Left “Mickey mouse” sign and deep vein thrombosis
Compression ultrasound manoeuvre is the gold standard for the diagnosis of deep vein thrombosis (DVT). The manoeuvre consists in applying a gentle pressure over the transducer once the vein to be assessed has been identified. If under such pressure the walls of the vein being examined do not collapse, then the lumen is not echo free and is suggestive of the presence of an intraluminal thrombus. This represents the main direct ultrasound criteria for the identification of deep vein thrombosis and it is usually performed using B-mode image and transverse view.
In this example, figure 1 shows a B-mode transverse view of the vessels at the level of the groin that usually form a typical ultrasound image, the so called Mickey mouse sign. The Mickey mouse image is formed by the common femoral vein (CFV), representing the face, the great saphenous vein (GSV) and common femoral artery (CFA) representing the ears. Mixed echogenic material can be seen within the lumen of the CFV extending into the origin of the GSV (the intralumen visualisation of the thrombus is another direct criteria for the diagnosis of thrombosis).
Figure 2 shows the same transverse B-mode view, in presence of a gentle pressure applied over the vessels forming the Mickey mouse sign. Compared to figure 1, there is a partial compression of both veins; however, the venous walls do not collapse completely as per the presence of the intraluminal thrombus. The CFA usually does not collapse under the pressure due to the higher intraluminal arterial pressure.
Figure 3 demonstrates the same transverse view using colour flow Doppler. Colour flow Doppler may help in better defining the borders of a thrombus, especially if this is hypoechoic and difficult to define. However, it is important to use the correct setting, as a too low scale may cause colour flow saturation and override the actual thrombus.