Deep Vein thrombosis (2)

to continuing our atricle before
Proportion of DVT cases with clot at each location. Note that all clots in this series involve either the popliteal vein, femoral vein, or both. From Lansing AW, Hirsh J, Buller H, Diagnosis of Venous Thrombosis. In Colman RW, Marder VJ, Clowes AW, George JN (ed) Hemostasis and Thrombosis: Basic Principles. 3rd ed. Philadelphia. Lippincott, 2001, pp. 1305.

Of the femoral triangle, just inferior to the inguinal canal. At this level, the CFV is distinct from the GSV,which separates to take a more superficial andmedial course as it moves distally. The common femoral artery (CFA) at this level has not yet bifurcated.Here the CFV has bifurcated into the superficial femoral vein (SFV) and deep femoral vein (not visualized at this level). The CFA has now bifurcated into the super- ficial femoral artery (SFA) and deep femoral artery (DFA).

In general, the PV is superficial to the PA. There is occasional anatomic variability so that the artery is more anterior to the vein. This can be distinguished by using adjunctive methods such as spectral and color Doppler and compression. Technique Probe Selection For the evaluation of DVT, a high-frequency linear array probe is best. In larger patients or in patients with lower extremity edema, lower-frequency probes allow for better penetration of the sound beams; however, the image can usually be obtained with the high-frequency linear probe (5–10 MHz).


Views
At least two views are necessary:
1. Common femoral vein demonstrating compression of vessel – this usually
involves visualizing both the common femoral and greater saphenous
veins as seen in Figure 8.4. Some authors have argued that it is prudent
to compress both the common femoral and greater saphenous veins
and then to slide distal to the femoral triangle to compress the superficial
femoral vein as well, but this is not universally accepted.
2. Popliteal vein demonstrating compression of vessel
The simplified compression technique is performed by using the highfrequency
linear probe and identifying the common femoral and popliteal
veins. In Figures , probe positioning for femoral vein and popliteal
vein visualization is demonstrated. The probe marker should be directed
toward the patient’s right side.
If the veins are collapsible to a thin line with external pressure applied (Figure
8.9), the vein is presumed to be patent and there is no clot present. If the
vein does not collapse with external pressure, there is presumed to be clot
within the lumen of the vessel preventing complete collapse.
There are a few structures that can be mistaken for a noncompressible vessel
and that are worth mentioning. Lymph nodes can look like clot within a
hypoechoic vessel because they have a ring of hypoechoic fluid surrounding
the node. However, they are easy to distinguish because if the probe is turned

longitudinally, it will become obvious that the object is circular and not tubular.
Baker’s cysts can cause the same phenomenon in the popliteal fossa but
again dynamic scanning in longitudinal and transverse planes should remove
any doubt. Pseudoaneurysms and groin hematomas can also be misleading,
and caution should be exercised in clinical situations where these diagnoses
are being considered. This is where color Doppler can often be helpful

Scanning Tips

1. Proper patient positioning can greatly improve image quality.Have the patient externally rotate his or her leg to better visualize thecommon femoral vein.
2. For the popliteal vein, have the patient hang his or her leg over the edge of the bed to distend the vessels, or perform the scan with the patient in a prone position.
3. Be sure the veins fully compress. A normal vein will completely disappear when compressed enough; if the walls do not touch, consider DVT.
4. Make sure you are applying pressure evenly. The probe should be perpendicular to the skin. If pressure is being applied at an angle, the vessel may appear not to collapse because of unevenly distributed pressure.