Chapter 17. Deep Venous Thrombosis

Ultrasound evaluation for deep venous thrombosis (DVT) is one of the 11 core ultrasound applications for emergency physicians as listed in the 2008 American College of Emergency Physicians guidelines.1 This evaluation typically consists of a limited compression ultrasound of the proximal lower extremities. Although different from a typical “duplex” examination performed in many vascular laboratories in the United States, which consists of a combination of whole leg compression ultrasound and Doppler ultrasound, limited compression ultrasound has been widely studied as the initial investigative tool for the diagnosis of DVT.2,3

If left untreated, DVT can lead to significant morbidity and mortality, including pulmonary embolism (PE) and post-phlebotic syndrome. The annual incidence of venous thromboembolism is approximately 1 in 1,000 and increases with age. Since two-thirds of patients with venous thromboembolism are initially diagnosed as proximal lower extremity DVT, this leads to an annual incidence in the United States of DVT of approximately 200,000 cases.4 Without treatment, 50% of these will progress to PE with a resultant 30 days mortality of approximately 15%.4 With treatment, the complications of DVT are reduced to less than 5%. However, anticoagulation causes major bleeding in almost 2% of patients and mortality in 0.2%, so treatment should be limited to only those diagnosed with the disease.5 Therefore, diagnostic strategies need to have a high sensitivity and specificity.

The vast majority of DVTs (>90%) are diagnosed in the proximal veins of the lower extremity (common femoral vein, superficial femoral vein, and popliteal vein). The iliac veins account for about 2% of DVTs.6 Upper extremity veins account for a small share of DVTs, unless a venous catheter is present.

The approach to isolated calf vein DVTs is still a source of great controversy. The tendency of these to propagate proximally is at the center of the debate concerning the best approach, including (1) repeat ultrasound in 1 week, (2) D-dimer testing for patients with a negative limited compression ultrasound, and (3) a single whole leg ultrasound.3 Superficial thrombophlebitis had been thought to never progress to DVT, though some studies are challenging that and even suggesting treatment for superficial thrombophlebitis involving the proximal greater saphenous vein.7

Clinical signs and symptoms of DVT consist of leg swelling and tenderness; however, only about 20% of patients who are clinically suspected of having a DVT actually have one. High-sensitivity D-dimer assays, when negative, have been shown to help rule out DVT in patients with a low clinical suspicion.8 Ultrasound of the proximal lower extremities has become the gold standard imaging test for diagnosing DVT. Most current algorithms for assessing patients with suspected lower extremity DVT involve using a combination of clinical suspicion, high-sensitivity D-dimer assays, and compression ultrasound of the lower extremity.8,9

Emergency medicine providers are uniquely qualified to use a combination of clinical suspicion, lab testing, and limited compression ultrasound to rapidly diagnose patients with DVT and safely discharge low-risk patients who do not have evidence of DVT.

The clinical indications for performing a venous ultrasound examination are as follows:

• Suspicion of a lower extremity DVT
• Suspicion of an upper extremity DVT

Suspicion of a Lower Extremity DVT

Virchow's triad—hypercoagulability, venous stasis, and vessel injury—is the main risk factor for developing a DVT. The pathophysiology behind the development of venous thrombosis is not as well understood as arterial thrombosis, although both involve similar elements of the coagulation cascade. Once thrombus has occurred, reorganization of the clot begins. This process allows clefts to form between the clot and the vein wall, beginning about 1 week after initial clot formation; this is thought to be when the risk of PE is greatest. Over the next several weeks, the clot may be lysed and recanalized, leaving a thickened intima.

Only about half of all patients with DVT have any noticeable signs or symptoms. Risk factors for DVT are listed in Table 17-1. The combination of risk factors, physical examination findings, and clinician judgment has been developed into a clinical prediction model (Table 17-2).8,9 This clinical prediction model is often combined with a high-sensitivity D-dimer assay to decide who should undergo ultrasound evaluation for DVT.

There are different views about how ultrasound should be used to assess for DVT. Historically, whole leg ultrasound has been performed in vascular laboratories. This is often referred to as duplex ultrasound, which combines compression ultrasound with multiple measurements using color and pulse wave Doppler. The entire leg is usually scanned, with measurements taken every few centimeters from the inguinal ligament down to and including the calf veins. This technique is time consuming, taking an average of 37 minutes to perform in one study.10

