Current DVT imaging

Current DVT Imaging Douglas S. Katz, MD and Man Hon, MD

Accurate diagnosis of deep venous thrombosis (DVT) is very difficult, and imaging plays a crucial role in the diagnosis or exclusion of DVT. The initial test of choice for diagnosis of acute thigh as well as upper extremity DVT is ultrasound, because of its high accuracy, relatively low cost, portability, and lack of ionizing radiation. In patients who are undergoing CT pulmonary angiography for suspected pulmonary embolism, CT venography can be performed as part of the examination, for comprehensive evaluation of the venous system in the legs, abdomen, and pelvis. MR has a problem-solving role, and conventional venography is now limited to specific scenarios including evaluation of central DVT in the upper extremities, as a prelude to intervention for thrombolysis/thrombectomy, and prior to placement of an inferior vena cava filter. This article discusses the imaging findings of DVT, and the role of these imaging examinations in the evaluation of patients with suspected DVT. © 2004 Elsevier Inc. All rights reserved.

ccurate clinical diagnosis of deep venous thrombosis (DVT) is notoriously difficult. The same is true of pulmonary embolism (PE). PE and DVT are part of the same process, venous thromboembolism (VTE). Most DVT is believed to begin in the calves, and about 90% of PE is believed to originate in the deep veins of the lower extremities and pelvis. Up to twothirds of patients with lower extremity DVT (LEDVT) are asymptomatic, yet there are significant sequelae of DVT in addition to PE, including chronic venous disease. Further complicating matters, PE may also be clinically silent in a large minority of patients with DVT,1,2 and fewer than 50% of patients with signs and symptoms suggesting DVT actually have it. For several decades, contrast (or “conventional”) venography was the imaging test of choice for confirmation or exclusion of DVT in the lower extremities, pelvis, and inferior vena cava.3 Clot was identified as a filling defect or implied by complete nonfilling of a vein (Fig 1). Although this became the “gold standard” examination for DVT, there were problems in a small percentage of patients, including access difficulties, pain, contrast reactions, and paradoxically postprocedure DVT.3 Additionally, 5% to 10% or more of studies were technically inadequate, and there was interobserver disagreement in up to 10% of examinations.3 With the introduction of lower extremity sonography (US) in the late 1980s, conventional venography for DVT was decreasingly used, and now is almost never per-

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From the Department of Radiology, Winthrop-University Hospital, Mineola, NY. Address reprint requests to Douglas S. Katz, MD, Department of Radiology, Winthrop-University Hospital, 259 First Street, Mineola, NY 11501. © 2004 Elsevier Inc. All rights reserved. 1089-2516/04/0702-0003$30.00/0 doi:10.1053/j.tvir.2004.02.002

formed as a purely diagnostic examination for the lower extremities, although it has occasional uses especially in the upper extremities/thorax. US has become the imaging test of choice for patients with signs and symptoms suggesting LEDVT, because of its high accuracy for evaluation of the thighs, as well as its relatively low cost, portability, repeatability, accessibility, and lack of ionizing radiation.

US for Suspected DVT Technique and Findings Current techniques still rely primarily on compression sonography. DVT is absent if pressure from the transducer completely collapses the underlying vein, but is present if the vein does not collapse (Fig 2). Transverse images of the common femoral, superficial femoral, and popliteal veins are obtained along the course of these vessels, supplemented by sagittal color and spectral Doppler images. Typically, a 5 or 7.5 MHz linear transducer is used. Color and spectral Doppler are especially helpful in obese patients and when imaging deeper areas, eg, the superficial femoral vein in the adductor canal.4 In acute DVT, venous distension may be present, although the echogenicity and visibility of thrombus is variable.5 Additionally, alternate diagnoses, such as hematoma and ruptured Baker’s cyst, can also be identified in patients without DVT.

