Chapter 15. Deep Venous Thrombosis

In recent years, medicine has seen the spread of bedside ultrasonography beyond the traditional scope of practice employed by early emergency sonologists.1–4 Many of the new applications adopted by emergency sonologists have resulted from a clinical need to improve efficiency of patient care. One such application has been ultrasonography for the detection of deep venous thrombosis (DVT).5, 6 This typically refers to lower extremity DVT, although the frequency of upper extremity DVTs encountered appears to be increasing.7

Approximately 260,000 cases of lower extremity DVT are diagnosed each year in the United States.8 These, in turn, are thought to lead to as many as 50,000 deaths per year due to pulmonary embolism.8 To avoid the potentially fatal sequelae of DVT, physicians in the United States order almost 500,000 lower extremity duplex ultrasound examinations per year.9 Many vascular ultrasound laboratories find it difficult to maintain 24-hour coverage, 7 days per week, for emergency evaluation.10 This has resulted largely from lack of funding and trained personnel. Many hospitals now have an absence of vascular laboratory services during off-hours. The result is that the emergency or primary care physician is compelled to empirically treat and often admit patients who may have a DVT.

Overcrowding in emergency departments has stretched resources to the breaking point, resulting in delays in obtaining a host of services for emergency department patients. Moreover, even though extremity ultrasonography may be available at a facility, it may take hours to obtain a result, thus delaying the patient in the emergency department unnecessarily. Emergency physicians choosing to perform ultrasound examinations of the lower extremity themselves have been shown to decrease the time to patient disposition by over 2 hours.11

The high incidence and considerable morbidity and mortality resulting from DVT, coupled with the potential difficulty encountered in trying to diagnose it, has made this a disease of significant importance.12 The use of low-molecular-weight heparin makes it possible to send some patients home without obtaining a diagnostic study. The patient can then undergo an outpatient study the following day, which, if negative, would lead to termination of anticoagulation therapy.13, 14 However, there are some drawbacks to this strategy. Patients who are sent home require training in self-administration of low-molecular-weight heparin. This may be difficult to accomplish in a busy emergency department or outpatient setting. Furthermore, despite the relatively low incidence of bleeding with low-molecular-weight heparin, complications are occasionally encountered and can be severe. Another reality is that many primary care physicians still elect to admit their patients with actual or suspected DVT. Lastly, although rare, a fresh DVT can resolve rapidly with anticoagulation and it is possible that an ultrasound obtained 24 hour later may not demonstrate a DVT since it has already resolved—perhaps temporarily. This is a disservice to the patient who may not undergo a full evaluation for DVT or is at risk for recurrence.

It is not surprising that physicians have long sought a means of more accurately diagnosing or excluding DVT at the bedside. This is reflected by the many clinical decision rules that have been developed and the attempts made to integrate d-dimer assays into DVT evaluation.15, 16 The adoption of prediction rules has improved efficiency in choosing which patients are at a real risk for having a DVT. By excluding low-risk patients, those who would have required an ultrasound in the past can now be sent home without an imaging study. However, not all patients suspected for DVT are low risk and some will require evaluation by ultrasound.

Emergency ultrasound can within minutes diagnose or exclude DVT. With such rapid diagnosis available at the bedside, ultrasound examinations can be utilized routinely for diagnosis. In addition, physicians can perform follow-up examinations when patients are unable to obtain them as indicated. Although this is not ideal for treatment of DVT, it could reduce the frequency of patients lost to follow-up due to financial limitations or noncompliance.17

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

• Suspicion of lower extremity DVT
• Suspicion of upper extremity DVT

Lower Extremity DVT

An examination of the deep veins of the lower extremity is indicated whenever a proximal DVT is suspected. Proximal DVT is loosely defined as a clot or thrombus in the popliteal vein or higher in the leg. Its significance is that it is associated with a greater risk of embolization than a calf vein DVT.18

The complete duplex ultrasound examination performed by imaging specialists is somewhat lengthy, with one leg taking up to 37 minutes in one study.19 In addition, it may or may not include an evaluation of the veins below the trifurcation of the popliteal vein distal to the knee. The complete study involves a slow, painstaking evaluation of each vein roughly one-probe width at a time. Each small segment of vein is visualized and checked for complete collapse under pressure from the transducer. Multiple blood flow measurements are taken using color and pulse wave Doppler. A difficult examination of the entire leg can take as much as an hour in some vascular laboratories. The main culprit for this extended period of time is the calf and its veins.

