Presented by Intern邱宏智 Radiology 2005 237: 348-352 Presented by Intern邱宏智

Objective To establish the safety of withholding anticoagulation therapy after negative findings at a complete lower limb ultrasonographic (US) examination of the symptomatic leg for suspected deep venous thrombosis (DVT).

Deep vein thrombosis Deep venous thrombosis (DVT) affects about 84 per 100 000 people each year Untreated DVT is associated with a high risk of pulmonary embolism (PE) Postthrombotic or postphlebitic syndrome False diagnosis of DVT results in unnecessary anticoagulant therapy, which is associated with a risk of bleeding

Introduction Objective testing for DVT is essential because clinical assessment alone is unreliable Ultrasonographic (US) examination limited to the common femoral vein, superficial femoral vein, and popliteal vein, with compressibility of the vein serving as the sole criterion for diagnosis, has been the reference standard for diagnosis of symptomatic lower limb DVT

Introduction This limited proximal US examination has nearly 100% sensitivity and specificity for proximal DVT, as measured with contrast venography However, the accuracy of US in the detection of isolated calf DVT is lower Since calf DVT can propagate proximally in one-third of cases, a second US examination is strongly recommended within 5–7 days to exclude DVT

To establish the safety of withholding anticoagulation therapy after negative findings at a complete lower limb ultrasonographic (US) examination of the symptomatic leg for suspected deep venous thrombosis (DVT).

Materials and methods Prospective study 542 consecutive ambulatory patients with suspected symptomatic lower limb DVT Emergency department of a tertiary hospital a latex agglutination immunochromatographic D-dimer assay

Objective Testing for DVT Complete real-time B-mode US examination with color Doppler flow analysis High-spatial-resolution linear-array transducers with variable frequency (6–8 MHz) probes Patients were lying in the supine position, with the symptomatic leg externally rotated and slightly flexed at the knee.

From the level of the inguinal ligament to the medial malleolus. The common femoral vein, superficial femoral vein, popliteal vein and trifurcation, and all three deep calf vein sets were examined. Compressibility of these veins was assessed at 2–3-cm intervals in the transverse plane.

Superficial femoral vein

Noncompressibility of a segment of the veins was the sole criterion for diagnosis of DVT. Doppler examination of these veins was performed for the purpose of acquiring supplemental information (only as map road) Anticoagulation therapy was withheld if the US findings were negative.

Compression ultrasonography

Follow-up After 3 months by telephone, and a questionnaire was completed for each patient The minimum follow-up period of 3 months was chosen on the basis of previous studies Three end point the patient was alive and had experienced no thromboembolic event the patient was alive and had evidence of a thromboembolic event the patient died within the follow-up period.

Patients in whom DVT was suspected because of new or progressive symptoms were objectively assessed with a repeat complete lower limb US examination. In patients in whom PE was suspected, computed tomographic (CT) pulmonary angiography was performed by using a single-detector row helical CT scanner If the CT pulmonary angiogram was negative, then a complete lower limb US examination was performed, as described previously.

Result 413 (78.5%) negative for DVT 113 (21.5%) positive for DVT 243 (46.2%) negative D-dimer 283 (53.8%) positive D-dimer Negative D-dimer findings, 14 (5.8%) had positive US findings and 229 (94.2%) had negative US findings positive D-dimer findings, 99(35%) had positive US findings, and 184 (65%) had negative US findings.

Positive for DVT 64 patients (56.6%) had DVT isolated to calf veins 49 patients (43.4%) had proximal DVT 59 men and 54 women,with an average age of 55.26 years 15.76 (age range, 18–88 years). A total of 26 patients had a history of previous DVT or PE, and 14 patients had a history of active malignancy.

The negative predictive value of a complete single lower limb US examination to exclude clinically important DVT is 99.6%

Discussion The current diagnostic strategies for lower limb deep venous thrombosis: serial above-knee compression US examinations, with the second US examination performed 5–7 days after the initial US examination combination of a single above knee compression US examination with a negative D-dimer assay Combination of pretest probability and twopoint compression US and venography to exclude DVT

DVT was documented in 3, 17, and 75 percent of patients with low, moderate, or high pretest probabilities, respectively. Lancet 1997 Dec 20-27;350(9094):1795-8.

