| Lower Extremity Venous Anatomy and the use of Ultrasound for Detecting and Diagnosing Thrombus By: Erika Godfrey |
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Abstract
A thorough understanding of the anatomy of the lower extremity venous system is necessary to appreciate the role of duplex imaging. Evaluation and treatment of venous thrombosis disease is primarily performed by duplex ultrasound and compression. Duplex ultrasound provides accurate information of normal and abnormal vessels. This article describes anatomy of the lower extremity venous system and normal and abnormal imaging of thrombosis. |
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Key words:
deep veins, superficial veins, duplex imaging, acute, subacute, and chronic thrombosis
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Introduction:
The venous system of the lower extremities is composed of deep and superficial veins. Other vessels include venous sinuses and communicating veins. Each of these vessels contributes to the draining of venous blood from the lower extremity. Venous thrombosis of the lower extremities is a common mechanism of disease. Methods for detecting and diagnosing thrombus are Ultrasound duplex imaging and compression of the veins. |
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The deep system begins in the abdomen at the inferior vena cava (IVC) and common iliac veins. The common iliac veins are formed at the junction of the internal and external iliac veins. The external iliac vein becomes the common femoral vein (CFV) just below the inguinal ligament. The CFV becomes the superficial femoral vein and deep femoral (or profunda) vein. The femoral vessels lie deep to the corresponding arteries. The SFV continues down the thigh and passes through the adductor canal. At this point, it becomes the popliteal vein. The popliteal vein runs along the medial aspect of the thigh to the back of the knee. It lies superficial to the popliteal artery. The popliteal divides just below the knee into three deep-paired vessels of the calf. It first bifurcates into the anterior tibial veins (ATV) and the tibioperoneal trunk. The anterior tibial veins branch laterally and drain the front portion of the calf. The tibioperoneal trunk bifurcates into the posterior tibial veins (PTV) and peroneal veins. The posterior tibial veins travel medially and drains the back of the calf. The peroneals drain the lateral region of the lower calf. |
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Located within the calf muscles are venous sinuses. These are dilated channels that allow the venous blood to accumulate before draining. The soleal veins empty the soleal muscle into the posterior tibial and peroneal veins. The gastrocnemus veins empty the gastrocnemus muscle into the popliteal. These vessels are potential and common sites for venous thrombosis. |
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The greater saphenous vein (GSV) and lesser saphenous vein (LSV) make up the superficial system. The GSV is the longest vein in the body. It empties into the CFV at the saphenofemoral junction in the groin. It travels medially and extends to the dorsum of the foot. The GSV serves as primary collateral when there?s occlusion in the deep system. The LSV runs posteriorly along the calf and empties into the popliteal vein. The perforating veins are communications between the superficial and deep systems. Blood travels from the superficial veins through the perforators into the deep veins. |
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There are different mechanisms of disease involved in the lower extremity venous system. Deep venous thrombosis (DVT) is the principal disease of the deep system. The thrombus frequently originates in the cusps of valves. As the clot progresses blood flow will restrict causing an increase in venous pressure. The vein walls will stretch causing damage to the valves. The entire clot or part of it can break loose and cause a pulmonary embolism, which can be life threatening. Contributing factors of DVT include venous stasis, trauma, hypercoagulation, age, heart failure, and previous DVT. |
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| Venous thrombosis in the superficial system (SVT) is not as threatening as DVT. SVT can cause superficial phlebitis, an inflammation of the vessels, resulting in a palpable cord throughout the vessel |
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Ultrasound is the primary imaging technique used to detect venous thrombosis. Spectral Doppler can detect the presence of thrombus by determining normal or abnormal flow in the vessels. Normal Doppler will be unidirectional and spontaneous with respiratory phasicity. Flow should cease with Valsalva maneuver, and demonstrate augmentation by distal compression. The Doppler will appear abnormal when there is substantial occlusion of the vein. Flow augmentation and Valsalva will be diminished or absent. Color Doppler is a valuable asset to venous imaging. It demonstrates direction and the amount of blood flow in the vessels. |
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The most reliable method for detecting thrombus is compression. Compressions are done in gray scale in a transverse plane. The thrombus can only be ruled out when vessel walls completely coapt. Partial thrombosis may be present if the entire vein does not collapse. |
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Image characteristics will appear differently along with each phase of the thrombus. Fresh or acute thrombosis refers to clots that are days up to two weeks old. Acute thrombus appears spongy in texture and is poorly attached to the vessel wall. The vein will be distended abnormally larger than usual. Venous distension helps to differentiate between newly formed and older thrombus. Newly formed clot generates low level echoes and may be anechoic. This will make imaging difficult. The use of color Doppler will help indicate blood flow to the vessel. A lack of flow indicates the presence of thrombus. The subacute phase refers to clots that are weeks up to two months old. The thrombus gradually becomes more echogenic. Retraction and lyses of the thrombus will reestablish patency and occupy less of the vein lumen. The vein becomes less distended and returns to a normal size. The chronic phase refers to clots that are months to years old. Chronic thrombus appears rigid in texture and is well attached to the vessel wall. Echogenicity is strongly increased in this phase. Echogenic intraluminal material may resemble plaque and cause acoustic shadowing.
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Conclusion
Ultrasound duplex imaging of the venous system has played a major role in the evaluation and treatment of venous disease. Duplex examination provides accurate information in determining the age and phase of thrombus. Color Doppler can demonstrate direction and the amount of blood flow in the vessel. Ultrasound duplex imaging along with compression can identify and rule out venous thrombosis. |
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Bibliography
. Patton, Kevin T. and Thibodeau, Gary A., Anatomy & Physiology 4th Edition. St. Louis: Moby Inc., 1999
. Ridgway, Donald P., Introduction to Vascular Scanning 2nd Edition. Pasadena: Davies Publishing Co., 2001
. Zwiebel, William J., Introduction of Vascular Ultrasonography 4th Edition. Philadelphia: W.B. Saunders Co., 2000
. Cury, Reva Arnez and Tempkin, Betty Bates., Ultrasound: An Introduction to Normal Structural and Functional Anatomy. Philadelphia: W.B. Saunders Co., 1995
. Rumwell, Claudia and McPharlin., Vascular Technology. Pasadena: Davies Publishing Co., 2000
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Erika Godfrey 9-17-2002 Vascular 135
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Copyright CVTC 2003. All Rights Reserved.