Several studies have shown that the traditional complete examination may not be necessary. An abbreviated approach may maintain high accuracy and patient safety while decreasing the time required for an examination. The abbreviated approach argues for spot checks of vein compressibility, usually at the junction of the common femoral, deep femoral, and superficial femoral veins and the popliteal vein. This allows for considerable time savings and increases patient comfort, and there is considerable evidence that this method is safe and effective.

One study evaluated 204 consecutive patients who had undergone elective, major lower extremity surgery.20 These patients were part of a general screening for lower extremity DVT and were not specifically referred for testing. The investigators found that simply compressing the vein to assess its patency produced a sensitivity of 60% and a specificity of 96%. The addition of color Doppler did not improve the study results. In these patients, venous compression was performed over the entire leg, a time-consuming task. Perhaps the most important point here is that color Doppler did little to improve detection of proximal DVT.

In 1989, a group of investigators published their findings on a head-to-head comparison of contrast venography with B-mode ultrasonography in 220 consecutive patients.21 The only criterion used to detect DVT with ultrasound was lack of compression in either the common femoral or popliteal veins. For proximal vein thrombosis, the study yielded a sensitivity of 100%. When patients with calf vein thrombi (located on venogram) were included, the sensitivity and specificity were 91% and 99%, respectively. The study showed that in comparison to the gold standard this simple method of DVT detection was highly accurate.

A number of other studies also confirmed high sensitivity and specificity for the detection of proximal lower extremity DVT without the utilization of color Doppler.8, 9, 19, 20 The studies noted considerable time savings when segmental checks were performed, which raised the question for the necessity of compressing every inch of vein in the proximal venous system. Proponents for compressing every inch of vein in the proximal venous system point out the potential for occurrence of segmental DVTs. These are venous thrombi that are limited to only one section of the deep venous system. For example, the popliteal vein may be without thrombus as well as most of the superficial femoral vein; however, a 3-inch section of the superficial femoral vein in the mid-thigh could contain thrombus. One study examined the incidence of a small isolated thrombus segment, such as in the iliac and popliteal veins, and found an incidence of 0 out of 195 legs studied.22 Thus, the chance of missing evidence of segmental thrombi is minimal. Another study prospectively analyzed 72 patients for DVT using an abbreviated technique with only two compression sites per leg.19 The two sites used were the saphenofemoral junction and the lower popliteal vein. For proximal DVT, the sensitivity and specificity of simple compression in these two sites were 100% and 98%, respectively. The authors addressed potential criticism of their abbreviated technique by noting that in a study of 491 patients found to be without DVT by compression ultrasonography, only 1.5% had a proximal DVT during the 6-month follow-up evaluation.23

In 1996, a study of 721 patients, on whom 755 examinations were performed, examined the safety of abbreviated studies for DVT.24 All patients were referred to a vascular laboratory for suspicion of DVT. A complete examination was performed on each patient and the authors attempted to make retrospective inferences from the results. They concluded that DVT limited to a single vein occurs with enough frequency that the ultrasound survey for thrombosis should not be limited. However, the investigators failed to note that even the isolated thrombus segments in their study were within the area interrogated by the abbreviated approach and would have been detected.

In 1998, a large study evaluated the abbreviated compression approach in 405 consecutive outpatients suspected of having a first-time lower extremity DVT.9 Each patient had his or her common femoral and popliteal veins assessed for compressibility. In those with normal results, testing was repeated in 5–7 days. Regardless of symptoms, patients with negative results on compression ultrasound did not receive anticoagulation. Follow-up was performed on all patients at 3 months after the initial negative study. Of the patients studied, 63 had DVT detected on initial ultrasound examination. Repeat ultrasound studies picked up 7 proximal DVTs that were not present on initial examination and may have propagated proximally from veins in the calf. None of the patients with normal results died of pulmonary embolism during the follow-up period.

