Overview

Superficial vein thrombosis (SVT), also known as superficial thrombophlebitis, is a condition characterised by the formation of a blood clot in the superficial veins, which are veins that are close to the skin’s surface. Although this condition is not harmful in effect, it can lead to deep vein thrombosis (DVT) or even pulmonary embolism (PE; a blood clot travelling to the major blood vessels of the lungs). 

The incidence of SVT varies, with studies showing rates of 0.64 per 1000 residents in urban areas and higher rates among older populations, particularly those above the age of 60. Additionally, 24% of SVT patients have DVT and 4.7% have pulmonary embolism. This significant overlap highlights the potential severity of SVT, particularly if it is left undiagnosed or untreated.  

Despite SVT being viewed as benign, SVT carries real risks of progressing into more serious conditions. As a result, timely intervention and appropriate treatment are crucial, especially in patients with underlying risk factors such as pregnancy or a history of venous thromboembolism (VTE). 

This article provides a comprehensive overview of SVT, covering its causes, symptoms, diagnosis and management strategies. It also explores the potential complications and highlights preventative measures.  

SVT vs DVT

Both superficial vein thrombosis (SVT) and deep vein thrombosis (DVT) are forms of venous thromboembolism, but they differ significantly in location, severity and associated risks. Understanding these differences is crucial for appropriate diagnosis and treatment.

SVT occurs in superficial veins, which commonly include the saphenous veins in the lower limbs. However, DVT occurs in deeper veins like the femoral or the popliteal veins. As these veins are directly connected to the heart, they are more critical for proper blood circulation. Most of the symptoms are similar to one another, such as swelling and redness, but in cases of DVT, if pulmonary embolism has developed, then individuals may experience shortness of breath, chest pain, dizziness and even fainting. Due to DVT having more serious complications, treatment may vary and anticoagulation therapy may be needed.

Development of SVT

Superficial vein thrombosis (SVT) begins with tiny blood clots called microthrombi forming in the veins. Factors like vein wall damage and increased blood clotting can cause these small clots to grow into larger ones, known as macroscopic thrombi. As the vein’s inner lining (endothelial lining) is damaged, it triggers inflammation, causing platelets to migrate to the site As they stick together, they form a clot. This process is driven by pro-clotting substances like thrombin and thromboxane A2, which promote further platelet aggregation and clot expansion. This inflammatory response is what causes the classic symptoms of pain, redness and swelling. As the clot becomes larger, the inflammatory response will intensify.

How does a clot form?

A blood clot forms as part of the body’s natural response to injury to prevent excessive bleeding.

Initially, vasoconstriction will occur where the walls of the blood vessel will constrict to reduce blood flow to the affected area. This will then activate platelets and stick to the damaged area of the blood vessel. The blood clotting cascade is initiated by proteins. Fibrinogen is converted to fibrin, which creates a mesh-like structure, holding platelets in place, forming the clot.

Risk factors

Factors which will increase the likelihood of developing superficial vein thrombosis (SVT) include:

• Varicose veins - Enlarged, twisted veins, mainly found in the legs, causing blood to stagnate
• Pregnancy - Can last up to 6 weeks after childbirth due to the hormonal changes and increased pressure on the veins  
• Prolonged immobility - Lack of movement, for example, due to bed rest or long flights, as slows blood flow
• Obesity - Excess weight can put pressure on veins, making it harder for blood to flow efficiently, which can lead to venous stasis
• Age - The risk is higher for those above the age of 60; veins lose elasticity and blood flow slows down

Other medical conditions that promote inflammation or abnormal blood clotting will increase the likelihood of developing superficial vein thrombosis (SVT), like thrombophilia and Behcet’s disease. Some of these risk factors are shared with deep vein thrombosis (DVT).

Symptoms

Superficial vein thrombosis (SVT) mainly affects the legs but can be observed in the arms or the neck.

Common symptoms include:

• Pain, tenderness or swelling along the affected vein
• Warm and itchy skin over the clot
• Changes to the colour and texture of surrounding skin (e.g. reddened skin)
• A hard, cord-like feeling under the skin
• Localised inflammation, making the area feel warm to touch

Diagnosis

Ultrasonography is the preferred test for confirming superficial vein thrombosis (SVT), in both lower limb and upper limb cases, as it allows for easy exploration of superficial veins. This allows the clinician to detect a lack of compressibility and impaired blood flow, which is the same principle used for DVT diagnosis. It is important to conduct an ultrasonography as it helps doctors evaluate the extent of SVT and exclude the case of deep vein thrombosis (DVT).  

Ultrasonography

Ultrasonography is when a probe is gently pressed over the skin to visualise the veins beneath the surface. Normal veins compress easily, indicating the absence of a thrombus (a clot). In cases of superficial vein thrombosis, the affected segment of the vein will not compress. This is because the thrombus inside prevents full compression. Additional tests may include using  Doppler ultrasonography, which will assess the blood flow through the vein. In cases of SVT, blood flow is limited in a specific segment of the vein.

There is a risk of SVT progressing into DVT as well as pulmonary embolism (PE), which can be life-threatening. This is a gradual process, which may begin as superficial vein thrombosis, developing into deep vein thrombosis and eventually pulmonary embolism. PE is when the blood clot from a deep vein has travelled to the lungs. This can be fatal as it leads to a lack of oxygen, placing strain on the heart and potentially causing sudden death. Due to this becoming life-threatening, it is important to timely diagnose and manage a pulmonary embolism in a timely manner.

Treatment of SVT

If symptoms are mild, then treatment may not be needed, but if symptoms do not go away or worsen, then treatments may include anti-inflammatory medicines like NSAIDs (non-steroidal anti-inflammatory drugs, such as ibuprofen), compression stockings and blood-thinning medicine called anticoagulants. These will increase blood flow and reduce the risk of blood clots.

To help alleviate the pain, it is important to keep using the affected leg or arm to maintain a continuous blood flow. You can also apply a warm, moist flannel to the area for relief. If needed, over-the-counter pain relievers like paracetamol or ibuprofen can be used, it is recommended that you avoid these if have been prescribed blood-thinning medication.

Pregnant individuals who need an anticoagulant will need to use a low molecular weight heparin (LMWH) anticoagulant. This is important to note as it will not cross the placenta, which is safe for the mother and the baby. Additionally, individuals who are actively bleeding or have severe liver disease may face heightened risks when using anticoagulants. Ensure to consult with a healthcare professional before starting anticoagulants.

Summary

Superficial vein thrombosis (SVT) is a common condition, primarily affecting the lower limbs. This is generally considered to be a mild condition, but over time, this may lead to more serious complications like deep vein thrombosis (DVT). The diagnosis of SVT is usually clinical but confirmed through ultrasonography, which will allow you to evaluate the clot size, location and proximity to the deeper veins.

The treatment focuses on symptomatic relief, but in more severe cases, when the clot is near the saphenofemoral junction (SFJ) or if there is a risk of progression, anticoagulants may be prescribed. Prevention strategies include regular physical activity and managing underlying conditions like obesity. Though SVT can often resolve on its own, patients should monitor symptoms closely and seek medical attention if complications arise. Future research is needed to get a better understanding of SVTs’ true prevalence and guide optimal treatment strategies.