ascending venography remains the gold standard, it is rarely performed for the diagnosis of DVT because it has been replaced by ultrasonography for extremity DVT. Ascending venography has 95% specificity and 100% sensitivity for thrombi measuring 0.5 cm or more, and it is still the test of choice for detection of below-knee DVT. It is used in interventional procedures such as thrombolysis, placement of an IVC filter, and revascularization of venous occlusion.


Technique


Upper extremity venography is performed with the patient supine, with hands abducted and supinated. A superficial vein in the dorsum of the hand is accessed with an 18-gauge needle. A blood pressure cuff that is inflated to nearly systolic pressure or a tourniquet is applied in the upper arm, and diluted (240 mg iodine/mL) contrast material is injected. Multiple overlapping fluoroscopic images are obtained for the forearm and arm. The central veins are imaged while the contrast material is injected and the blood pressure cuff is deflated. Proximal venous access is often helpful for visualizing the central veins.


Lower extremity venography is best performed with the patient in the reverse Trendelenburg position at 30 to 60 degrees. The limb examined is kept nonweight bearing, and a dorsal foot vein is cannulated with an 18-gauge needle. A tourniquet applied at the ankle helps direct contrast material in to the deep venous system. Diluted contrast material (240 mg iodine/mL) is injected to a volume of 50 to 100 mL, and serial fluoroscopic images are obtained of the extremity. Pelvic veins are best imaged with the patient in the supine position.


Descending venography is performed for assessing venous insufficiency. In this procedure, a short sheath is placed in the common femoral vein, the patient is positioned at 60 degrees in the reverse Trendelenburg position, and 20 mL of contrast material is injected. Retrograde flow into the femoral and saphenous veins indicates the presence of venous reflux.


Findings


As with CT, acute thrombus is seen as a filling defect within the contrast-filled lumen ( Fig. 49-10 ). The vein may be enlarged, and collateral veins may be visualized. Chronic thrombosis results in nonvisualization of the vein, with multiple collateral veins bypassing the occluded vein. Recanalized veins may appear as linear channels within the expected course of a vein.


Aug 7, 2019 | Posted by in CARDIOVASCULAR IMAGING | Comments Off on Deep Venous Thrombosis
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