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1
Department of Radiology, University of Pennsylvania Medical Center, Hospital
of the University of Pennsylvania, 3400 Spruce St., Philadelphia, PA
19104.
2
Present address: Scottsdale Medical Imaging, Ltd., 7624 E. Indian School Rd.,
Scottsdale, AZ 85251.
Received January 24, 2000;
accepted after revision March 28, 2000.
Presented at the annual meeting of the American Roentgen Ray Society,
Washington, DC, May 2000.
Abstract
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MATERIALS AND METHODS. The results of 2704 lower extremity venous sonograms, obtained in 2026 consecutive patients over a 4-year interval, were reviewed retrospectively. The distribution of acute deep venous thromboses across various lower extremity venous segments was analyzed for this population, which consisted of both symptomatic and asymptomatic patients.
RESULTS. Of 2704 lower extremities studied with duplex sonography, acute deep venous thrombosis was identified in 269 (9.9%). Of these 269 cases, acute deep venous thrombosis was isolated to the superficial femoral vein in 60 (22.3%). The remaining 209 cases (77.7%) showed thrombus that extended into the common femoral or popliteal veins (or both).
CONClUSION. An abbreviated imaging study that evaluates only the common femoral and popliteal veins would fail to identify more than 20% of lower extremity acute deep venous thromboses in a population like ours. Although evaluation of the superficial femoral vein requires additional time and resources, evaluation of this segment may prevent a substantial number of thrombi from being missed.
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Although untreated deep venous thrombosis may occasionally extend over a long segment, such as from the iliac vein to the calf, acute deep venous thrombosis typically presents as either isolated calf-popliteal thrombosis, or as iliofemoral thrombosis [2,3,4]. Thus, it has been suggested that limiting the routine venous sonography study to the common femoral vein and popliteal veins may substantially decrease the time required for performance of the examination without significantly decreasing the sensitivity of the study for clinically important deep venous thrombosis [3, 5, 6]. Nevertheless, there is some controversy as to whether the limited published data on the distribution of thrombi in acute lower extremity deep venous thrombosis support this change in technique. Thus, many centers continue to evaluate the entire deep venous system from the common femoral vein to the trifurcation of the popliteal vein [4].
The purpose of this study was twofold: one, to determine the typical distribution of acute thrombi in various segments of the lower extremity deep venous system; and two, to determine by extrapolation whether an abbreviated duplex sonographic examination that excludes evaluation of the superficial femoral vein can provide a sensitive examination for acute deep venous thrombosis that is comparable with a routine duplex study of the complete deep venous system.
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Sonographic studies were performed with a model HDI or 3000 scanner (Advanced Technology Laboratories, Bothell, WA) on a linear or curvilinear transducer having a frequency of between 3.5 and 7.0 MHz. Transducer frequency and configuration were chosen to optimize imaging of the deep veins on a patient-by-patient basis. Sonographers, fellows, residents, and staff sonologists experienced in evaluating for lower extremity deep venous thrombosis performed all examinations.
Interrogation of the entire proximal deep venous system was performed in each case, including the common femoral vein, superficial femoral vein, and popliteal vein. The superficial femoral vein, extending from the take-off of the deep femoral vein to the adductor canal, was divided arbitrarily into proximal, mid, and distal thirds for reporting and tabulation of data. The diagnosis of acute deep venous thrombosis was based on standard criteria, including noncompressibility of the venous segment, in conjunction with color and Doppler examinations.
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A total of 2704 lower extremity sonograms in 2026 consecutive patients obtained over the time period studied were reviewed. Findings reflective of acute deep venous thrombosis were reported in 269 extremities, or 9.9% of all studies. As shown in Table 1, acute deep venous thrombosis was isolated to the superficial femoral system in 60 cases, or 22.3% of all studies with positive findings. The remaining 209 positive studies (77.7%) showed acute thrombus extending into the common femoral vein, popliteal vein, or both. In 56 studies (20.8% of all positive studies), thrombosis extended from the common femoral vein through the popliteal vein.
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Of the 678 patients (33%) who underwent a bilateral examination, acute deep venous thrombosis was found unilaterally in 39 patients (5.8%), bilaterally in 22 patients (3.2%), and in neither extremity in 617 patients (91%).
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A venous duplex study of the lower extremity venous system is composed of two components: gray-scale evaluation of vein compressibility and color Doppler evaluation of venous flow. In its normal state, the entire venous system from the common femoral vein to the popliteal trifurcation easily compresses, or collapses, with gentle compression by the sonography transducer. The inability to compress a segment of venous lumen forms the basis for the diagnosis of acute deep venous thrombosis on sonography [6, 7]. Color-flow Doppler analysis represents the other mode of duplex sonography that, in the presence of acute deep venous thrombosis, depicts an absence of flow within the venous lumen or incomplete filling of the lumen, but if color gain or velocity thresholds are not set appropriately, the potential for artifactual results is significant [8, 9]. However, if used together properly, compression sonography and color or spectral Doppler sonography are complementary and are thought by many to provide the most accurate means of diagnosis of acute deep venous thrombosis.