Another school of thought is to perform limited compression ultrasound concentrating on the common femoral vein and the popliteal vein. This technique seems best suited for emergency care providers because it can be performed rapidly at the patient's bedside and has been shown to be safe and effective. One study compared limited compression ultrasound to contrast venography in 220 patients clinically suspected of having DVT. Limited compression ultrasound was found to be 100% sensitive and 99% specific for clinically relevant DVT (popliteal and above).11 Numerous studies since then have confirmed the high sensitivity and specificity of a limited compression ultrasound technique.12–17 Others have raised a theoretical concern that there may be isolated DVT present in the superficial femoral vein that could be missed by this technique, but the preponderance of data do not support this belief.18

Several large studies have followed outcomes of patients at 3 and 6 months looking for venous thromboembolic events. They have all pointed to the safety of limited compression ultrasound for the diagnosis of DVT. A 2002 study performed a limited compression ultrasound on 1756 patients with suspected DVT.19 They combined this with a high-sensitivity D-dimer assay and limited repeat ultrasound in 1 week for patients with a positive D-dimer. Twenty-two percent of patients were diagnosed with a proximal DVT initially. Of patients with a negative initial ultrasound and D-dimer assay, only 6/828 (0.7%) had a venous thromboembolism at 3 months. Patients with a low pretest probability and a negative D-dimer assay had a 1.8% incidence of venous thromboembolism at 3 months, similar to previous validations of Wells criteria. Patients with a negative initial ultrasound and positive D-dimer had a 3% incidence of DVT in 1 week and an additional 2.1% at 3 months. At no point during this study were calf veins evaluated.

A 2008 study sought to directly compare a limited compression ultrasound evaluation plus D-dimer testing versus a whole leg duplex evaluation.3 It randomized 2098 patients to either approach, with death and DVT/PE at 3 months as the end point. In the limited compression pathway, 0.9% of patients had an untoward event at 3 months versus 1.2% in the whole leg group, which was considered equivalent. The whole leg approach diagnosed 20.4% proximal DVT initially, with 6% calf vein thrombosis; all were treated with anticoagulation. The limited compression ultrasound approach diagnosed 20.8% DVT initially. Of those with a normal initial ultrasound, 30.9% had a positive D-dimer and underwent repeat ultrasound after 1 week. No patients developed PE during this week and none were anticoagulated. After 1 week, an additional 5.5% of patients were found to have a proximal DVT. This study demonstrated that a limited compression ultrasound combined with 1-week repeat ultrasound in patients with a positive D-dimer was equivalent to a whole leg duplex study. This was presumably because the undiagnosed calf vein thrombi that will lead to proximal DVT tend to do so within 1 week. The limited compression ultrasound technique used in these studies included a single compression of the common femoral vein at the inguinal ligament, and two compressions of the popliteal vein, one at the midpoint of the popliteal fossa and the other at the distal popliteal fossa just proximal to its trifurcation.

Several studies have demonstrated that emergency medicine physicians can perform limited compression ultrasound in a few minutes with excellent results.12–17 A 2008 meta-analysis showed that emergency physicians can perform limited compression ultrasound for DVT with accuracy similar to radiology-performed ultrasound.20 In addition, a 2010 study demonstrated that emergency physicians who learned to perform simple compression ultrasound in just 10 minutes had 100% accuracy for diagnosing DVT compared to a whole leg duplex ultrasound performed by radiology.17

Most algorithms for the evaluation of DVT assume ultrasound is an expensive and time-consuming procedure, and so more emphasis is placed on clinical prediction models and D-dimer assays to exclude patients from requiring ultrasound21 (Figure 17-1). However, as emergency physicians become more adept at the technique, a limited compression ultrasound examination can be performed much more swiftly than a D-dimer assay. Using an ultrasound-first algorithm, all patients with clinically suspected DVT (whether low, moderate, or high) can have a limited compression ultrasound examination performed with the plan to have a repeat ultrasound performed in 1 week (Figure 17-2).

Limited compression ultrasound is often of greatest value to emergency providers on evenings, nights, weekends, and holidays when diagnostic imaging services are delayed or unavailable. Although calf vein thrombosis is not assessed with a limited compression ultrasound exam, managing patients based on the results of the limited compression exam has been shown to be safe and effective. A DVT will be diagnosed in about 10–20% of patients who are assessed with limited compression ultrasound, depending on how it is used. Patients who do not have a DVT may have incidental findings that lead to another diagnosis. About 15% of patients suspected of having DVT are eventually diagnosed with a Baker's cyst, knee effusion, or cellulitis, all of which can be visualized with ultrasound.

Suspicion of an Upper Extremity DVT

Upper extremity DVT is thought to account for about 5% of all DVT cases.22 The most common causes of this disease process are malignancy, central venous catheters, and pacemaker wires. The vast majority of upper extremity DVTs is due to indwelling catheters and many occur in the subclavian vein. Other sources of DVT are the axillary and internal jugular veins. External jugular vein thrombosis is extremely rare.