Accuracy and Pitfalls High accuracy of US for diagnosis or exclusion of DVT in the thighs of symptomatic patients has been reported in multiple studies, which approaches 100%.4-6 However, the study can be difficult or limited in patients with obesity, marked swelling, and overlying casts. There is controversy over whether both legs should be routinely imaged if only one side is symptomatic.6,7 In addition, some authors have advocated a limited study with imaging at the groin and knee only,8 but the incidence of clot isolated in the thigh to the superficial femoral vein (SFV) is as high as 20%.9-11 Duplication of the SFV is very common, occurring to varying degrees in up to 50% of the population (Fig 1). This is a potential pitfall of sonography, because if clot is present in one of the two limbs of the vein, and only the patent limb is identified, the study will be falsely interpreted as negative for SFV DVT.12,13 Correctly recognizing chronic DVT (and acute superimposed on chronic DVT) remains problematic on all imaging modalities. Up to one-half of patients on follow-up US for acute DVT will have residual abnormalities.14 Findings of chronic DVT include increased clot echogenicity, irregularly thickened venous walls, small caliber veins, and collateral veins. Chronic DVT may be indistinguishable by sonographic appearance alone as the echogenicity of chronic clot is variable, and other features of chronic DVT may be absent.5,14,15 Differentiating

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reported in asymptomatic patients, especially in those at high risk for DVT (i.e., orthopedic patients) when compared with conventional venography. This is presumably because the clots in these patients are usually smaller and nonocclusive, and because of the much higher incidence of calf DVT.5,18

Calf Sonography US of the calves (and pelvis) for DVT is not routinely performed, because of the low reported accuracy and high incidence of nondiagnostic studies.6,19 However, focal calf pain can be evaluated with a directed US with some success (Fig 3). The incidence, significance, and therapy of isolated calf DVT remains controversial. Some authors recommend follow-up thigh sonography at 1 week if the initial study is negative, so as to not miss the 20% of calf DVT that reportedly can propagate to the thighs.8,20 Clearly, the incidence of DVT isolated to the calves is not trivial, and some of these patients will have concurrent PE.10,21

Upper Extremity DVT Imaging

Fig 1. Patient with acute right leg pain and myeloma. Conventional venography image shows DVT in both limbs of a duplicated superficial femoral vein.

postphlebitic syndrome from chronic DVT is important in symptomatic patients. Repeat sonography is very useful in distinguishing between these two entities. Also, in patients with DVT who become asymptomatic following therapy, obtaining a repeat US to serve as a new baseline is suggested for most patients.14

Role of Sonography in Patients without Symptoms of DVT There is much controversy as to the utility of US in patients with suspected PE but without signs or symptoms of DVT.7,11 Previous algorithms have included US following indeterminate ventilation-perfusion scans or after negative or nondiagnostic computed tomographic pulmonary angiography (CTPA) studies.10 Some studies have demonstrated a high incidence of DVT in such patients, whereas others have shown DVT in only a minority of patients.11,16,17 We routinely perform combined CT venography and pulmonary angiography (CTVPA) whenever PE is suspected, in lieu of an isolated CTPA or isolated lowerextremity US. A limitation of US is that a negative examination imparts no information as to the presence or absence of PE. If the study is positive, the presence of PE can be assumed from a therapeutic standpoint, however, the extent of clot in the thorax is not known. Much poorer results for DVT detection on US have been

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The incidence of upper extremity DVT is increasing, because of the widespread use of central venous catheters and pacemakers. Upper extremity DVT (UEDVT) may also be related to hypercoagulability as well as low-flow states, and occasionally to “effort” thrombosis in athletic young people, especially men, with thoracic outlet syndrome.22 The signs and symptoms of UEDVT include pain and swelling, although less than half the time DVT is actually present.23-25 The exact relationship to PE is not known, but the risk is estimated at up to 15%.25 The initial test of choice for UEDVT is US, which is nearly 95% accurate. In contrast to lower extremity US, usually only the symptomatic side is studied.5 The axillary, brachial, and internal jugular veins are imaged with compression US, complemented with color and spectral Doppler. The subclavian vein, however, cannot be readily compressed because of the overlying clavicle, and color Doppler is therefore relied upon. The superior vena cava and more central portions of the brachiocephalic veins cannot be routinely visualized. Therefore, secondary signs are used to infer the presence of more central clot, including absence of cardiac pulsatility and respiratory variation.25