The patency of lower extremity veins should be checked in any patient in whom a clinician suspects of having a lower extremity DVT. Patients with symptoms suggestive of DVT typically have calf swelling and pain posteriorly.25 Redness of the posterior calf can also be suggestive. Although a number of studies have suggested that DVT is unlikely to be present without a minimum of a 2-cm difference in calf diameter between the affected and contralateral sides, in practice this is not always the case.26 Debilitated patients or ones who are unable to communicate may require a lower threshold to image because of their inability to relate common symptoms of DVT.

The risk factors commonly described for the development of DVT include smoking, abdominal surgery, lower extremity injury, venous stasis, previous history of DVT, and congestive heart failure, among others.27–29 Thus, any person who has a risk factor and presents with calf pain and swelling is a candidate for undergoing a study to exclude DVT. Despite a number of studies that have suggested at least several risk factors must be present to warrant emergency evaluation for DVT, many physicians may feel obligated to exclude the presence of the disease for marginal indications.27–29

Bedside emergency ultrasound examination of lower extremity veins is of greatest use in facilities that lack vascular laboratory access at night or on weekends. Emergency or primary physicians often find themselves having to empirically treat patients they suspect of having a DVT. This typically involves either admission for heparin therapy or outpatient treatment with low-molecular-weight heparin therapy. The latter can be made difficult if expeditious follow-up cannot be arranged or if the local medical culture frowns on outpatient treatment of uncomplicated DVTs. The high accuracy that can be achieved with a modified lower extremity duplex will allow discharge without anticoagulant therapy for those patients found to have a negative study. It is imperative to keep in mind that moderate- and high-risk patients who require a lower extremity ultrasound to exclude a DVT should have a repeat scan in 5 to 7 days. This will allow for diagnosis of DVT if a distal thrombus (one in the calf itself) progresses proximally. This is expected to occur in not more than 20% of distal DVT cases.9

In general, bedside emergency ultrasonography is not recommended for diagnosing DVTs limited to the calf or ankle. Success rates can be as low as 40% even for experienced vascular technologists; if complicated by edema or large body habitus, success rates will be even lower.30 Many vascular laboratories no longer scan below the calf and prefer to reexamine patients or perform venography if high suspicion of a calf DVT exists.

Upper Extremity DVT

Prior to the 1970s, upper extremity DVT was thought to account for less than 2% of all DVT cases.31 Since that time, some studies have shown upper extremity DVTs to make up as much as 18% of all DVTs and 0.18% of adult hospital admissions.32 The most common causes of this disease process include malignancy, central venous access lines, and pacemaker wires. Studies have demonstrated that as many as 7 to 9% of upper extremity DVTs will lead to an acute pulmonary embolism.33, 34

While the gold standard test of venous compression works well in the lower extremities, the subclavian vein does not lend itself to easy compression. Excluding upper extremity DVT depends on indirect confirmation of vein patency in a major venous segment. Although not well studied, this suggests that ruling out an upper extremity DVT may be more difficult for the novice sonologist than in the lower extremities. The solution for some sonologists has been to rely on positive findings for an upper extremity DVT, but not on their negative findings. Patients who have a negative ultrasound examination may be referred to vascular laboratories or radiology for a formal examination. Essentially, since most sonologists are familiar with the appearance of thrombosed deep and peripheral veins, diagnosis of an upper extremity DVT will be highly reliable.

The venous system of the lower extremity is quite simple in a proximal to distal examination until the calf is reached. Although many clinicians may feel they have a “sixth sense” for the location of the femoral vein and artery after several years of practice and the placement of numerous central lines, few clinicians are truly aware of the variations that can exist even at that level of the thigh. While physicians are taught that the femoral vein is located just medial to the pulse from the femoral artery, the novice sonographer quickly discovers that vein and artery may often lie on top of one another rather than side by side. When this happens, a 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 common femoral vein then diverges into the deep femoral and superficial femoral veins (Figure 15-1). The nomenclature used here is deceptive and there have even been efforts to change the name of the superficial femoral vein as inexperienced clinicians have sometimes mistaken reports of thrombus in the superficial femoral vein as being outside of the deep venous system. The deep femoral vein travels deep into the thigh. The superficial femoral vein proceeds distally until it dives into the obturator canal. In this region, the vein is difficult to access until it emerges behind the knee as the popliteal vein.

