Standards of the Polish Ultrasound Society - update. Sonography of the lower extremity veins.

This article has been prepared on the basis of the Ultrasonography Standards of the Polish Ultrasound Society (2011) and updated based on the latest findings and reports. Ultrasound examination of the lower extremity veins is relatively easy and commonly used to confirm or rule out venous thrombosis. However, a relatively easy compression test frequently requires experience, particularly in situations when imaging is difficult (due to lymphedema, dressing or thick tissues). The technique is time-consuming and requires assessment of each deep vein every 1 cm. Lesions in the deep veins cannot be ruled out when the vessels are assessed in only 2-3 points - a full examination is needed. The value of the method is the highest when the proximal section is assessed and the lowest when crural veins are evaluated. Doppler sonography is the basic method used when patients are prepared for a surgery of varicose veins. The assessment of the superficial veins prior to this procedure is tedious and requires knowledge of anatomy together with numerous variants. A considerable challenge is posed by re-assessment of recurrent varicose veins following a previous surgery. The Standards include anatomic nomenclature proposed by the Polish Society for Vascular Surgery and Polish Society of Phlebology, which should facilitate communication with clinicians. The most beneficial patient positions have been thoroughly discussed in terms of safety and effectiveness of the examination. Sometimes during such an examination, no venous pathology is found, but other changes with symptoms that suggest deep thrombophlebitis are detected. In such a situation, it is necessary to conduct an initial (or complete, if possible) assessment of lesions as well as provide recommendations connected with further, more detailed diagnosis.

Introduction

Gray-scale sonography (2D) in combination with color imaging (color Doppler) and spectral registration (PW Doppler) is still the basic technique in assessing lesions in every vascular bed.

The diagnosis of venous thrombosis in the lower extremities as well as preparation of patients for procedures to treat varicose veins of the lower limbs is based on ultrasound imaging. Phlebography is reserved for particularly difficult or doubtful cases.

Equipment

The ultrasound scanner must be equipped with the pulsed and color Doppler options with electronic ultrasound beam steering. The size of the Doppler sampling gate should also be adjustable. Duplex and triplex options, which enable assessment of flow spectrum and/or filling of the vessel with color in real time as the transducer moves, are also needed.

To exam peripheral venous vessels we use the transducers of 5 MHz, 7.5 MHz or broadband transducers with the frequency of 4–7 MHz or 5–10 MHz. Broadband probes with higher f requency range (5–12 MHz) can also be used, but thickness of tissues may limit their usage due to lower penetration of the ultrasound beam. The front of the transducer should be approximately 35–50 mm long, which enables its free movement. Convex 3.5 MHz transducers are used for the assessment of the iliac veins and inferior vena cava.

The US system must have the option of ultrasound beam steering, which is essential to obtain the image of blood flow in color and to record the spectrum of flow. The optimal inclination angle is approximately 20°. The dynamic range of the electronics should be as high as possible to get proper imaging when tissues are thick or lymphedema is present, i.e. when morphological assessment of the vessels is more difficult. The following are also recommended:

measurement software;

system for image archiving (videoprinter, HDD, DVD, USB port).

Selection of transducers:

An examination of the veins in the extremities should be performed with a linear transducer (venous preset should be selected). The veins in the abdominal cavity should be assessed with a convex probe (abdominal preset; adjusting settings depending on the image obtained).

Focus settings:

The focus should be at the level of or slightly above the examined site.

Image enhancement and dynamics settings:

The dynamics range in 2D examinations of vessels is lower than in general examinations (at the level of 45–55 dB). In normal conditions, this renders the lumen anechoic.

Spectrum registration settings:

The venous preset should be selected and the velocity range as well as the velocity of spectrum registration should be modified, if needed.

Color settings:

The venous preset should be selected and the velocity range should be modified, if needed (lower values should be selected).

One should also remember about the Wall Filter settings. This filter removes the frequencies (velocities) from Doppler trace according to the examiner's choice. When set to higher frequencies, it may remove lower velocities that are frequently seen in venous flow.