Combined CTVPA CTPA has become the noninvasive test of choice for suspected PE at many centers. Because PE and DVT are aspects of the same disorder, the deep venous system, from the inferior vena cava to the calf veins, can be easily imaged for concurrent DVT following CTPA, demonstrating the overall burden and distribution of clot. This combined CTVPA protocol requires no additional IV contrast and only a few extra minutes.10,26 CT venography (CTV) is useful, even if the CTPA portion of the study is positive, for identifying coexistent DVT in the thighs and pelvis, which reportedly increases the risk of additional embolic episodes. CTV may salvage the occasional nondiagnostic or limited CTPA study.10

Technique and Findings Beginning at 3 to 3.5 minutes after the start of IV contrast injection for CTPA, 5 mm or 10 mm images are obtained every KATZ AND HON

Fig 2. US of acute DVT. Transverse sonographic images show that the right common femoral vein does not collapse with compression (arrow, right image) indicating a DVT. Clot was present to the level of the right popliteal vein. CT pulmonary angiography subsequently demonstrated pulmonary embolism (not shown).

Fig 3. Focal left calf pain. There is a thrombosed deep calf vein on lower extremity sonography (arrow). Note the absence of Doppler signal. CURRENT DVT IMAGING

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Fig 4. CTVPA revealed central bilateral pulmonary emboli (not shown) and acute left lower extremity DVT from the left common femoral vein to the calf veins. At the level of the distal thighs, note left proximal popliteal DVT (straight arrow) and adjacent soft-tissue edema (curved arrows).

Fig 5. Left calf DVT is shown (arrow), from the same CT venography examination as in Fig 3.

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Fig 6. CTVPA demonstrated extensive pulmonary emboli and pulmonary infarctions (not shown), as well as DVT of the right leg and calf. Use of a narrower CT window helps to show the right superficial femoral DVT (straight arrow). Note the subcutaneous edema (curved arrows).

Fig 7. Right calf DVT (arrow). Note the swelling of the right calf compared with the left. CURRENT DVT IMAGING

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Fig 8. Pregnant female with US documented femoral DVT; MRI was performed to assess for pelvic clot. Nonenhanced gradient-recalled echo axial image shows flow in the right external iliac vein (straight arrow), but no flow in the left external iliac vein (curved arrow), consistent with DVT.

4 cm, from the diaphragm to the ankles. Clot is identified as a filling defect within a deep venous structure. In acute DVT, there is often expansion of the vein, and perivenous edema may be seen, along with enhancement of the venous wall (Figs 4-7).10,26,27 We prefer this technique as a “survey” study, rather than contiguous helical images of the entire abdomen, pelvis, thighs, and calves, because our goal is to identify potentially significant clot burden. We believe the minimally increased yield of a helical acquisition is more than offset by the significantly larger number of images that need to be reviewed and stored. More importantly, there is a significant increase in radiation dose if such a protocol is used.10,26,27

diagnostic yield of venous thromboembolism by up to 20%.10,29-31 In one recent report of 1745 patients, there was DVT on 167 examinations (9.6%), and 23% of these had iliac vein and/or inferior cava involvement.30 The most common pitfall of CTV remains mixing artifacts. As with other imaging modalities, accurate detection of chronic DVT remains problematic, and has not been well studied to date. A small percentage of studies are nondiagnostic, especially in patients with poor cardiac function and/or significant lower extremity atherosclerotic disease.10,28 In these patients, if CTPA is negative or additional information regarding the lower extremities is required, US is then recommended.

Accuracy and Pitfalls High accuracy for thigh DVT identification or exclusion on CTV has been reported in several series.27-29 In one study of 308 patients, there was 97% sensitivity and 100% specificity compared with US.27 The addition of CTV increased the overall

Magnetic Resonance Imaging for DVT Magnetic resonance imaging (MRI) for DVT evaluation was introduced in the early 1990s, and high accuracy has been shown compared with conventional venography. A variety of

Fig 9. Axial gradient-recalled echo MRI from the same examination as shown in Fig 8 confirms absence of venous flow in the left common femoral vein (arrow).