The upper extremity deep veins include the radial and ulnar veins, which arise from the palmar venous plexus (Figure 15-2). 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, on either side of the brachial artery, and flows into the axillary vein approximately where it is joined by the basilic vein (superficial). The axillary vein flows into the thorax, changing into the subclavian vein. The subclavian vein is then joined by the internal jugular vein to form the brachiocephalic vein.

The ultrasound machine is traditionally parked on the right side of the patient. It should be turned on and allowed to boot up. Most modern ultrasound machines will have specific settings that will optimize image processing for a lower extremity venous examination. Once these settings are selected, a linear transducer should be selected in the case of a multitransducer machine. In a machine with a single attached transducer, the linear one should be attached and activated. When possible, the lights in the examination area should be dimmed enough to optimize image visualization on the ultrasound screen while still being able to see transducer placement on the patient. In this chapter, linear probe or transducer refers to a transducer with a linear scanning format and one that is a linear array.

Lower Extremity

To perform a lower extremity venous ultrasound examination, a high-resolution linear transducer is required. Most modern ultrasound systems found in emergency departments and clinician offices will have this capability. Color Doppler can be helpful, especially if vascular structures are difficult to distinguish because of poor visualization through soft tissue. Power Doppler, a more sensitive but nondirectional version of color Doppler, can be used as well and is even more likely to detect very slow blood flow, such as in veins.

Ideally, a patient is positioned as needed to maximally distend the leg veins. Many full-length protocols include having the patient dangle his or her leg over the edge of a bed or table (Figure 15-3). This kind of manipulation is not realistic for many clinicians, especially when dealing with acutely ill patients. That said, distended veins do make better targets and it is best to have the head of the patient's bed up at least 30°, with 45° being preferable. This allows for blood to pool in the lower extremities and may make evaluation of the vein in question much easier. Alternatively, the bed can be put into reverse Trendelenburg position to have venous blood pool in the lower extremities (Figure 15-4). Vascular laboratories occasionally apply a tourniquet to the extremity to optimize vein engorgement.

An ultrasound transducer with appropriate resolution should be used. Thin patients may require a 7.5 to 10 MHz transducer while larger patients may need the increased penetration of a 5 MHz probe. All of these frequencies can often be obtained in a single broadband transducer. A probe should be utilized that will allow for adequate compression of underlying vascular structures (Figure 15-5). Transducers with a curved face can make it more difficult to achieve adequate compression of soft tissue to ensure collapse of a patent's vein or veins. If challenged by lack of adequate equipment, enterprising physicians can make due with a wide range of transducers, even an endovaginal probe, although the compression achieved may be poor.

The patient's leg may be bent at the knee and turned outward (Figure 15-6). This allows for greater access to the femoral vessels in the proximal thigh and the popliteal vein. However, too great a bend at the knee may actually hinder image acquisition by introducing additional soft tissue and skin between the transducer and vein. The proximal inner thigh and popliteal fossa should be well exposed. The femoral vein and artery are easiest to find with the transducer placed transverse to the long axis of the vessels (Figure 15-7).

