Lower-Extremity Veins

Anatomy

The pelvic veins consist of the external, internal, and common iliac veins. The external iliac vein begins at the inguinal ligament and ends at the merger with the internal iliac vein ( Fig. 16-1 ). This vein is the direct continuation of the drainage of the lower-extremity blood, with small contributions from the anterior abdominal wall through the inferior epigastric veins, and from the pelvis through circumflex iliac and pubic veins. The right external iliac vein is initially located medial to the external iliac artery, but crosses posterior to this vessel before it is joined by the internal iliac vein. The left external iliac vein remains medial to the artery throughout its length. The external iliac vein may have a single valve.

The external and iliac veins join at roughly the level of the sacroiliac joints to form the common iliac veins. This occurs deep in the pelvis, so that the common iliac veins are angled both anteriorly and cranial. The common iliac veins do not have valves. The right common iliac vein has a vertical course posterior to the right common iliac artery. The left common iliac vein is located medial to the left common iliac artery. In order to join the inferior vena cava (IVC) on the right, the left common iliac vein passes underneath the right common iliac artery and anterior to the S1 or L5 vertebral body (see Fig. 13-11 ). This frequently results in broadening of the left common iliac vein and sometimes functional compression. The confluence of the common iliac veins forms the IVC.

The venous structures of the lower extremities are divided into superficial and deep systems, linked by perforating veins. The perforating veins direct blood from the superficial into the deep system ( Fig. 16-2 ). All veins of the lower extremity normally have valves. In contrast to the upper extremities, the deep veins of the lower extremity are the dominant drainage pathway.

The common femoral vein (CFV) is formed by the confluence of the femoral vein (FV) and profunda femoris vein (PFV). The CFV lies within the femoral sheath medial to the common femoral artery ( Fig. 16-3 ; see also Fig. 2-28 ). The smaller tributaries include the great saphenous vein (GSV), and the medial and lateral circumflex femoral veins.

The FV extends from the groin, where it is joined by the PFV, to the adductor canal. This vein is frequently referred to as the superficial femoral vein, or SFV, because of its anatomic proximity to the superficial femoral artery. However, this nomenclature can cause confusion when trying to distinguish between deep and superficial veins in the extremity, so the term femoral vein, or FV, is used in this text. The FV lies slightly deep and lateral to the superficial femoral artery in the thigh (see Figs. 15-3 and 16-3 ). This vein is duplicated or complex in up to 20% of patients ( Fig. 16-4 ). The adductor canal in the thigh marks the transition of the FV to the popliteal vein. The PFV runs alongside the profunda femoris artery, draining the same muscles that are supplied by this artery. In approximately half of individuals, the PFV communicates directly with the popliteal vein at the level of the adductor canal.

The popliteal vein is formed from the confluence of the tibial veins in the upper third of the calf. In relation to the anterior surface of the leg, the popliteal vein lies posterior to the popliteal artery. In relation to the skin of the popliteal fossa (the posterior surface of the knee joint) it is more superficial (see Fig. 16-3 ). This vein is duplicated or complex in 35% of the population. In addition to the tibial veins, the gastrocnemius, soleal, and sural veins, and the small saphenous vein (SSV) all drain into the popliteal vein.

The deep veins of the calf are paired structures that parallel each of the three tibial arteries (see Figs. 16-1 and 16-3 ). The posterior tibial and peroneal veins are larger than the anterior tibial veins owing to the larger muscle mass of the posterior and medial compartments. The posterior tibial vein is a continuation of the venous structures of the plantar surface of the foot, whereas the anterior tibial veins drain the dorsal aspect of the foot. The peroneal vein originates at the level of the ankle. The posterior tibial and peroneal veins are joined by deep muscular branches from the soleus veins in the calf, and perforating branches from the superficial veins. The tibial veins reside in the same fascial compartments as their companion arteries.