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Fig 10. Circumaortic left renal vein. Selective left renal venogram, as a prelude to inferior vena cava filter placement, shows a circumaortic left renal vein, which necessitated placement of the filter below the left renal vein.

techniques have been described, including the use of spin-echo, gradient-recalled echo, and gadolinium-enhanced sequences.32,33 Findings of DVT include absence of venous flow and filling defects, as well as perivenous inflammation in a minority of patients, analogous to what is seen on CTV. Also analogous to CTV, MRI may reveal ancillary findings that may be contributing to the DVT.33 Although not well studied, MR may be superior to US and CTV for determination of the chronicity of a DVT.15 The disadvantages of MRI include its relatively expense and lack of portability. MRI can be used as a problem-solving technique, especially for imaging the pelvic veins (Figs 8 and 9). The true frequency of pelvic DVT is underestimated with US, and in certain patients—those who are pregnant, or who have undergone pelvic surgery or have a pelvic malignancy—DVT may start in the pelvis and then propagate down into the thighs.22,34 Gadolinium enhancement is not required for LEDVT MRI detection, however, in situations where contrast is given for MRI pulmonary angiography, concurrent axial gradient-recalled images of the abdomen, pelvis, and legs can be beneficial. MRI is also advantageous for imaging suspected central thoracic venous thrombosis. In contrast to US, the brachiocephalic veins and the superior vena cava are readily identified, and causes of thrombosis such as a central mass are shown.33

Nuclear Medicine Imaging for DVT Over the past several decades, a variety of nuclear medicine techniques, including iodine-123-labeled fibrinogen and platelets, have been tried for imaging DVT. None of these techniques have been widely adopted into clinical practice for multiple reasons. The most recently introduced agent, Tc99m Apcitide, is a small synthetic peptide that has a strong affinity for binding CURRENT DVT IMAGING

to activated platelets.35 This particular agent, which has recently been tested in phase III trials, may have a role in the near future for distinguishing acute from chronic DVT. In a subset of patients with DVT that was believed to be acute, Tc99m Apcitide achieved a sensitivity of 90%.35 Although there are concerns regarding its availability and cost, hopefully this radiopharmaceutical and future agents will have a problem-solving role in the evaluation of DVT.

Current Role of Contrast Venography Diagnostic contrast venography for evaluation of DVT is now limited to specific scenarios: indeterminate US examination in the obese or markedly swollen leg, evaluation of suspected calf vein DVT in patients with negative or indeterminate US where the finding would change patient management, evaluation of central DVT in the upper extremities, as a prelude to intervention for thrombolysis/thrombectomy, and before placement of inferior vena cava (IVC) filters. Diagnostic venography of the IVC is performed to evaluate for presence of thrombus and for evaluation of venous anomalies, which may alter the approach and positioning of the IVC filter. In addition, the dimensions of the IVC where the filter is to be deployed can determine the type of IVC filter to be used. Selective left renal venography can be beneficial to evaluate for a circumaortic left renal vein (Fig 10), since the incidence of this venous anomaly may be as high as 11%.36,37

Summary Sonography is the test of choice for the evaluation of suspected LEDVT. Although it has very high accuracy in symptomatic patients for the deep thigh veins, it is less accurate for the calves

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and the pelvis. In patients with suspected PE, CTVPA permits comprehensive assessment for PE and DVT, and offers significant advantages over CTPA alone. MRI can be used as a problem-solving study in selected situations. The newest radiopharmaceutical, Tc99m Apcitide, may permit accurate differentiation of acute versus chronic CT, which is problematic on the other modalities. Conventional venography is primarily of historical interest as purely a diagnostic examination. However, it is still performed as a road-mapping technique immediately before IVC filter placement for delineation of anatomy. Venography of both the lower and upper extremities is routinely performed as part of a variety of therapeutic procedures for DVT, including thrombolysis, percutaneous thrombectomy, angioplasty, and stent placement.

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