An adequate amount of ultrasound gel should be placed on the area of skin where the transducer will be located. The examination starts as proximally as possible in the inguinal area; generally at this location the common femoral vein and artery are visualized in cross section. Ideally, the transducer should already be above the junction of the common femoral and saphenous veins, but positioning may need to be adjusted more proximally. In some patients the pannus may need to be moved or lifted to expose the most proximal site. Firm pressure downward should be applied to the transducer at the junction of the saphenous and common femoral veins. Both veins should be observed to collapse, thus ensuring patency. The transducer is then moved distally approximately 1 cm at a time and compression repeated. The examination proceeds through the junction of common femoral, superficial femoral, and deep femoral veins. At each point, firm compression should be applied to achieve collapse of the vein (Figure 15-8). Although for purposes of demonstrating probe location, the sonologists here appear to be holding the transducer far from the scanning tip, actually doing this would make the scan difficult. The transducer is held close to the scanning tip and a portion of the hand should touch the patient's skin to help anchor the transducer and keep it from sliding on the skin (Figure 15-9). In general, enough downward pressure has been applied when the artery is seen to deform. However, stiff venous walls that are resistant to compression in some patients can complicate this. The normal vein should collapse easily while the artery should remain largely intact (Figure 15-10). If there is any difficulty distinguishing artery from vein, color Doppler may be helpful. While both vein and artery may show color flow, the flow in the artery will usually appear more pulsatile than in the vein. The pulse repetition frequency (PRF) can be adjusted (increased) so that slower, and presumably venous, flow will not be picked up. The most reliable method to differentiate venous from arterial flow would be to activate pulse wave Doppler and compare waveforms between the vessels. The waveform seen in veins will tend to be continuous, with flow still noted in diastole. Arterial waveforms should have a peak and trough quality or a frank triphasic flow pattern. The deep femoral vein is often difficult to follow for more than 1 or 2 cm, but it is critical to ensure complete compression of the proximal segment as it drains into the common femoral vein (Figure 15-11). The total length of the upper leg segment scanned and sequentially compressed (includes the common femoral, saphenous, superficial, and deep femoral veins) is usually not more than 2 or 3 inches in length.

After ensuring patency of the common femoral, proximal great saphenous, common femoral, and deep femoral veins, the simplified approach calls for continuing on to the popliteal fossa. The proximal portion of the popliteal vein is found high in the popliteal fossa. The probe is placed behind the knee and the popliteal artery and vein are located (Figure 15-12). Again, firm pressure is applied to collapse popliteal vein. Applying counterpressure with the nonscanning hand on the outside of the knee may facilitate compression of the popliteal vein. The popliteal vein is traced down to its trifurcation, with compression and relaxation over every centimeter. The distance covered is usually less than 5 cm. It is useful to compress and ensure collapse of the very proximal portions of the calf veins just after trifurcation of the popliteal vein. A clot located in a proximal calf vein can easily extend in the popliteal and seed a proximal DVT. These patients should be treated as a typical proximal DVT. Duplication of the popliteal vein is possible and, if present, both should collapse completely. Complete collapse of the vein's lumen should be visualized, as described above for the femoral veins. Partial collapse can indicate the presence of a clot in the vein; however, poor collapse of the lumen may also be caused by inadequate compression of the vein. This can be improved by transducer adjustment or patient manipulation.

Opinions vary on whether or not the contralateral leg should be scanned on a routine basis. Two studies that looked at a combined 3202 patients concluded that in patients with unilateral leg symptoms scanning the contralateral leg was neither indicated nor cost-effective.35, 36 Others have argued that bilateral DVTs are not uncommon and scanning the contralateral leg is indicated.37 However, this view fails to account for the fact that treatment of unilateral DVT is usually identical to treatment of bilateral DVT. Novice sonologists may find it helpful to compare the anatomy of the contralateral leg when it appears confusing on the extremity being investigated. Otherwise, routinely scanning the asymptomatic leg appears to be unnecessary.

When a DVT is diagnosed, locating the most proximal end of the thrombus may be helpful. Hence, if examination of the femoral vein is normal, but a DVT is found in the popliteal fossa, an effort should be made to track the clot proximally. Identifying the proximal end of the thrombus and noting it in the patient's chart may facilitate patient follow-up, especially if a repeat examination after anticoagulation identifies continued presence of thrombus. Longitudinal views of the vein may be helpful in outlining the shape and extent of the thrombus. Comparison with the position of the proximal end of the thrombus at the time of diagnosis will allow the treating physician to decide if therapy is failing and disease progression has occurred; this may result in more invasive interventions to safeguard the patient from embolization.