If we use above-knee compression US, serial examination is necessary to detect propagation of calf vein thrombi proximally. Because the prevalence of proximal DVT in ambulatory outpatients varies from 9% in the current study to 28% in a study performed by Bernardi et al ; the rate of repeat US in up to 90% of patients is of low clinical efficiency,

Though a complete lower limb US examination would take 10–15 minutes longer than a limited above-knee US examination, the second above-knee US study required would consume substantial resources, present an inconvenience to patients, and not always be practical

it is safe to withhold anticoagulation therapy after a single negative complete lower limb US study, with only one patient (0.2%) experiencing a nonfatal PE 4 days after the initial US examination favorable when compared with previous strategies

The proportion of isolated calf DVT is 56% (64 of 113 patients) in our study, which is greater than the rate observed in other studies (31%–45%) This may be because the general practitioners referred patients to the emergency department at an earlier stage of the disease spectrum than did physicians in other studies

Though isolated calf thrombi present a therapeutic dilemma (ie, whether to start anticoagulation therapy or not), the sixth American College of Chest Physicians consensus conference on antithrombotic therapy recommends symptomatic isolated calf DVT be treated with anticoagulant medications

Patient body habitus, especially obesity, results in an inability to obtain technically adequate US examinations of calf veins

The D-dimer test results are rarely negative, with a 500-ng/mL (enzyme-linked immunosorbent assay D-dimer) conventional cutoff value in inpatients, and it does not contribute to the diagnostic strategy of combining a negative D-dimer result with results of an above-knee compression US examination to rule out DVT

only the symptomatic leg rather than both legs with US It has been debated whether bilateral US imaging should be performed in patients in whom unilateral DVT is suspected

Summary In summary, it is safe to exclude clinically symptomatic lower limb DVT with a single complete lower limb US examination, and anticoagulation therapy can be withheld, with a low failure rate. this strategy would save time and be more convenient for imaging departments if it were used in ambulatory outpatients with suspected symptomatic lower limb DVT.

Thanks for your attention

Differentiation     Muscle strain, tear, or twisting injury to the leg — 40 percent     Leg swelling in a paralyzed limb — 9 percent     Lymphangitis or lymph obstruction — 7 percent     Venous insufficiency — 7 percent     Popliteal (Baker's) cyst — 5 percent     Cellulitis — 3 percent     Knee abnormality — 2 percent     Unknown — 26 percent

Prospective studies have demonstrated that lack of compressibility of a vein with the ultrasound probe is highly sensitive (>95 percent) and specific (>95 percent) for proximal vein thrombosis Color flow imaging, in addition to duplex Doppler ultrasound, is a less demanding study and is also highly accurate for the diagnosis of above the knee DVT In comparison, the presence of an echogenic band, although sensitive for DVT, has a specificity of only about 50 percent The variation of venous size with the Valsalva maneuver has a low sensitivity and specificity for the presence of DVT and is not performed in many centers

Compression ultrasound Limitations It does not detect isolated thrombi in the iliac veins or superficial femoral veins within the abductor canal. As with impedance plethysmography, the results are limited in patients with deformities or a plaster cast. Serial studies need to be performed when the initial test is negative; approximately 2 percent of patients with an initially negative ultrasound develop a positive study when retested seven days later. A single repeat study that is negative five to seven days after an initial negative study predicts a less than 1 percent likelihood of venous thromboembolism over months of follow-up Patients with pelvic neoplasms or abscesses may demonstrate isolated noncompressibility of the femoral vein when thrombosis is absent  It is less useful than impedance plethysmography for recurrent DVT. As noted above, only 60 to 70 of studies return to normal at one year compared to over 90 percent with impedance plethysmography

Extended (complete) lower extremity ultrasound routine compression ultrasonography has certain limitations, two of which are the lack of detection of iliac vein disease and the need for serial studies, with which the patient may not comply, if the first is test is negative and clinical suspicion is high. The generalizability of these observations may be limited because the quality of complete lower extremity ultrasound studies is operator-dependent

Sn = TP / (TP + FN) Sp = TN / (TN + FP) PPV = TP / (TP + FP) NPV = TN / (TN + FN)