Current diagnosis and management of chronic venous disease (CVD) is predominantly based on identification and correction of two hemodynamic abnormalities : obstruction of the venous flow and venous reflux . In primary CVD, reflux is the only identifiable hemodynamic abnormality, while in the secondary CVD (postthrombotic disease), reflux can be present as the sole finding or in combination with obstruction or it can be absent.

Venous reflux is a hemodynamic phenomenon of reversal of the venous flow. Unidirectionality of the blood flow in veins is secured by function of competent venous valves. This frequently leads to misconception that the presence of reflux indicates valvular incompetence. Some venous segments may have reversed flow without valvular incompetence, for example, a venous segment between two competent valves with two or more tributaries joining it and a competent perforator vein. The flow in this segment sometimes is directed from the tributaries through the segment into the perforator vein. Thus, measuring the flow in this segment results in the detection of reversed flow, which is a reflux, but does not indicate that any of the valves are incompetent. The absence of reflux also does not mean that the valves are competent. Proximal venous obstruction or overload of more distal venous segments results in the absence of reversed flow regardless of the venous valve competency. Current clinical diagnostic testing, however, is unable to directly examine the function of venous valve, and the detection of reflux remains the only indirect indication of abnormal function of venous valves.

Reflux can be detected during ultrasound examination without performing any special maneuvers. However, this happens rarely and cannot be quantified or judged if this is a pathological sign. The standard methodology for reflux detection involves reflux-provoking maneuvers such as Valsalva and distal compression-decompression . Valsalva maneuver increases abdominal pressure creating reverse pressure gradient in the veins. This, however, is mostly limited to venous segments in the proximal lower extremity where the valves are absent common femoral vein (CFV) or incompetent. Since there is no emptying of the more distal venous segments prior to performing Valsalva maneuver , their filling with blood may obstruct the ability to detect reflux. Emptying of the venous segments by compression of the segment of the leg distal to the visualized venous segment, followed by a rapid release of the pressure, is the most reliable way to induce venous reflux. This can be done by using operator’s hand—or in a more standard fashion, using a pneumatic cuff with a rapid compression-relief device.

Most institutions prefer examining patient in a standing position with the weight of the patient on the contralateral leg. The extremity that is examined is slightly bended in the knee and rotated externally, allowing examination of the entire venous system from the CFV to the veins of the ankle. It has been shown that such position results in more repeatable results [27]. In practice, examining a standing patient is not always possible or desirable. Many patients are unable to stand for the time of the test, and performing the test in this way requires additional equipment or introduces substantial challenges to the ultrasonographer. Performing the study in the reversed Trendelenburg position generates almost identical results and is much more practical [28].

Examining perforating veins (PVs) requires slightly different technique. Thigh PVs can be examined in either standing or reversed Trendelenburg positions, but calf PVs are better seen in patient sitting with legs hanging off the examining table. Ultrasound transducer should be in transverse or oblique plane which is parallel to IP axis. Most of the clinically relevant PVs are located close to the GSV and SSV, so scanning along these vessels and their tributaries is the most efficient way to identify incompetent perforators.

Proper identification of reflux requires real-time duplex or triplex examination . This means that the spectrum Doppler recordings should be performed simultaneously with imaging (B-mode with or without color Doppler). Any other technique introduces uncertainty of which vessel was insonated during reflux-provoking maneuver . These maneuvers result in movements of all anatomical structures, veins including, making possible movement of artifacts and insonation of a tributary, adjoin vessel, or nonvascular structure, increasing false-negative and false-positive findings.

Definition of pathological reflux is consensus-based but is universally accepted around the world. It is based on the time of the reversed flow, and commonly used cut-off points are 1 s and 0.5 s for truncal veins. A multicenter study that most rigorously examined factors influencing reliability of reflux measurements demonstrated that using 0.5 s value has advantage for both superficial and deep veins [27]; however, some laboratories are using different criteria for deep and superficial veins based on their clinical experience and beliefs. The same study demonstrated that the time of the ultrasound examination introduces the highest variability of the measurements. The likelihood of getting different results of the repeated test in the same patient (presence vs. absence of reflux) is much higher when patient is examined at different time of the day than if he was examined in different positions and using different provoking maneuvers.

PVs have a different definition of pathological reflux, which is based on the reflux time (>0.5 s), diameter (≥3.5 mm), and a location beneath open or healed ulcer [29].