Documenting the results of the examination is required if formal reports are being issued. Still images have traditionally been used although physicians are also beginning to utilize video clips. When documenting still images in the medical record, a split screen feature is quite useful. The split screen allows the sonologist to show two images on the screen, with the view on the left being without compression and the one on the right with compression (Figure 15-13). Three standard thermal prints can be attached on one half of an 8.5 × 11 sheet of paper containing the written report on the other half of the same side. With split screen printouts, the sonologist can illustrate whether or not compression at the common femoral and saphenous junction resulted in vein collapse. The next split screen image can address vein lumen response of the proximal superficial femoral and deep femoral veins. The third and final one can show the response of the popliteal vein.

Upper Extremity

The patient should ideally be examined in the supine position to maximize venous distention. Sonologist preference varies for starting points. Some start at the internal jugular, as superior as possible (Figure 15-14). The jugular vein is located in cross section and lightly compressed. The carotid artery can be differentiated from the jugular vein based on pulse waveforms if the anatomy is not obvious. Gentle compression approximately every centimeter is employed as the jugular vein is traced proximally. Aggressive compression should be avoided in elderly persons. Furthermore, simply elevating the patient's torso will make many jugular veins disappear without any compression.

The jugular vein can typically be visualized entering the brachiocephalic vein with the subclavian vein. Compression at this point is not possible and direct visualization of thrombus or lack of flow on color or power Doppler will be the best method for sonologists to diagnose a DVT. The subclavian vein is then traced toward the shoulder with Doppler interrogation wherever it is visible (Figure 15-15). Pulsed wave Doppler can differentiate between the subclavian artery and vein, if the anatomy is not obvious. The proximal portion of the axillary vein usually cannot be visualized because of overlying bone. Once in the axilla the axillary vein and the brachial vein can again be directly compressed to assure patency (Figure 15-16). Once the antecubital fossa has been reached the radial and ulnar veins split to either side of the forearm and are compressed one at a time.

The inability to collapse a vein on ultrasound indicates the presence of thrombus within the vein (Figure 15-17). The same does not apply to arteries, which can be difficult to collapse. It is imperative to recognize that one must have adequate access to the vein to test collapsibility. Applying pressure at an angle or in an area where overlying structures may distribute pressure away from the vessel lumen might result in false-positive findings.

Acute DVT

The clot itself may be seen as an echogenicity within the lumen, and the vein will not collapse completely with compression (Figure 15-18). Longitudinal views of a vein may be helpful in outlining the shape and extent of thrombus (Figure 15-19). In many instances, especially with more primitive equipment, the only evidence of a DVT is the inability to compress the vein. Near complete compression of the vein is not sufficient to exclude DVT (Figure 15-17). The lumen of the vessel must disappear completely to exclude the presence of a clot (Figure 15-10). An obvious thrombus that appears to be free floating, or not attached to the vessel walls, should not be unnecessarily compressed if the diagnosis is obvious (Figures 15-20 and 15-21). In such cases a longitudinal image of a floating clot will adequately relay the diagnosis (Figure 15-22). While there have not been any reported cases of embolization caused by ultrasound evaluation, it is simply not necessary to compress an obvious floating thrombus. In addition, a floating thrombus has the highest chance of embolization.

Chronic DVT

This condition refers to the presence of an old clot within a vein that has recanulated and allowed venous flow around or through the clot. Complete collapse of the venous lumen will not be possible. Acute DVT may have a similar appearance and occlude only part of the vein. Acute clots tend to be less echogenic than chronic ones; however, this is not always reliable (Figure 15-23). Clots tend to recanalize centrally and may thus leave a channel of blood flow through the central area of the thrombus (Figure 15-24). Despite the fact that there may be historical indications that a clot is chronic, as well as echogenicity differences between acute and chronic clot, it may still be difficult to differentiate between the two in a newly diagnosed patient. Review of prior ultrasound studies is helpful when available. Interrogating the vein in long axis can also be helpful. The sonologist may be able to visualize thickened vessel walls resulting from scaring of the previous thrombus. This appearance differs from acute DVT enough to allow differentiation and correct diagnosis (Figure 15-25). The chronic thrombus will tend to be more irregular and will compress less. Collaterals are more likely to be present with a chronic DVT and should be sought. If the diagnosis remains uncertain at this point, it may be prudent to treat the patient for an acute DVT, with a formal ultrasound examination performed within 24 hours. This situation is infrequent, and the history and ultrasound examination will lead to a diagnosis in the majority of possible chronic DVT cases.

