The potential pathologies discovered or evaluated on a peripheral venous duplex US study are extensive and beyond the scope of this article. This embryological remnant fails to involute and is associated with vascular malformations of the leg and chronic venous insufficiency. Occasionally anatomic variants may directly/indirectly contribute to pathology, such as a persistent sciatic vein. Additionally, accessory saphenous veins and tributaries with large diameters may accompany or run parallel to the GSV, and the small saphenous vein may or may not coalesce with the popliteal vein. In the lower extremities, the great saphenous vein (GSV) may occur by itself, duplicated, or with a hypoplastic middle portion. Common upper extremity variants include unpaired brachial veins and low-lying basilic veins. Variant anatomy presents a challenge to any imaging study, especially the peripheral venous system, which has a wide breadth of normal variants. The latter effect may be avoided by careful attention to settings and scanning techniques during the study. Lastly, turbulence may be artifactual when the Doppler sample gate is erroneously placed immediately adjacent to the vascular wall, thus showing local turbulent effects rather than turbulence throughout the vessel. Additionally, turbulence may be caused by normal anatomic structures such as in the carotid bulb. Ī number of pathologies may cause turbulence-common entities include stenosis, pseudoaneurysm, and arteriovenous fistulas. Turbulent blood flow can create spectral broadening and/or an aliasing artifact. By contrast, unhealthy, diseased, or obstructed vessels demonstrate irregular mixing and flowing patterns known as turbulence. This laminar flow is demonstrated by a narrow spectrum or similar shades of a single color on spectral/color Doppler respectively.
The particles in the middle layer maintain the highest velocity. Blood generally travels in a laminar flow type pattern throughout the vascular system, meaning the blood moves in the same direction while distinctly divided within layers at different but similar velocities without intermixing. Peripheral veins return blood from the extremities against gravity by relying on a system of pumps (heartbeats and skeletal muscle movements), a pressure gradient, and one-way bicuspid valves. From superficial to deep, veins have an outer layer composed mainly of collagen (tunica adventitia), a smooth muscle layer (tunica media), and the innermost layer of the endothelium (tunica intima). On a US examination, healthy arteries and veins can be differentiated by noting the pulsations in the arteries, which are not readily visible in veins, and by the coaptation of venous lumens with mild compression.
Deep veins lie within the muscular fascia, superficial veins lie external to the muscular fascia and drain the cutaneous microcirculation while perforating veins connect these two. Generally, peripheral veins may be divided into three categories: deep veins, superficial veins, and perforating veins.
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