Clinical Findings. The clinical picture of deep vein thrombosis (DVT) stretches between the extremes of phlegmasia coerulea dolens and totally asymptomatic disease. In the former, massive thrombosis of the complete venous cross section results in acral gangrene due to a rise in tissue pressure above capillary pressure. Between these extremes lies the typical DVT, quite easily recognizable on the basis of edema, livid discoloration, petechiae
(which may rarely progress to extensive subcutaneous hemorrhages), and calf tenderness. General symptoms are not usually prominent, as long as pulmonary embolism has not occurred. Subfebrile temperature, moderately elevated ESR, and leukocytosis may be
present.

Diagnostic Approach. Early diagnosis may be difficult. Large surveys show that only 50−60% of cases are correctly diagnosed based on physical examination. Comparative palpation of the calves (subfascial edema), inspection of the standing patient (unilateral livid discoloration
of the foot, bulging veins on the back of the foot), and prominent subcutaneous collateral veins may indicate the diagnosis.

Clinical suspicion always requires additional diagnostic tests in order to confirm or rule out the diagnosis of DVT. Currently, direct visualization of the thrombosis is achieved primarily by B-mode ultrasound (compression ultrasound) or color-coded duplex ultrasound, which have an accuracy of approximately 95%. Simpler technical procedures like Doppler ultrasound
and plethysmographic techniques have become of minor significance for the diagnosis of DVT. Plethysmography is an indirect method, which detects abnormalities in venous outflow caused by the thrombosis. A negative D-dimer test rules out DVT with high probability. Phlebography is used predominantly in uncertain cases to achieve a definitive diagnosis. Phlebography is mandatory before aggressive treatments like surgical thrombectomy or fibrinolysis.

Types of lower limb DVT. Calf vein thrombosis is the most common form and at the same time the most difficult to diagnose, since its course is frequently bland. Involvement of the veins of the thigh (ascending form) not only increases the risk of pulmonary embolism, but also of future development of severe chronic venous insufficiency. Thrombosis of the pelvic veins and multilevel thrombosis usually causes unequivocal symptoms, except when the thrombus occludes the venous lumen only partially.

Causes. summarizes the most important factors predisposing to DVT. Compression of the left common iliac vein by the right common iliac artery is probably the reason why DVT is more common in the left than in the right leg. An actual fibrous stenosis is occasionally seen at this site of compression (May−Thurner syndrome). DVT is still regularly seen after surgery and trauma, although its frequency has been reduced by pharmacological thromboembolic prophylaxis. Hip replacement surgery is one of the most common causes. However, it is important to stress that several medical conditions like heart failure, myocardial infarction, stroke, and malignant neoplasias also have a high risk of DVT. Differential diagnosis of venous stasis should include causes of localized venous compression (tumors, aneurysms, Baker cyst, or large, subfascial hematoma), and paresis with failure of the muscle pump (e. g., residual state after poliomyelitis).