The primary components of the superficial veins of the leg are the GSV and the SSV (see Figs. 16-1 and 16-2 ). These are sometimes referred to as the long and short saphenous veins , but this text uses GSV and SSV. Both vessels lie within the subcutaneous fat of the lower extremity superficial to the fascial layers of the muscles ( Fig. 16-5 ). The location, toughness, and caliber of these veins contribute to their desirability as conduits for arterial bypass surgery. The GSV has its origins in the veins along the medial edge of the foot. At the ankle the vein becomes the GSV, which ascends along the medial aspect of the leg to join the CFV below the inguinal ligament. The GSV communicates with the deep system along its entire length through small perforating veins. These veins are of great importance in that they drain the saphenous vein into the deep system, where venous return to the heart is assisted by the pumplike action of muscular contraction and relaxation around the veins. Disruption of the valves in the perforating veins allows blood to drain out of the deep into the superficial system, which contributes to varicose veins (dilated, tortuous superficial veins). The GSV receives tributaries from the anterior and posterior accessory GSVs, and variably from the inferior epigastric and external pudendal veins, just before joining the CFV.

The lateral edge of the foot drains into the SSV, a small vein that ascends along the posterior midline of the calf in a groove between the medial and lateral bodies of the gastrocnemius muscle ( Fig. 16-6 ). The SSV joins the popliteal vein at or just below the knee joint. In some patients, the SSV also communicates with medial branches of the GSV through the vein of Giacomini, also known as the intersaphenous vein (see Fig. 16-2 ).

Key Collateral Pathways

The deep venous system of the lower extremity provides collateral drainage for the superficial veins and vice versa. The drainage afforded by just one system alone is frequently sufficient to avoid swelling and discomfort in a prolonged upright posture. Obstruction of the CFV and external iliac vein results in drainage through the profunda femoral veins to the internal iliac veins via gluteal and other pelvic veins. In addition, drainage through the ipsilateral abdominal wall veins and across the perineum to the contralateral CFV can occur ( Fig. 16-7 ).

Occlusion of one internal iliac vein results in drainage through the contralateral vessel. When both vessels are occluded, venous drainage through ascending lumbar, gonadal, and even inferior mesenteric veins can occur. Isolated occlusion of one common iliac vein results in retrograde flow in the ipsilateral internal iliac vein with cross-pelvic collateralization to the contralateral internal iliac vein. Occlusion of both the common and external iliac veins results in drainage through the pubic, inferior epigastric, and lumbar veins. Additional collateral drainage by lumbar, paraspinal, and other retroperitoneal veins can also occur. Occlusion of both common iliac veins is functionally identical to obstruction of the infrarenal IVC.

Imaging

Ultrasound is the primary imaging modality for the lower-extremity venous system. The procedure carries virtually no risk, can be successfully performed in most patients, and provides both anatomic and functional data. Massive obesity, severe edema, external orthopedic hardware, and large areas of abnormal skin can limit the study. The venous system from the tibial veins to the proximal CFV can be imaged with a 5- to 7.5-MHz linear transducer (see Fig. 16-3 ). Lower frequency transducers may be required in large patients and for the iliac veins. Superficial veins, such as the GSV, can be imaged with a 10-MHz transducer (see Figs. 16-5 and 16-6 ). Imaging of the pelvic veins with ultrasound is inconsistent owing to the depth and tortuosity of the vessels.

A complete examination involves visualization of all portions of the venous system from the iliac veins to the ankle. The ultrasound transducer is used to compress the infrainguinal veins, which is not possible in the pelvis. Color-flow Doppler evaluation can determine patency and flow direction. The walls of the vein should coapt with gentle pressure (see Fig. 16-3 A and B ). Noncompressibility is diagnostic of an intraluminal abnormality, usually a thrombus ( Fig. 16-8 and Table 16-1 ). The normal response to Valsalva maneuver is cessation of flow; a blunted response indicates proximal obstruction, and retrograde flow indicates valvular insufficiency (see Fig. 3-5 ). The patency of nonvisualized segments can be assessed indirectly by measuring the Doppler signal central to the area of interest while gently squeezing the calf (“augmentation”) (see Fig. 16-3 ). A sudden increase in velocity or flow is the expected normal response.

The femoral and popliteal veins can be imaged with the patient supine or in slight reverse Trendelenburg (head up, foot down). A tourniquet at the knee or dangling the calf over the edge of the examination table may be required to optimally visualize the calf veins.