Preparation for examination

A part of the examination involves assessment of the abdominal vessels; therefore the patient should not eat for at least 6–8 hours prior to the examination or should have only a very light meal. This is essential when the iliac veins and inferior vena cava are assessed.

Anatomy

We observe a considerable individual variability in terms of the number and course of the superficial veins. In the calf, the number of the deep veins that accompany arteries is also variable. The complete description of the current nomenclature can be found in the standards of the Polish Society for Vascular Surgery and Polish Society of Phlebology(.

The deep veins are divided into three sections:

iliac section (inferior vena cava and common, internal and external iliac veins);

proximal section (common femoral vein, deep femoral vein, femoral vein and popliteal vein);

distal section (posterior and anterior tibial veins, fibular veins and intramuscular veins).

Superficial veins:

Great saphenous vein (GSV) – its diameter reaches 8.8 mm in the inguinal region and in the calf – 3–5 mm. It runs from the groin down to the medial malleolus. The localization of its drainage to the common femoral vein at the level of the groin (the sapheno-femoral junction) is significant. The vein should run between two fasciae in the saphenous opening. The external pudendal vein, superficial epigastric vein and superficial circumflex iliac vein are also visible in the inguinal region. The great saphenous vein in the inguinal region devides into the accessory anterior and accesory posterior saphenous vein (this accessory posterior vein may run to the calf as the Leonardo's vein or posterior arch vein).

Small saphenous vein (SSV) – its diameter is approximately 4 mm. In the popliteal fossa, it presents one of three draining forms:

the vein usually communicates with the popliteal vein;

it runs to the thigh as a femoral extension of the SSV or as the Giacomini vein and drains in the popliteal vein;

it does not communicate with the popliteal vein.

At the calf, it gives off typical branches and a perforator to the medial head of the gastrocnemius muscle. It may communicate with the great saphenous vein via one or two branches.

Perforator veins – their number is difficult to determine. It is proposed that no names should be used to describe perforators. It is best to provide their localization in centimeters above the sole of the foot, and if measurements cannot be performed, they should be described less precisely as 1/3 of the distal, 1/3 of the medial and 1/3 of the proximal calf.

Scanning technique

Morphological evaluation of the veins

During the examination, it is essential to trace all venous sections on their entire length. Each vessel is assessed morphologically in a 2D image in a transverse or, if needed, longitudinal views. The examination involves assessment of echogenicity of the lumen (presence of fibrosis, clots, rulonisation effect). Ultrasound compression test should be performed.

Ultrasound compression test

The ultrasound compression test is used for assessment of thrombi (fibrosis) in the deep and superficial veins. It is the basic method to diagnose thrombosis (fig. 1)(. When performing the compression test, the following must be remembered:

Fig. 1A

Ultrasound compression test. Popliteal vein – 7.3 mm prior to compression and 5.3 mm following compression

the venous vessel must be positioned centrally in the field of view of the ultrasound probe;

focusing should be set at the level of the examined vessel;

compression should be applied until complete collapsing and subsequently, the pressure should be released;

we should move by 1 cm peripherally and apply repeated compression until complete collapsing;

compression should not be applied when free-floating thrombus is detected – color options should be applied to confirm its presence.

Ultrasound compression test. Small saphenous vein – 5.4 mm prior to compression and 2.9 mm following compression

Attention should be directed to the echogenicity of clots – low echogenicity means recent thrombosis.

Assessment of vessels using the color mode

Color can be applied as a technique that facilitates assessment of the lumen only in some situations. It indicates the direction of blood flow and therefore may be an additional technique to visualize reflux. Nevertheless, measurement of retrograde flow duration on the spectrum remains the standard technique.

Spectrum of blood flow and reflux duration measurement

The spectrum is recorded by placing the transducer longitudinally along the vessel. The Doppler gate should be set centrally in the lumen of the vessel.