Calf-popliteal thrombosis is more common than iliofemoral thrombosis, particularly in orthopedic and other postsurgical patients [2]. Iliofemoral deep venous thrombosis occurs more frequently in patients in the peripartum state, patients with antiphospholipid syndrome, and patients with pelvic masses [4]. Although untreated deep venous thrombosis may occasionally extend over a long segment, such as from the calf to the iliac system, deep venous thrombosis usually presents as either isolated calf-popliteal thrombosis or as iliofemoral thrombosis [3, 4]. For this reason, it has been suggested that limiting venous sonography to the common femoral vein and popliteal veins may substantially decrease the time required for performance of the examination without significantly decreasing the sensitivity of the study for clinically important deep venous thrombosis [3, 5, 6].
In a study by Pezzullo et al. [6], compression sonographic examinations of 155 symptomatic patients were retrospectively reviewed for location of deep venous thromboses. In 99% of the patients, acute deep venous thrombosis was present in either the common femoral vein or popliteal vein, and it was isolated to the superficial femoral vein in only 1% of the patients. The authors concluded that, at least in their symptomatic population, an abbreviated sonographic examination was a viable alternative to (complete) routine sonography and decreased examination time by roughly 54%. However, Pezzullo et al. did not use color-flow analysis as an adjunct in the diagnosis of deep venous thrombosis, and thus subtle (nonocclusive) thrombus may have been missed with compression technique alone.
Frederick et al. [10] reviewed 755 sonographic examinations for the presence of acute deep venous thrombosis in various segments of the deep venous system. Acute deep venous thrombosis was found in 131 of the studies (17.4%). Of these positive studies, deep venous thrombosis was isolated to the superficial femoral vein in 4.6% of the patients; thus, an abbreviated sonographic study evaluating only the common femoral and popliteal veins would have identified more than 95% of the deep venous thromboses.
Because of a lack of any larger published sonographic studies on the distribution of deep venous thrombosis and because of the differing results of the studies reported, many medical centers continue to evaluate the entire deep venous system from the common femoral vein through the trifurcation of the popliteal vein [4]. However, evaluation of the entire superficial femoral venous segment is time-consuming, and it would seem cost-effective to eliminate this portion of the examination if sufficient data could support such a change. Furthermore, recent efforts have focused on trying to combine CT angiography of the chest (for evaluation of pulmonary embolism) with segmental CT of the calves, thighs, pelvis, and abdomen for evaluation of deep venous thrombosis [11]. Thus, it would be ideal to know with confidence if it is necessary to scan the entire lower extremity in such an algorithm or if scanning could simply be limited to the common femoral and popliteal veins.
In our patient population, acute deep venous thrombosis was most commonly seen in the iliofemoral and calf-popliteal regions, confirming results described previously [2,3,4]. Specifically, 77.7% of thrombi involved either the common femoral vein or popliteal vein, and nearly one fifth of these thrombi extended along the entire deep venous system. However, a substantial portion of our patient population (22.3%) had acute thrombi that were isolated to the superficial femoral venous system with no involvement of the common femoral vein or popliteal vein. This relative fraction of thrombi isolated to the superficial femoral vein was higher in our study than in the studies mentioned previously. This discrepancy may be related in part to our patient population, which consisted of both symptomatic and asymptomatic patients and which unfortunately could not feasibly be stratified retrospectively for logistic reasons.
One inherent weakness of this, and almost any, study of sonographic diagnosis of deep venous thrombosis is the lack of a gold standard. Indeed, it is now rare for a patient to undergo conventional venography for confirmation of deep venous thrombosis at most institutions, including our own. Given the costs, radiation, and complications associated with venography, it is unlikely that venographic confirmation of a clot could be achieved in any modern prospective or retrospective trial. Clinicians today typically are inclined to treat on the basis of an initial duplex examination or to wait several days and repeat the study for confirmation.
In summary, our data suggest that an abbreviated duplex study that excludes evaluation of the superficial femoral venous system would fail to reveal a substantial number of acute lower extremity deep venous thromboses. Evolving CT and MR algorithms, which evaluate the lower extremities for deep venous thrombosis after CT or MR angiography of the pulmonary vasculature, will likely need to study the entire superficial femoral venous system in addition to the common femoral vein and popliteal vein. Although evaluation of the superficial femoral vein requires additional technologist time and increased use of resources, the potential for having missed deep venous thrombosis appears substantial if this evaluation is not included.
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