While simple compression ultrasound works well in the lower extremities, the subclavian vein does not lend itself to compression. Therefore, excluding an upper extremity DVT depends on Doppler ultrasound and indirect confirmation of vein patency in a major venous segment. Although it has not been well studied, this suggests that ruling out an upper extremity DVT may be more difficult for less experienced providers. It may be prudent for less experienced providers to use upper extremity ultrasound to rule in the diagnosis of DVT, but not to try to rule it out. It is often straightforward to recognize a positive finding, so it is reasonable to do a brief point-of-care exam. However, patients with a negative point-of-care exam may need further evaluation with a comprehensive ultrasound exam or a CT scan, depending on the experience of the provider and the quality of the initial exam.

Superficial Thrombophlebitis

Although data are lacking, upper extremity DVT is generally considered thrombosis involving the axillary and subclavian veins. Clot in the brachial and basilic veins is generally considered superficial thrombophlebitis, but some believe that this should be treated with anticoagulation. In the leg, the greater saphenous vein is considered a superficial vein, but some believe that thrombosis at this location also requires anticoagulation.7 Superficial venous thrombosis at other locations is considered to be of no significant risk for PE and is treated conservatively and without anticoagulation. On ultrasound, the appearance of superficial venous thrombosis is similar to that of a DVT with failure to compress the vein as the diagnostic criteria.

The upper extremity veins include the radial and ulnar veins, which arise from the palmar venous plexus (Figure 17-3). The radial and ulnar veins run next to the radial and ulnar arteries and join in the antecubital area to form the brachial vein. The brachial vein runs superiorly, usually as two veins on either side of the brachial artery, and flows into the axillary vein approximately where it is joined by the basilic vein. The axillary vein flows into the thorax and becomes the subclavian vein. The subclavian vein is then joined by the internal jugular vein to form the brachiocephalic vein.

The venous system of the lower extremity is quite simple in a proximal to distal examination from the inguinal ligament to the level of the upper calf. Although many clinicians may feel they know the location and anatomy of the femoral vessels, few truly understand the details of the anatomy and variations that may be present. Historically, clinicians are taught that the femoral vein is located just medial to the femoral artery; however, ultrasound examination often reveals that vein and artery overlap rather than lie side by side. When this occurs, the typical arrangement is for the femoral artery to lie on top of the femoral vein.

Proceeding proximal to distal, the first segment after the external iliac vein is the common femoral vein. The first branch of the femoral vein after the inguinal ligament is the greater saphenous vein, which diverges medially and courses superficially down the medial aspect of the leg. The common femoral artery usually bifurcates several centimeters proximal to the bifurcation of the common femoral vein. Often a small innominate vein will be the second branch of the common femoral vein and will course laterally between the superficial and deep femoral arteries. The common femoral vein then bifurcates into the deep femoral and superficial femoral veins. This nearly always occurs within 10 cm of the inguinal crease (Figure 17-4). The name “superficial femoral vein” is deceptive because it is considered part of the deep vein system. There have been efforts to change the name of the superficial femoral vein because inexperienced clinicians have sometimes mistaken reports of thrombus in this location to be outside of the deep venous system.

The deep femoral vein travels deep into the thigh and is difficult to visualize by ultrasound. The superficial femoral vein proceeds distally until it dives into the obturator canal above the knee. In this region, the vein is difficult to access until it emerges behind the knee as the popliteal vein. The popliteal vein travels for about 5 cm in the popliteal fossa before trifurcating into the anterior and posterior tibial veins and the peroneal vein.

Place the ultrasound machine to the right side of the patient, although convenience, clinician comfort, and patient positioning can dictate on which side of the patient it is placed (See Video 17-1). Many ultrasound machines have multiple attached transducers. Select a high-frequency linear array, 5–10 MHz transducer since it provides optimal venous compression and image resolution. Other transducers, such as a large curved array transducer, may be used if a linear array transducer is not available or deeper imaging is required. A curved array transducer, however, may compromise venous compression and superficial image resolution. A linear array transducer is ideal because the linear footprint provides more even compression over the vessel of interest than curved transducers. Controls that select various transducer frequencies and focus for a given transducer are available on most machines, and these settings may be adjusted once the examination has begun to further improve image quality (depending on the depth of the veins being examined).

Raise the head of the bed 15–30° or place the patient in a reverse Trendelenburg position in order to assure that the veins of the lower extremity are filled. Adjust bed height to a level comfortable for the clinician. Use an adequate amount of ultrasound gel during the examination. Finally, dim the lights in the examination room to improve image visualization (contrast resolution).