Diameter measurements and mapping of the superficial veins are frequently performed before harvest for surgical bypass. The course of the saphenous veins and the major branch points should be marked on the skin with indelible ink.

Magnetic resonance venography (MRV) of the lower-extremity veins using two-dimensional time-of-flight (2-D TOF) or contrast-enhanced three-dimensional (3-D) gradient-echo techniques can be used to image the lower-extremity and pelvic veins. When 2-D TOF sequences are used, a superior saturation band with slice thicknesses of 5-8 mm eliminates arterial signal ( Fig. 16-9 ). Complex flow patterns in the pelvis frequently result in signal loss in the external iliac veins as they enter the pelvis and at the confluence with the internal iliac veins. Contrast-enhanced sequences are not susceptible to flow artifacts, although arterial signal can be confusing unless subtraction software is available. Blood-pool contrast agents are very useful for venous imaging. Anatomic sequences are important when venous compression by an adjacent mass is suspected.

The low cost and ready availability of ultrasound limits the need for MRV in most patients with lower-extremity venous disease. Lower-extremity magnetic resonance imaging (MRI) with MRV sequences is useful in the evaluation of venous malformations, congenital abnormalities of venous anatomy, and suspected isolated pelvic deep vein thrombosis.

Lower-extremity CT venography (i.e., infusion of contrast via a foot vein) is feasible with multidetector row technology (see Fig. 16-7 ). In general, lower-extremity venous imaging with CT is performed by imaging during the venous phase of a conventional injection of contrast ( Fig. 16-10 ). Venous phase imaging of the lower extremities and pelvis can be combined with pulmonary artery CTA in the evaluation of patients with suspected pulmonary embolism (PE). Arterial enhancement is always present, which can make identification of small and weakly opacified veins difficult. CT is an excellent choice when compression of iliac veins by a pelvic mass is suspected as the etiology of lower-extremity swelling.

Conventional contrast venography is rarely necessary. Ascending venography is performed with the patient on a tilting procedure table oriented for a reverse Trendelenburg position. A block is placed under the foot of the leg opposite the side under study. This allows the patients to support their weight on the normal leg when the table is tilted. A 21-gauge or smaller butterfly needle or intravenous catheter is inserted into a vein on the dorsum of the foot and secured in place. Ideally, the tip of the needle should be oriented toward the toes, but most of the time one is satisfied with any usable access. Finding a vein can be a challenge in patients with edematous feet. Application of gentle pressure with a thumb or two fingers can displace the edema and reveal a usable vein in these patients.

Low osmolar contrast with 30% iodine should be used. The contrast is loaded into three or four 50-mL syringes. The table is tilted head-up 30-60 degrees with all weight-bearing on the leg opposite to the side of interest. A tourniquet is placed around the ankle to force contrast into the deep system. Hand injection is used to control the amount of contrast in the veins during the study. The initial injection of 5-10 mL of contrast is watched fluoroscopically as it exits the needle ( Fig. 16-11 ). At the same time, the patient is questioned regarding pain at the injection site. The injection is stopped for obvious extravasation or persistent pain.

Filling of the venous system is monitored by intermittent fluoroscopy during continuous hand injection of contrast. The calf veins will be opacified in most patients with 50-80 mL of contrast. Images are obtained in three projections (anteroposterior and both obliques) using a large field of view coned side-to-side. Magnification views should be obtained of any area of question. Digital subtraction venography is usually not performed because contrast clears too slowly from the veins, resulting in poor image quality on subsequent images.

The contrast is followed as it ascends the leg. The saphenous vein, when opacified, should be included on the films. The iliac veins are filled by compressing the femoral vein, repositioning the table so that the patient is either flat or in mild Trendelenburg position, then releasing the femoral vein compression. The contrast-filled leg then empties into the iliac veins and proximal IVC.

When the study is completed, the foot is connected to an infusion of sterile saline or 5% dextrose solution. A minimum of 150-200 mL is infused to flush the contrast from the leg before removing the needle. Traditionally, an abdominal film is obtained after each venogram to evaluate renal excretion and contours.

Venography is a safe procedure, but requires 100-150 mL of contrast per limb and is time consuming. The overall complication rate is less than 5%.

