24.2 Venous Extremity Doppler

Lower-Extremity DVT Protocol

The goal of venous duplex sonography is to detect or exclude deep vein thrombosis (DVT). Begin at the groin with the common femoral vein at the inguinal crease and proceed distally through the femoral vein (the old term "superficial femoral vein" is discouraged — it is part of the deep system), into the popliteal vein behind the knee, and finally the paired calf veins (posterior tibial and peroneal). The single most important maneuver is transducer compression: apply gentle probe pressure in the transverse plane approximately every 2 cm along the vein. A normal vein fully coapts — the anterior and posterior walls touch and the lumen disappears. Any residual lumen under compression indicates thrombus (or chronic wall change).

Complementary Doppler findings confirm patency and physiologic behavior:

• Spontaneity: flow is present without provocation
• Phasicity: venous velocity rises and falls with respiration — decreasing with inspiration and increasing with expiration; loss of phasicity (a continuous, flat signal) suggests obstruction proximal to the transducer, such as iliac or caval thrombus
• Augmentation: a brisk squeeze of the calf distal to the probe produces a surge of flow, confirming the segment between the squeeze point and the transducer is patent
• Valsalva at the common femoral vein can demonstrate valve closure and central patency

Normal lower-extremity venous spectral Doppler shows low-velocity, phasic, non-pulsatile flow; a pulsatile or arterialized venous signal is abnormal.

Acute versus Chronic Thrombus

Distinguishing acute from chronic thrombus changes management, because acute clot is the embolic risk and responds to anticoagulation, while chronic change is largely irreversible. Acute thrombus is anechoic to hypoechoic, gently distends the vein (its diameter often exceeds that of the adjacent artery), and renders the vein noncompressible; the clot may be loosely attached, with a free-floating tail visible in the lumen. Chronic thrombus becomes increasingly echogenic and organized: the vein contracts to a small caliber, the wall thickens, and you may see synechiae (echogenic webs), recanalization channels carrying flow through the old clot, and collateral veins bypassing the occluded segment. Chronic disease also destroys valves, producing reflux with augmentation or Valsalva. A useful memory aid: acute = distended, hypoechoic, noncompressible; chronic = contracted, echogenic, collateralized.

Upper-Extremity Protocol

Upper-extremity studies (commonly ordered for arm swelling, PICC line evaluation, or dialysis access planning) cover the internal jugular, subclavian, axillary, brachial, basilic, and cephalic veins. The mid-subclavian vein and the jugular-subclavian confluence cannot be compressed because the clavicle overlies them. Here Doppler surrogates replace compression: loss of respiratory phasicity, loss of transmitted cardiac pulsatility, and an absent response to distal augmentation imply central obstruction. A normal subclavian signal is pulsatile and phasic; a dampened, continuous waveform at the confluence suggests brachiocephalic or superior vena cava obstruction.

Superficial Disease and Its Mimics

Superficial thrombophlebitis most often involves the great saphenous vein (GSV) and presents as a tender, palpable cord. It matters mainly when thrombus approaches the saphenofemoral junction: clot within about 3 cm of the junction may propagate into the deep system, and treatment thresholds then mirror DVT. Always document the distance of the thrombus tip from the junction. Involvement of the small saphenous vein near the saphenopopliteal junction carries the same concern. A classic DVT mimic is the ruptured Baker (popliteal) cyst: a pre-existing fluid collection behind the knee decompresses and dissects down the calf, producing acute pain and swelling — but the deep veins compress normally, and ultrasound instead shows fluid tracking along the medial gastrocnemius fascial planes. Cellulitis, muscle tears, and lymphedema are other common mimics.

Patient Positioning and Technical Factors

Scan the patient supine in slight reverse Trendelenburg with the leg externally rotated and the knee gently flexed, which fills the popliteal and calf veins. Veins are superficial, so a mid- to high-frequency linear transducer (about 5-9 MHz) works for most of the leg; drop to a curvilinear or lower-frequency probe in the thigh of larger patients or when the iliac segment must be assessed. Keep spectral Doppler angles at 60 degrees or less and the sample volume centered in the lumen. Calf veins are best imaged from a medial approach with the patient sitting or the leg dependent, because hydrostatic pressure distends them and makes the paired posterior tibial and peroneal veins easier to follow; each artery is flanked by two veins, so identify the artery and survey both companions.

Post-Thrombotic Syndrome and Pitfalls

After DVT, valvular destruction and residual obstruction cause post-thrombotic syndrome: chronic aching, edema, venous claudication, and in advanced cases skin hyperpigmentation and ulceration, typically near the medial ankle. Two pitfalls deserve emphasis. First, a duplicated femoral vein — present in roughly 20-30% of patients — can hide thrombus in one of the two channels; always check for duplication when the vein appears small or clinical suspicion is high. Second, isolated calf-vein thrombus (posterior tibial, peroneal, soleal, or gastrocnemius veins) is easily missed if the survey stops at the popliteal vein. Most isolated calf clots do not embolize, but a significant minority propagate proximally if untreated, so current practice calls for anticoagulation or short-interval surveillance imaging. Muscular (soleal and gastrocnemius) vein thrombi are the most common isolated calf thrombi and follow the same surveillance logic.