Lower Extremity

Select a 5–10 MHz linear array transducer for lower extremity scanning (Figure 17-5). Many ultrasound machines have settings that allow the clinician to adjust the frequency of the transducer. Higher frequency settings allow for better spatial resolution and improved viewing of more superficial structures, which maximizes image quality in thin patients. Alternatively, the lower frequency settings can optimize imaging in larger patients or deeper structures. Color Doppler and pulse wave Doppler may also aid in differentiation of arterial versus venous blood flow if the anatomy is difficult to identify. However, unlike the duplex ultrasound performed in most vascular laboratories, Doppler functions are used as an adjunct for identifying anatomy or assessing structures that cannot be compressed, and not as a primary modality in the limited compression ultrasound exam.

While venous compression is the most important method to evaluate the patency of veins in the lower extremity, some clinicians may choose to utilize color flow Doppler or spectral Doppler. Doppler techniques can be used to evaluate spontaneity, phasicity, direction, and augmentation of flow. In normal patent veins, flow is spontaneous and the velocity of flow varies (phasicity) with the changing intrathoracic pressures during the respiratory cycle. Typically, flow is anterograde and unidirectional unless there is venous valvular insufficiency. Additionally, venous flow can be augmented by applying pressure to the calf. Increase flow in the anterograde direction when performing this maneuver indicates patency of the vein. If an abnormality is noted using the Doppler adjuncts, have a heightened suspicion of venous thrombosis.

Place the patient in the supine position with the head of the bed raised 30–45° (Figure 17-6). This increases venous pooling in the lower extremities and distends the veins of the lower extremity. Extend the leg of interest and slightly externally rotate with the knee bent for the examination of the vessels in the proximal thigh (Figure 17-7). Obese patients may have an abdominal pannus that covers the proximal thigh and this should be raised. Usually, the patient can assist with this, but if unable, an assistant may be needed. Apply a liberal amount of ultrasound gel to the proximal thigh and place the ultrasound transducer on the thigh at the level of the inguinal crease.

Locate the femoral artery and vein and adjust the ultrasound transducer so that it is transverse to the long axis of the vessels (Figure 17-8). At the level of the inguinal crease, the common femoral vein is almost always medial to the artery, though this relationship can change as distance from the inguinal ligament increases. Visualize the junction of the common femoral vein and the greater saphenous vein because this is a common location for clot and the proximal starting point for the limited compression ultrasound of the leg veins (Figure 17-9A). Apply firm pressure to the transducer (Figure 17-10). Both the common femoral vein and the proximal portion the greater saphenous vein should be compressible (Figure 7-9B). Complete apposition of the walls of the vein excludes DVT. Adequate force must be applied to the ultrasound transducer to achieve complete compression. In the setting of DVT, the femoral artery can often be seen to compress and is an indication that adequate force has been applied. Novice clinicians may have difficulty fully compressing a normal femoral vein. This is most often due to either inadequate force of compression or compression at an angle oblique, rather than truly transverse, to the vessel.

Some experts think it is best to follow the common femoral vein distally and compress it every 2 cm until the bifurcation of the superficial and deep femoral veins (Figure 17-11) or 10 cm distal to the inguinal ligament if it is difficult to visualize the bifurcation. However, it may not be necessary to follow the vein distally because most studies are based on just one compression at the level of the inguinal ligament (Figure 17-9).2,3,11,23 Once examination of the common femoral vein is complete, proceed to evaluation of the popliteal vessels.

For evaluation of the popliteal vein, patient positioning is often more challenging (Figure 17-12). Gaining adequate access to the popliteal fossa is more difficult than the inguinal region in many patients, especially the obese. One common approach is to have the patient move to a lateral recumbent position with the examined leg in a dependent position and the knee slightly flexed. This position allows access to the popliteal fossa and optimal venous distention in the extremity.

The popliteal vein is located adjacent and superficial to the popliteal artery in the mid popliteal fossa (Figure 17-13A). Complete collapse of the vein lumen demonstrates patency of the vein and an absence of clot (Figure 17-13B). The popliteal fossa is a small area, and compression of the vein in more than one location can be quickly performed. We recommend compression of the proximal, mid, and distal popliteal fossa with the latter being identified as the popliteal vein reaches its trifurcation.

It is common to see smaller veins adjacent or superficial to the popliteal vessels and 5% of patients have a truly duplicated popliteal vein. Identification of the popliteal vein may be difficult in morbidly obese patients due to vessel depth and poor patient positioning. It is important to recognize that the popliteal vein, whether normal or duplicated, superficial or deep, is always accompanied by the popliteal artery. Additionally, the popliteal vein is the deepest vein in the popliteal fossa when viewed from a posterior approach, so visualization of the femur deep to the vessel is further confirmation that the vein in question is in fact the popliteal and not a more superficial vessel. If this is not appreciated, superficial veins may be mistaken for the popliteal vein and a DVT may be missed.