Acute Deep Vein Thrombosis

Thrombosis of the deep veins of the lower extremity is thought to occur in adults with a yearly incidence of 1 per 1000. The cumulative risk of developing venous thromboembolism by the age of 80 years may be as high as 11% in men. Acute DVT is rare in children. The coagulation pathway is discussed in Chapter 1 . A number of conditions are believed to or are known to predispose patients to development of DVT ( Box 16-1 ). Nonocclusive thrombus is believed to form first in an area of slow flow in a valve cusp, followed by central propagation and occlusion.

DVT is left sided in 38% of cases, right sided in 32%, and bilateral in the remainder. The thrombus extends above the inguinal ligament in 8% of cases, between the knee and the inguinal ligament in 27%, and is isolated to the calf in almost 65%. Thrombosis limited to the iliac veins is unusual (<3%) and is often related to a pelvic mass, May-Thurner syndrome (see Chronic Venous Obstruction and Post-phlebitic Syndrome), or extension of internal iliac vein thrombus.

Asymptomatic PE is common in patients with proximal DVT, with up to 80% having abnormal results on pulmonary artery imaging. Conversely, DVT can be demonstrated in 80% of patients with symptomatic PE. Approximately 20%-30% of patients with symptomatic DVT also present with symptomatic PE. The risk of PE is higher with proximal thrombus (extending above the popliteal vein), but PE also occurs in approximately 10% of patients with isolated calf DVT. Post-thrombotic syndrome (see next section) occurs in 40%-60% of patients within 5 years of their first episode of thrombosis.

The clinical diagnosis of DVT is suggested by symptoms of leg swelling, pain, tenderness on deep palpation, erythema, and pain on dorsiflexion of the foot (“Homan sign”). The accuracy of these clinical clues as independent indicators of DVT, however, is widely accepted to be in the vicinity of only 50%. Assessment of patient risk factors improves the positive predictive value of the physical examination and serologic tests for DVT ( Table 16-2 ). Many other common conditions can cause symptoms similar to acute DVT, such as heart failure, trauma, chronic venous insufficiency, and cellulitis. For these reasons, further diagnostic evaluation is necessary to establish the diagnosis.

Lower-extremity arterial insufficiency due to extensive DVT is a rare complication that can present in two forms ( Table 16-3 ). Phlegmasia alba dolens, in which the limb is swollen, pale, with diminished pulses, is transient and believed to be due to arterial spasm in response to acute iliofemoral thrombosis. Phlegmasia cerulea dolens is characterized by sustained cyanosis, edema, and arterial insufficiency ( Fig. 16-12 ). The mechanism of ischemia in these patients is arterial collapse due to massive tense edema in the presence of extensive venous thrombosis: in essence compartment syndrome involving the entire limb. Mortality rate is high (almost 25%), and venous gangrene and amputation complicates more than 25% of cases.

Measurement of serum fibrin D-dimer, a degradation product of fibrinolysis, can be used as an initial screening test for the presence of thrombus in patients with low risk for DVT. A normal D-dimer level (<500 μg/L) has greater than 95% sensitivity in this patient population. This test is less sensitive in hospitalized patients, those considered high risk, age older than 65 years, and pregnant women.

Imaging remains essential in the diagnosis of DVT. The most widely applied imaging modality for detection of lower-extremity DVT is ultrasound ( Box 16-2 ). A noncompressible vein is the single most reliable criteria for the presence of thrombus, as long as the examination is adequate (see Fig. 16-8 ). The sensitivity and specificity for ultrasound are both greater than 95% for detection of thrombus in the popliteal vein and above in patients with symptoms of DVT. The sensitivity and specificity are both closer to 80% for calf DVT in asymptomatic patients. Small thrombi, particularly those limited to valve cusps or perforating veins, are easily missed by ultrasound. Great care must be taken to ensure that duplicated femoral or popliteal veins are not overlooked by ultrasound, because thrombus in one moiety of a duplicated vein segment can occur. Venous ultrasound for DVT is relatively inexpensive, with little risk, high sensitivity and specificity, and wide availability. As a result, both the threshold for ordering the study and the overall positive rates are low.