March 29, 2021
The main function of the veins is to carry venous blood flow (without oxygen) back to the heart. The venous system of the legs is made of superficial and the deep veins. These veins can communicate between them via the perforator veins (small veins that pierce the muscular fascia). There are two main superficial veins in the legs. One that goes from the foot to the groin and is called the Great Saphenous Vein (GSV) and one from the foot to the knee crease at the back of the leg and is called the SmallSaphenous Vein (SSV). Both these veins empty the venous blood flow into the deep veins. Flow is pumped back to heart through these veins via one way bicuspid valves and thanks to the calf muscles (muscle pump) that squeeze the veins during exercise. When the valves stop working and/or the muscles get weaker, some of the venous blood is pooled back towards the feet. This is called venous reflux/venous incompetence. With time this ‘refluxing venous blood’ within the superficial veins can cause side veins to enlarge and becoming prominent on the skin surface. These are called varicose veins. Deep veins can also become incompetent. Surgery is often required so to fix the main cause of superficial venous reflux/venous incompetence and to remove varicose veins. In order to accurately plan a tailored treatment for patients with varicose veins and venous reflux, it is of paramount importance that the vascular surgeon knows exactly where the source of venous reflux is, its distribution in the leg veins and varicosities, where are the varicose veins and what are their connections with other veins in the leg.
The modality of choice for evaluating patients with venous reflux and varicose veins is venous duplex ultrasound. Duplex ultrasound uses the combination of different imaging modalities (hence Duplex). Each modality is used for a specific purpose. The first modality is called B-mode. This is shown on the ultrasound screen as black and white images and is mostly used to understand the anatomy of the veins in the legs, their courses, size and any connections to any abnormal veins. Moreover, by using B-mode, the vascular sonographer can determine whether there are any enlarged perforator veins, any pelvic veins, any clot within the superficial and deep veins and to evaluate any abnormality of the veins walls. There are some situation where a detailed examination of the abdominal veins needs to be carried out, depending on the findings of the lower limb venous scan.
The next step of the venous ultrasound examination is to perform a colour Doppler flow assessment. ColourDoppler allows to visualise the blood flowing within the veins in real time. In order to see whether the veins and valves are properly working, the vascular sonographer needs to perform intermittent compression of the calf and thigh muscles with the patient standing, while colour flow is displayed within the vein on the ultrasound scanner screen. When compression is applied to the leg muscles, the amount of colour flow through the vein will increase in intensity; upon release of the compression there shouldn’t be any of if very little Colour flow left within the vein examined. If venous reflux is present, the vascular sonographer can visualise a different colour within the vein that will persist for more than 0.5 seconds. This indicates the presence of venous reflux and the vein is defined incompetent (venous incompetency). Colour flow assessment is then performed within the varicose veins and deep veins. A careful search for significant incompetent perforating veins into the superficial veins is also made using Colour flow. The final step of the venous scan is to perform a pulsed wave Doppler examination of the veins. The pulsed wave Doppler is another ultrasound function that allows to confirm direction of venous flow, confirm venous reflux and its duration and suggest any possible proximal problem of the abdominal veins.
By integrating all the information obtained from the different ultrasound modalities, the vascular sonographer can produce a map of the venous reflux and varicose veins distribution and produce a diagram that the vascular surgeon will use as a guide for planning the best treatment for the patient.
Figure A: example of venous reflux (red colour) starting at the level of the junction of the GSV with the deep veins (the common femoral vein). The venous reflux (red) is extended to the proximal and mid GSV and then feeds main varicose veins in the thigh and calf. The GSV is competent (blue colour) from mid-thigh to the foot.
Example of Small Saphenous Vein reflux, starting from the junction with the deep veins. No varicose veins are seen. The top ultrasound image shows reflux observed using pulsed wave Doppler. The bottom ultrasound image shows what colour Doppler flow looks like within a vein.
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