Controversy exists regarding the need to routinely scan the contralateral leg in patients undergoing limited compression ultrasound for unilateral lower extremity complaints. The incidence of contralateral, asymptomatic leg thrombi is as high as 34% in some patient populations, especially hospitalized patients and those with active malignancy or other significant risk factors for DVT.24 While some authors have argued that bilateral scanning should be the standard, others argue that scanning an asymptomatic extremity is not cost-effective and wastes resources.25–27 It may be reasonable to scan both extremities in very high-risk patients and only the symptomatic extremity in most outpatients.24 One study recommends a unilateral lower extremity scan in outpatients and a scan of the contralateral leg if the patient is found to have a DVT in the symptomatic extremity.28 Limited compression ultrasound is much faster compared to traditional vascular laboratory duplex scans, so the threshold for scanning both legs may be lower. However, in the setting of a busy ED, if only one lower extremity is symptomatic, scanning of the contralateral leg is generally not indicated.

Upper Extremity

Use a 5–10 MHz linear transducer for upper extremity vascular imaging. Place patients supine or in the Trendelenburg position, which increases neck and upper extremity venous engorgement, aiding in identification of anatomy and image acquisition. Begin the study by locating the distal portion of the internal jugular vein in the transverse plane (Figure 17-14). If there is difficulty locating the internal jugular vein, color Doppler may aid with identification. Apply gentle pressure with the transducer to completely collapse the vein in 1 cm increments while moving proximally. Minimize compression of the internal jugular vein only to that necessary to completely collapse the vein. Examine the internal jugular vein proximally to the point where it enters the brachiocephalic or subclavian vein. The proximal portion of the internal jugular vein becomes difficult to compress due to overlying bony structures; direct visualization of thrombus or color Doppler may be helpful in identifying any abnormality. The proximal subclavian vein can usually be visualized using a supraclavicular window with transducer orientation longitudinal to the vessel. It is not possible to compress the proximal subclavian vein so the exam relies on direct visualization of thrombus or visualization of color Doppler flow (Figure 17-15). It may be difficult to visualize the distal subclavian and proximal axillary veins but they should be compressed where possible. Resume a more direct examination when the distal axillary vein emerges in the axilla (Figure 17-16). Compress the brachial and basilic veins after they bifurcate from the axillary vein, moving distally to the level of the antecubital fossa. Compress these veins individually to ensure complete collapse. If there is a high suspicion of DVT in the axillary or subclavian veins and it cannot be visualized with ultrasound, then consider using CT to assist with the diagnosis.29

Documentation and Billing

Document diagnostic ultrasound examinations for the medical record and billing purposes. Documentation of the study should generally include:30

• Indication for the examination
• Views obtained
• Relevant findings
• Physician interpretation

Obtain and store images of the relevant anatomy. When billing for the study, at least one image of the study must be recorded and stored permanently to satisfy CPT coding criteria. Two-point limited compression ultrasound of the lower extremity for DVT is coded as a limited duplex scan of the lower extremity veins (CPT code 93971).31 Storing video clips of venous compression is the best way to document the study. If video is not available, split screen still images can be used to document vein compression (Figures 17-9 and 17-13).

The inability to fully compress the vein of interest with the ultrasound transducer indicates a thrombus within the vein. Normally, veins will compress easily while arteries can be difficult to compress. If pressure is inadequate or applied at an oblique angle, then the vein may not be fully compressed and a false positive interpretation may result.

Acute DVT

An acute DVT is best appreciated by the inability to completely compress the vein lumen (Figure 17-17). In general, an acute DVT is found centrally within the vein and may appear to be floating within the vein lumen (Figure 17-18). An acute DVT will also have smoother edges and be less echogenic than a chronic DVT, but the degree of echogenicity can be variable. Some acute DVTs may be echo lucent and can only be recognized by incomplete collapse of the vessel with compression (Figure 17-19). Occasionally, an obvious echogenic DVT will be noted within the vein prior to compression (Figure 17-20). Upper extremity clots may have a similar appearance (Figure 17-21). There have not been any reported iatrogenic complications, such as PE, from compression of a DVT during a limited compression ultrasound exam. False positive studies can result if echogenic appearance alone is used to make the diagnosis.