Upper extremity venous compression syndromes such as venous thoracic outlet syndrome (VTOS) often require additional imaging for conformation. Venous thoracic outlet disease is sometimes also referred to as thoracic inlet syndrome. Thrombosis of the upper extremity veins can be ruled out with a standard scanning protocol (as outlined above), but in the absence of “effort” thrombosis (Paget-von Schroetter syndrome ) which can be a presenting feature of VTOS, other maneuvers may be indicated to confirm a suspected diagnosis. In addition to color Doppler and spectral waveform analysis in the neutral position, the patient is subjected to a variety of maneuvers including arm abduction at 45°, 90°, and 120°, the so-called military position (chest thrust forward with shoulders rolled back), and the Adson maneuver which tests the role of compression from the scalene muscles on the structures of the thoracic outlet (subclavian vein, subclavian artery, and the upper and lower brachial plexuses) by rotating the head toward the affected side and taking a deep inspiration (Fig. 3.3). The radial pulse can simultaneously be assessed for dropout while performing the Adson maneuver to assess concurrently for arterial compression. A positive study with TOS maneuvers will demonstrate loss of pulsatile or respirophasic flow with monophasic characteristics or complete obliteration of flow. Simultaneous duplex assessment of the subclavian artery during the maneuvers may be requested as well since arterial and venous compression may coexist. CT, MR, and conventional venography are rarely necessary for the diagnosis of VTOS but may assist with evaluating for the anatomic cause of thoracic outlet compression when surgical corrective measures are considered.

Venous compression involving the lower extremities usually manifests in the pelvic region in the form of May-Thurner syndrome or rarely at the knee as a type 5 popliteal entrapment syndrome . May-Thurner compression, classically defined as compression from the right common iliac artery onto the left common iliac vein as the vein passes anterior to the lumbar spine, has increasingly been appreciated to be present in cases of left iliofemoral DVT. Atypical May-Thurner iliac vein compression has also been described, which can involve the right common iliac vein as well. Diagnostic imaging for all types of suspected iliac vein obstruction usually begins with lower extremity venous duplex images, which should be carried as proximal into the iliac region as the habitus of the patient will allow. Blunted signals with respiration and augmentation in Doppler flow analysis will serve as clues for proximal obstruction. Thrombosis is not uncommonly encountered extending to or beyond the proximal lower extremity veins. CT venography is most commonly employed to assess the compression and degree of any associated thrombosis since venous ultrasound is not always reliable in the pelvic region. Involvement of the IVC can also be ascertained with either CT or MR venography.

Popliteal artery entrapment is a rare entity, which uncommonly can involve significant venous compression as well. This is referred to as a type 5 compression, which will often involve both the vein and artery. Ultrasound can be used as an initial diagnostic tool in the popliteal fossa with both passive and active dorsiflexion of the ankle. Blunted phasic Doppler waveforms or loss of augmentation proximal to the popliteal vein with maneuvers can serve as a clue to the presence of compression. MR angiography is the imaging modality of choice to supplement physiologic testing when assessing for any type of popliteal entrapment in order to ascertain the exact anatomic subset of vascular compression.

Visceral venous compression is rare but has been described in the left renal vein when it is compressed by the superior mesenteric artery and the aorta. This is referred to as the Nutcracker syndrome and can cause renal venous hypertension leading to hematuria and flank pain or gonadal pain. The gold standard for imaging has classically been left renal venography, but CT venography is now used routinely as an initial assessment given the additional anatomic information it provides and the often wide differential that is entertained when patients present with flank or gonadal pain associated with hematuria.

Imaging for vascular malformations needs to be tailored to the region and the type of malformation that is suspected. Arteriovenous fistulas) are most frequently acquired, usually as a minor complication following a percutaneous procedure. Given the relative superficial location with high flow, ultrasound is usually best suited for evaluation, especially in the inguinal areas. The typical ultrasound finding is a high flow “jet” connecting an artery to a vein with arterialized flow in the vein immediately proximal to the fistula (Fig. 3.4). This is in distinction to the “to-fro” flow leading from an artery to a blind-ended cavity with pseudoaneurysms (Fig. 3.5). Other types of vascular malformation sometimes present diagnostic challenges, especially when they are small with low flow. Venous malformations can appear as low flow areas of phlebectasia, disorganized aneurysm, or spongiform hypoechoic mass. Lymphatic malformations , on the other hand, often appear cystic on ultrasound. MR venography is often useful when there are multiple suspected venous malformations such as in Klippel-Trenaunay syndrome . Findings on MRI include uniform enhancement around venous structures versus rim or septal enhancement of cyst walls and high T2 signal intensity that is typical for lymphatic malformations. The presence of signal voids provides a clue to the presence of phleboliths characteristic of venous malformations. Finally, conventional venography is often the gold standard for both imaging the associated deep and superficial components of a venous malformation. This often precedes endovascular treatment with sclerosing) or occluding agents or devices for definitive treatment of problematic venous malformations.

Contrast venography is almost completely replaced by duplex ultrasound as an initial test for diagnosing DVT; however, it continues to be the main tool for invasive treatment of deep veins. It is expensive and inconvenient compared with other diagnostic modalities and potentially causes patient discomfort and complications [30, 31]. Direct comparison of diagnostic accuracy of Duplex ultrasound and contrast venography demonstrated a sensitivity and specificity of 96% and 91%, respectively, for contrast venography and 78% and 97% for duplex ultrasonography [32, 33], suggesting that venography still has a place as a backup test for patients with suspected DVT and negative ultrasound [34]. In practice, however, immediate anticoagulation is a better strategy for such patients, and justification for performing an invasive test is questionable in majority of the cases .