In the region of the femoral veins, reflux should be assessed with the patient in a supine position with the use of the Valsalva maneuver (peripheral massage is relatively unreliable). Peripheral massage should be applied in the upright position.

In the case of the popliteal vein, peripheral massage should be used (vertical/sitting position).

In the case of the great saphenous vein, one should perform peripheral massage and Valsalva maneuver, and in the small saphenous vein – peripheral massage should be conducted (vertical/sitting position).

In Anglo-Saxon textbooks, the usage of inflatable compression sleeves is recommended as the most objective and comparable method to enhance blood flow (when the sleeve is placed below the examined level) or to elicit retrograde reflux (when the sleeve is placed above the examined level). The sleeve is inflated in approximately 3 seconds and emptied in 0.3 seconds.

Reflux duration evaluation

The normal values proposed by Labropoulos( are presented in tab. 1. Larger veins have fewer valves, therefore the expected closure time is longer than in smaller veins.

Tab. 1

Normal values proposed by Labropoulos(

In the common femoral vein, femoral vein and popliteal vein	1000 ms
In the superficial veins, deep femoral vein, crural veins and intramuscular veins	<500 ms
Perforators	<350 ms

The standard according to the recommendations of the Polish Society for Vascular Surgery and Polish Society of Phlebology( is presented in tab. 2. Reflux can be diagnosed when retrograde flow duration exceeds 0.5 seconds.

Tab. 2

Reflux duration according to the recommendations of the Polish Society for Vascular Surgery and Polish Society of Phlebology. It is not dependent on the vascular bed

Reflux duration

>0,5 s

It occurs that the best solution is to provide an absolute value of reflux duration – so that the clinician can interpret the results according to the norms that he or she uses (fig. 2).

Fig. 2

Reflux duration measurement – 1.24 s

How to position the patient? Examination tactics

A venous ultrasound examination is performed for various reasons (e.g. suspicion of thrombosis, assessment of varicose veins, differential diagnosis of edema or pain in the extremities etc.). Irrespective of the purpose of the examination, the first basic problem is ruling out thrombotic/ post-thrombotic lesions in the deep veins. The presence of such lesions considerably limits the surgeon who intends to treat varicose veins in surgery. In fact, it prevents his or her actions. In order to rule out these lesions, one should assess: the iliac veins in the abdominal cavity, the veins in the thigh (common femoral, deep femoral and femoral vein) and the calf veins (popliteal, intramuscular, tibial and fibular veins). The iliac veins cannot be examined in the upright position.The deep calf veins must be well filled with blood to be examined (i.e. the patient must remain in a vertical position – sitting or standing). The veins in the thigh can be assessed with the patient in a supine position or standing (which is slightly less favorable). When standing, patients involuntarily tighten their muscles, even in the extremity on which they do not support (the examined extremity should be relaxed). This may result in insufficient filling of the veins in the muscles thereby preventing thorough evaluation for which relaxed muscles are needed.

Safety of the patient is a significant aspect. The patient may not be able to stand without movement for 20–30 minutes. This problem is eliminated in the sitting position with lowered extremities. The assessment of varicose veins is always performed in a vertical position. The sitting position with lowered extremities is a vertical position – varicose veins do not disappear in this position. If there are doubts regarding the assessment of the superficial vessels, it is always possible to change the position to standing for a while.

The physician should decide about the standing or sitting position of the patient based on their condition, age, cooperation etc.( The authors suggest the following positions for given cases:

deep calf veins – sitting position with lowered crus or standing position (which is preferred in the assessment of the superficial veins);

valve sufficiency assessment – vertical position, but if it is uncertain whether the patient is able to stand – the sitting position.

The textbook entitled The Vascular System ( recommends as follows:

examining the deep veins – the reverse Trendelenburg position (supine position with elevated head and torso);

examining the superficial veins – standing or sitting position with lowered legs (sitting when: there are evident varicose veins and reflux, patient may collapse, feels dizzy or experiences discomfort while standing, or when the patient is disabled to a certain degree).