Chronic DVT

Chronic DVT refers to a condition where an acute DVT becomes recanalized over time, thus allowing venous blood to flow either through or around the thrombus. Prolonged presence of thrombus in the vein can cause damage to the venous valves resulting in venous hypertension, extremity swelling, erythema, and pain, which may mimic an acute DVT. A vein with a chronic DVT will not fully collapse, mimicking an acute DVT. In general, the thrombus of a chronic DVT is more echogenic and has a more ragged appearing edge than an acute DVT. Additionally, acute DVTs tend to recanalize centrally, leaving the thrombus of chronic DVT appearing to adhere to the walls of the vein (Figures 17-22 and 17-23). It is sometimes helpful to examine the vein in a sagittal view to differentiate acute versus chronic DVTs. Despite the differences between acute and chronic DVTs, both historically and in ultrasound appearance, it is important to remember that patients who have known chronic DVTs are more likely to develop acute DVTs within the same vessel. If there is uncertainty concerning chronicity, treat patients with positive ultrasound findings for acute DVT.

Superficial Venous Thrombosis

Providers will occasionally note thrombosis of a superficial vein when performing a limited compression ultrasound of an extremity. This most commonly occurs in the saphenous vein, but may occur in any superficial vein of the upper or lower extremity. Depending on the vein involved, a follow-up study in 5–7 days may be warranted to evaluate for extension of the thrombus into the deep venous system. Most treatment protocols do not recommend anticoagulation in the instance of superficial thrombosis. One notable exception is when a thrombosis of the proximal saphenous vein is either near to or “hanging” into the common femoral vein (Figure 17-24). In this situation anticoagulation is recommended. In other situations, such as thrombus in the antecubital or brachial veins, there are no clear treatment recommendations other than to obtain close follow-up and repeat the examination within 1 week (Figure 17-25).

When evaluating the lower extremity venous system, other rounded structures may be mistaken for normal and pathological findings. Lymph nodes may be encountered in the region of the common femoral vein, especially in ill patients (Figure 17-26). An inflamed lymph node can be initially mistaken for a noncollapsing vein due to similar echogenicity and cross-sectional structure. Careful sonographic evaluation in transverse and sagittal planes will show its true shape to be spherical rather than a tubular vessel. Duplication of the femoral or popliteal vessels can occur, and it is important to identify any extra vessels and ensure their patency as well. Deep veins are always accompanied by an artery, while superficial or “tributary” veins are not.

Findings in the popliteal fossa include Baker's cysts (Figure 17-27), which can be confusing when small in size (Figure 17-28). A Baker's cyst appears as a pocket of fluid with irregular borders that protrudes into the popliteal space and sometimes into the calf, and rarely, into the thigh. Careful examination of the structure should lead to its discrimination from the popliteal vessels. Consider rupture of a Baker's cyst in any patient with calf swelling who has a history of chronic arthritis or knee effusion. These can present with impressive swelling and pain and may present with fluid dissecting through soft tissue planes posterior to and below the knee on ultrasound (Figure 17-29). Popliteal artery aneurysms are occasionally encountered and may make it harder to compress the popliteal vein. Aneurysms larger than 2 cm can cause complications and should be followed closely.

1. Contraindication. There are no absolute contraindications for evaluating the deep venous system of the lower extremities. Patient comfort or level of cooperation may limit the examination. Consider administering analgesia prior to the exam to facilitate compression. There have not been any documented cases of embolization of a DVT due to a compression ultrasound examination.

2. Technically difficult exams. Patients who are morbidly obese or have severe lower extremity edema may be very difficult to image. The ultrasound beam greatly deteriorates with increased fat as well as distance. A variety of adjustments or changes can be made on some equipment to optimize image quality. Options include tissue harmonics, spatial compounding, and other image processing features. Using a lower frequency transducer is also an option. In a large thigh, make sure the vessel of interest is positioned directly between the transducer and femur, otherwise it will be difficult to achieve complete compression.

3. Segmental DVT. One concern about the limited compression ultrasound examination is the possibility of segmental DVT; for instance, a DVT potentially may span several centimeters of the superficial femoral vein mid-thigh but cannot be found elsewhere. The true incidence of such an occurrence is not known, but evidence suggests that it is very rare. However, a repeat study in 5–7 days is often recommended after a negative limited compression ultrasound exam. This will detect propagation of an undetected calf thrombosis and a segmental clot. If a patient is able to identify a specific area of localized pain or swelling on his or her thigh, evaluating that area for possible DVT is reasonable and may be reassuring.

