Where are blood clots on the leg typically located?

Location of Blood Clots in the Leg

Blood clots in the leg most commonly occur in the deep veins of the calf (peroneal, posterior tibial, and anterior tibial veins), the thigh (femoral and popliteal veins), and the pelvis (iliac veins), with 70-90% of lower extremity DVT occurring in the femoral and iliac veins when the source can be identified. 1

Primary Anatomical Distribution

Proximal Deep Veins (Most Common and Highest Risk)

• The femoral and iliac veins are the most frequently affected sites, with up to 77% of cases involving pelvic veins when present 1
• Approximately 25% of all lower limb DVT cases involve the iliac veins 1
• The popliteal vein (behind the knee) is another common proximal location 2, 3
• Proximal DVT carries the highest risk of pulmonary embolism (67-77%) and post-thrombotic syndrome 1

Calf Veins (Distal DVT)

• Calf vein thrombosis occurs in approximately 69% of patients with DVT and is isolated to the calf in 33% of cases 4
• The peroneal veins are involved in 81% of calf DVT cases, posterior tibial veins in 69%, and anterior tibial veins in only 21% 4
• Isolated calf DVT has a lower pulmonary embolism risk (46%) compared to proximal DVT 1
• Most DVT starts in the calf, though many resolve spontaneously without extending proximally 5

Clinical Significance by Location

Risk Stratification Based on Location

• Iliofemoral DVT is associated with the highest risk of post-thrombotic syndrome and serious complications 1
• The incidence of pulmonary embolism increases progressively: 46% for calf-only DVT, 67% for thigh involvement, and 77% when pelvic veins are involved 1
• Proximal DVT (femoral and iliac) requires more aggressive treatment consideration, including potential mechanical thrombectomy or catheter-directed thrombolysis 1

Diagnostic Considerations by Location

• Ultrasound has high sensitivity (94.2%) and specificity (93.8%) for proximal DVT but much lower sensitivity (63.5%) for distal calf DVT 2
• Iliocaval DVT may be missed on standard ultrasound because thrombus extends above the typical examination area; whole-leg swelling with normal compression ultrasound suggests central obstruction 6
• The peroneal and posterior tibial veins are more difficult to visualize on ultrasound, with peroneal veins being inadequately scanned in 29 cases out of 696 limbs in one study 4

Common Pitfalls in Location Assessment

• Limited ultrasound protocols examining only thigh-to-knee miss potential calf vein thrombosis and require repeat study in 5-7 days 6
• Isolated femoral vein thrombosis may be missed by limited 2-region compression ultrasound 6
• About 50% of diagnosed pulmonary embolism cases have concurrent lower extremity DVT, even when leg symptoms are absent 5
• Compression ultrasound should be performed at 2-cm intervals from the inguinal ligament to the ankle to avoid missing segmental thrombi 6