Superficial Venous Clot

The physician evaluating the source of focal leg pain and swelling may encounter a superficial venous clot. It is not uncommon to find a clot limited to the saphenous vein when investigating DVT in the thigh. Although recommendations for treatment of superficial clot, such as in the saphenous vein, differ from source to source, superficial venous thrombosis clearly does not pose the same degree of danger in most patients unless it is propagating into the saphenofemoral junction. Clot in the saphenous vein, near the entrance to the common femoral vein, should be considered a DVT since propagation and seeding of the common femoral vein is not unlikely. Similarly, superficial thrombi that have progressive symptoms may need to be reassessed to detect clot propagation (Figure 15-26). Findings of a propagating superficial thrombus may lead some clinicians to anticoagulate the patient or at least require close follow-up.

When evaluating the lower extremity venous system, other cystic structures may be mistaken for normal and pathological findings. Lymph nodes may be encountered while studying the common femoral and femoral vein junction, especially in ill patients (Figure 15-27). An inflamed lymph node can be initially mistaken for a noncollapsing vein due to similar echogenicity and cross-sectional structure. Careful ultrasonographic evaluation of the structure will show its true shape to be spherical rather than a tubular vessel. Duplication of vessels can occur, and it is important to identify any extra vessels and ensure their patency as well.

Findings in the popliteal fossa include Baker's cysts (Figure 15-28), which can be confusing when small in size (Figure 15-29). Careful examination of the structure should lead to its discrimination from the popliteal vein. Rupture of a Baker's cyst should be considered 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 reveal fluid, dissecting through soft tissue planes, posterior to and below the knee on ultrasound (Figure 15-30). Popliteal artery aneurysms are occasionally encountered and may make it harder to compress the popliteal vein in one location. Aneurysms over 2 cm can cause complications and should be followed closely.

1. Contraindication. There are no absolute contraindications to evaluating the deep venous system of the lower extremities. Patient comfort or level of cooperation may limit the examination. There have not been any documented cases of embolization as a result of DVT evaluation in a patient. An obvious free-floating clot, however, does not require compression.

2. Imaging challenging subjects. 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 imaging and the sonologist should be aware of what these are on the machine. Such helpful functions can include tissue harmonics, compound imaging, and other software or hardware functions.

3. Segmental DVT. One concern about this examination is the possibility of segmental DVT; for instance, a DVT potentially may span several centimeters of the femoral vein midthigh but cannot be found anywhere else. The true incidence of such an occurrence is not known, but evidence suggests that it is very rare. However, as is recommended for all moderate- and high-risk patients, a lower extremity ultrasound examination to exclude DVT should be repeated in 5–7 days to exclude propagation of an undetected calf thrombosis. Such a repeat examination would also catch a propagating 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, the test is not 100% accurate. Practitioners should understand the limitation of this examination, 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 pulmonary embolism is fraught with potential danger if the physician does not keep in mind that only a positive finding if helpful. Specifically, as many as two thirds of all patients with a pulmonary embolisms will not have a proximal DVT found on ultrasound. This makes sense as the thrombus has probably embolized to the lungs.38

5. Mistaking artery for vein. While this is not a common pitfall, novice sonologists 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 an uncompressible deep vein. This is especially true for inflamed lymph nodes. Figure 15-31 shows an example of a large lymph node that was mistaken for a femoral DVT. The lymph node is a finite structure and moving the transducer proximally or distally will allow the sonologist to identify the edges of the lymph node. Rotating the probe 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.39 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 some 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 computed tomography 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 of the venous flow in the common iliac vein. Normally, variation is seen in the baseline venous flow with respiration (Figure 15-32). 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 complete obstruction of proximal veins.

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.

Case 1

Patient Presentation

A 25-year-old woman presented to the emergency department 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 is 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 measures approximately 1.5 cm larger on the left, a fact the patient attributes to a left knee injury while playing soccer in college.