4. Misunderstanding the limitations of ultrasonography. Although ultrasound is now the method of choice for detecting the presence of lower extremity thrombosis, it is not 100% accurate. Practitioners should understand the limitation of ultrasound, especially when considering that the method described in this chapter does not attempt to evaluate veins in the calf. Furthermore, the use of ultrasound examination of bilateral lower extremities to exclude PE is fraught with potential danger if the physician does not keep in mind that only a positive finding is helpful. Many patients with PE will not have a proximal DVT found on lower extremity ultrasound. This may be due to a nonlower extremity source or due to the thrombus completely embolizing to the lungs.32

5. Mistaking artery for vein. While this is not a common pitfall, novice operators should be aware that in some cases an artery may be pliable enough to collapse under moderate transducer pressure, while the vein lumen is held open by the presence of clot. If available, color and pulse wave Doppler may help simplify the identification of blood vessels.

6. Femoral lymph nodes mistaken for a DVT. Occasionally, lymph nodes encountered in the groin can be mistaken for a noncompressible deep vein. This is especially true for inflamed lymph nodes. Figure 17-30 shows an example of a large lymph node that was mistaken for a femoral DVT. The lymph node is an oval-shaped structure, and moving the transducer proximally or distally will allow the clinician to identify the edges of the lymph node. Rotating the transducer will also frequently show the boundaries of the lymph node as well as its atypical appearance for a blood vessel. Lymph nodes tend to be more superficial or closer to the skin surface than deep vessels.

7. Pelvic vein thrombosis. Thrombosis of the pelvic veins, such as the external iliac, frequently occurs in combination with DVT of the common femoral and more distal venous segments. Thus, identification of clot in the external iliac vein is not as crucial when a common femoral DVT is located and the patient is anticoagulated. However, in a small percentage of cases, thrombosis of the pelvic veins is an isolated event.33 Isolated pelvic vein thrombosis may be quite challenging to diagnose and poses a high risk of embolization. Ultrasound interrogation of the external iliac, common iliac, and the proximal portion of the internal iliac vein is possible in few thin patients without interfering bowel gas. In a minority of patients, the external and common iliac can be seen and compressed. If suspicion for pelvic vein thrombosis exists and ultrasound will not provide adequate imaging, then other diagnostic measures such as CT with venous angiography will have to be employed. Even if the iliac veins cannot be visualized, a DVT may be suspected if there is a lack of respiratory variation in the venous flow in the common iliac vein. Normally, variation is seen in the baseline venous flow with respiration (Figure 17-31). If this variation is absent, it is suggestive of a proximal obstruction, such as a thrombus in the external or common iliac ipsilaterally. Conversely, if respiratory variation is observed, then there is unlikely to be a complete obstruction of proximal vein.

8. Slow venous blood flow. Occasionally, blood flow in a vein segment may be slow enough that swirling of the blood is actually seen within the lumen. This can have the appearance of echogenic material in the vein and be mistaken for a thrombus. It is important not to make this mistake by moving too quickly through the examination. Compression of the vein segment will reveal complete collapse of the vein and disappearance of the vein lumen.

9. Mistaking the saphenous vein for the superficial femoral (deep) vein. The saphenous vein runs superficially down the anterior and medial thigh after its takeoff from the common femoral vein. Its most prominent feature is the absence of a paired artery. If an examiner mistakes this vessel for the superficial femoral vein, a DVT in the femoral vein may be missed.

10. Limited compression sonography for DVT. There is a risk for abbreviating this exam too much. A limited exam is not exclusive of a thorough exam. Preparation of the patient and equipment is likely to take more time than the actual ultrasound examination. The ultrasound imaging is limited to two main areas in the lower extremity, but several compression segments of each area are recommended (see section ‘Technique and Normal Ultrasound Findings’). Early thrombus formation is often associated with branching areas of the vein, so the clinician should also attempt to visualize and compress the confluence of these main branching areas (Figure 17-32).

Case 1

Patient Presentation

A 25-year-old woman presented to the ED with a complaint of right calf swelling and pain. The patient was a law school student who was studying for final examinations. She denied any strenuous activity and noted spending most of the last week sitting in the library. The patient was normally athletic and rides a stationary bicycle daily. She had an unremarkable medical history and did not smoke. She thought her older sister had a “blood clot” several years ago.

Physical examination revealed a healthy young woman with normal vital signs, including an oxygen saturation of 98% on room air. She had a moderately tender right calf without any visible erythema or palpable cord. The patient had moderate discomfort on manipulation of her foot at the ankle. Her right calf measured approximately 2.5 cm larger than the left, a fact the patient attributed to a left knee injury while playing soccer in college.

Management Course

The vascular laboratory was not open on Saturday. Previous department policy suggested anticoagulation until ultrasound was available on Monday, but the emergency physicians had recently become credentialed in limited compression ultrasonography. The emergency physician performed an ultrasound examination of the patient's right leg. The common femoral and saphenous vein junction and the deep femoral and superficial femoral veins were located. All were noncompressible. The popliteal vein was visualized behind the knee and also did not compress. Because of the extensive nature of her DVT, a vascular surgeon was consulted for consideration of thrombolytics and/or mechanical clot retrieval. The patient was eventually discharged on low molecular weight heparin injections. A follow-up appointment with a vascular surgeon was made for the following week.

Commentary

Case 1 represents an example of a fairly low-risk patient who can still inspire considerable angst for the treating physician. With her suggestive symptoms and family history, the patient might present a medicolegal risk if she was discharged home without definitive diagnostic imaging and had a complication from anticoagulation that was later determined to be unnecessary. Treating the patient presumptively with low molecular weight heparin as an outpatient may seem attractive, but it has some limitations. The patient must be taught how to administer the injections. Also, there was a risk of bleeding even if it was relatively low. Discovering the extent of her clot changed the management from simple anticoagulation to consideration of more aggressive therapy. With increasing concerns about post-thrombotic syndrome in patients treated with anticoagulation alone, and with recognition that thrombolysis and/or mechanical clot retrieval may both reduce the risk of post-thrombotic syndrome and return patients to full function sooner, it is prudent to consider these treatment modalities in facilities where such expertise is available.34

This scenario is quite realistic in many facilities. Staffing a vascular laboratory 24 hours a day, 7 days a week, can be very expensive, especially when coupled with a shortage of sonographers. In this case, the emergency physician was able to confidently demonstrate an extensive DVT, justify the risk of anticoagulant treatment, and seek an appropriate consultation.

Case 2

Patient Presentation

A 32-year-old woman with no previous medical history presented to the ED with dizziness and dyspnea. She reported her last normal menstrual period to be 7 weeks ago. On physical examination, her blood pressure was 70/50 mm Hg, heart rate of 135 beats per minute, and respirations 26 per minute. She was a diaphoretic young woman, pale, and in moderate distress. Her examination was otherwise unremarkable, including nontender, nonedematous legs.

Management Course

Her point-of-care pregnancy test was negative. The emergency physician performed bilateral lower extremity ultrasound exams, which showed a DVT in the left popliteal vein. Despite anticoagulation and fluid resuscitation, the patient's vital signs continued to rapidly deteriorate, so a systemic thrombolytic agent was administered for her presumed PE. The patient's clinical status gradually improved in the ICU.

Commentary

Emergent management of critically ill patients with known or suspected PE goes beyond anticoagulation and includes systemic thrombolysis, local catheter directed thrombolysis, or mechanical thrombectomy.35 Case 2 illustrates the benefit of critical information in time-sensitive situations, especially when therapies have risk (anticoagulation, thrombolysis) or require significant and rapid coordination of care (emergent interventional radiology consult). Delaying these interventions for an ultrasound examination by the vascular lab or diagnostic imaging service presents significant increased risk to the patient.

Case 3

Patient Presentation

A 22-year-old woman with a history of sickle cell disease presented with a complaint of left lower leg swelling and pain. The patient stated that she first began to notice discomfort in the leg 4 days ago and today noticed swelling, redness, and increased pain. She denied any history of trauma and stated that her typical sickle cell pain is higher in the leg and that this pain has a different quality.

Physical examination revealed normal vital signs with a temperature of 100.0°F. The examination was within normal limits except for the patient's lower left leg. She had erythema and increased temperature of the anterior shin as well as nonpitting edema. The area was sensitive to the touch. The calf was mildly tender and slightly swollen. The patient's ankle was also swollen but no deformity was noted. She had diffuse pain in the ankle and anterior shin with flexion and extension of the foot. Distal pulses were present and equal to the contralateral side.

Management Course

A point-of-care ultrasound examination of the left leg was performed using the diagnostic algorithm in Figure 17-2 for clinician-performed ultrasound. The femoral and popliteal veins were completely compressible. The patient had planned on traveling next week and wished to avoid a repeat study. A D-dimer assay was positive, and the patient was counseled about the importance of returning in 5–7 days for a repeat study. A diagnosis of cellulitis was made with the patient being discharged home on oral antibiotics. She did follow up 1 week later and the repeat ultrasound exam was also negative.

Commentary

The primary goal of point-of-care ultrasound is to rapidly provide quality clinical information to assist in clinical decision making. Because of concerns about patient follow-up, the physician sent a D-dimer assay instead of just scheduling a repeat ultrasound in 1 week. Because the D-dimer assay was positive, the patient was instructed about the importance of the follow-up study. Alternatively, if the physician used the algorithm in Figure 17-1, the patient would be at low risk per the Wells criteria (Table 17-2), but the positive D-dimer assay would have led to the limited compression ultrasound in the ED, and subsequently the follow-up ultrasound exam in 5–7 days with the identical outcome.