Management Course

The vascular laboratory was not open on Saturday and the on-call radiologist recommended that the patient be anticoagulated and admitted into the hospital until she could be imaged as the first case on Monday morning. The patient is originally from another state and did not have a primary care physician in the area. She insisted that she must study for her law school finals and, unless medically necessary, she would prefer to go home. She does voice concern regarding the possibility of a DVT as she noted her sister was “very sick” from her blood clot. 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 and complete obliteration of the lumen was seen with moderate compression. The popliteal vein was visualized behind the knee and also compresses normally. The patient was given appropriate instructions and was requested to follow up with the university's clinic Monday after her examinations. She was told that she should have a follow-up ultrasound evaluation in 5–7 days.

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. Conversely, if the patient were to be admitted to await an imaging study, she would spend the weekend in the hospital and miss her law school examinations. This scenario is quite realistic in many facilities. Staffing a vascular laboratory 24 hours a day, 7 days a week, can be too expensive, especially when coupled with a shortage of sonographers. Treating the patient with low-molecular-weight heparin as an outpatient may seem attractive, but has some limitations. The patient must be trained to administer the injections. Furthermore, while the risk of bleeding was low, it is present and could once again be a medicolegal issue for some physicians. In this case, the emergency physician was able to confidently exclude a proximal DVT and promptly discharge the patient. She could follow up in 2 days with the school's clinic and had a repeat ultrasound examination arranged to exclude propagation of a calf vein thrombosis.

Case 2

Patient Presentation

A 60-year-old man with a history of chronic obstructive pulmonary disease, arthritis, coronary artery disease, and hypertension presented to the ED with complaints of vague pain in his left lower extremity. The patient noted that he typically had pain in either or both legs and requested a prescription for rofecoxib, which had helped with the pain in the past. He denied any new leg swelling and stated that they were both a little swollen all the time. The patient further denied chest pain or shortness of breath and gave no history of thrombosis in the past.

Physical examination revealed a comfortable appearing man. The patient's vital signs were within normal limits with an oxygen saturation of 96% on room air. The cardiac and lung examinations were remarkable for distant heart sounds and coarse breath sounds. The lower extremity examination revealed venous stasis changes on both lower legs as well as tenderness at both knees and ankles on range of motion. The patient appeared to complain of calf pain on both sides but more so on the left. There was mild nonpitting edema. No palpable cord was felt and no erythema was seen posteriorly.

Management Course

The vascular laboratory was contacted but was unable to perform the examination for several hours due to a backlog from the floor. The patient asked to be discharged, stating that this was just his arthritis and he would see his own physician when he was back from vacation next week. A bedside ultrasound examination was performed and showed normally collapsing femoral veins. However, the popliteal vein did not collapse completely with compression (Figure 15-33). The partner covering the patient's primary physician was contacted and agreed to see the patient in the office the next morning if a low-molecular-weight heparin injection could be administered to the patient. The patient received an injection and was discharged to be seen approximately 12 hours later by his physician.

Commentary

Case 2 illustrates the utility of focused compression venous ultrasound. The patient had several confounding issues such a chronic arthritic pain and lower extremity swelling. However, he deserved an ultrasound evaluation to exclude thrombosis. The vascular laboratory, busy as most are, was not able to perform the examination for several hours. A rapid examination of the proximal deep veins in the affected leg revealed a popliteal DVT. The patient was able to be treated with an injection of low-molecular-weight heparin and was discharged to follow up with his physician. The care of the patient was simplified and saved a considerable amount of time.

Case 3

Patient Presentation

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

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

Management Course

The patient is seen at night and no vascular laboratory testing is available. A bedside ultrasound examination of the left leg is performed and shows normally collapsing femoral and popliteal veins. With no proximal clot detected, the patient is given a dose of parenteral clindamycin and is discharged on oral clindamycin. The patient is scheduled for follow-up the next day with the primary care physician, who is advised to obtain a follow-up lower extremity Doppler examination in 5–7 days to rule out propagation of an undetectable distal venous clot.

Commentary

In case 3, the patient is once again at low risk, but cellulitis must be differentiated from a possible DVT. The clinician's ability to perform a bedside ultrasound examination provided accurate diagnosis and rapid disposition of the patient.