The above mentioned indications suggest that the physician should decide about the way of the examination to enable assessment of all essential elements in a safe way.

A significant element of the examination is the presence of a platform or a bed with adjustable height. The platform should have handrails for the stability of the patient.

Range of the examination to diagnose thrombosis

Numerous authors suggest that the examination should always be performed in both extremities. However, it is admissible to examine only one symptomatic extremity. A complete examination consists of several stages:

The first stage involves the examination of the inferior vena cava and iliac veins in terms of thrombosis. The assessment is conducted in a supine position with the use of a convex probe with the frequency of 3.5 MHz. Following morphological visualization of t he vessels in 2D, we use color a nd a ssess t he degree to which it fills the vessels. The velocity scale (10 cm/s for the iliac veins) and enhancement should be selected adequately (color cannot go beyond the wall of the vessel).

The next stage involves assessment of the deep veins in the lower extremities in terms of thrombosis. The examination of the femoral section is performed with the patient in supine position with abduction and slight rotation of the examined extremity. The sufficiency of the femoral veins should be assessed.

In order to examine the calf, the patient should be placed in a sitting position, or when they cannot sit, it can be attempted to lower the crus beyond the bed so that blood could also fill the intramuscular veins. The examination of the femoral and calf sections in the upright position does not usually allow proper compression test to be conducted every 1 cm in all vessels. Moreover, the deep vessels of the thigh are not as easily accessed.

The sufficiency of the popliteal vein should be evaluated.

The next stage involves assessment of the superficial veins in terms of the presence of thrombi. The examination is performed in the sitting position, and when there are doubts concerning the lesions detected or when the patient can stand safely with no risk of collapsing – in the standing position.

The sufficiency of the valves of the femoral and popliteal veins as well as the main trunks of the superficial veins should be assessed (when there is no thrombosis). If varicose veins are present, their localization, origin of supply and the presence of thrombi should be described. It is also important to assess the patency of the perforators. A more detailed examination of varicose veins is not necessary in this situation.

Range of examination prior to varicose vein surgery

In order to thoroughly assess varicose veins and perform certain measurements (e.g. perforator sufficiency), assistance of another person is frequently necessary.

The preparation of the patient for a procedure requires ruling out lesions in the deep veins and detailed description of lesions in the superficial veins. Numerous authors suggest that the examination should always be performed in both extremities. However, it is admissible to examine only the extremity that is being prepared for the procedure.

The stages 1, 2 and 3 are the same as in examining the patient to diagnose thrombosis. An essential element of superficial vein examination is assessment of anatomic types of the great and small saphenous veins.

4. Assessment of the superficial veins

Great saphenous vein (GSV) – its diameter in the inguinal region, thigh and calf should be measured. In the thigh, the following should be assessed: sufficiency of the drainage to the common femoral vein and sufficiency of the peripheral section. In the calf, we should also assess sufficiency at two levels (proximal and distal level). The results should include the range of reflux. It is important to describe the anatomy of the great saphenous vein and its femoral branches. Dilated branches and their junctions ought to be described.

Small saphenous vein (SSV) – we should describe the type of drainage in the popliteal fossa. Its sufficiency should be assessed and the range of reflux should be noted, if applicable.

Perforators – we should describe the localization of the visualized perforators in the thigh and calf. The best way to describe their localization in the calf is to provide their distance from sole of the foot in centimeters. A less precise manner is the division into: 1/3 of the distal, 1/3 of the medial and 1/3 of the proximal crus. We should also assess the sufficiency of the perforators (reflux duration) and measure their diameters (the diameter does not unequivocally determine sufficiency, but when it is >4 mm – insufficiency is highly probable)(.

Others – we should also assess the range and type of other lesions in the subcutaneous tissue. Attention should be paid to pathologies that might mimic venous thrombosis (lymphedema of the subcutaneous tissue, cysts, muscle tears, hematoma etc.).

Report

The results should include two elements: description and photographic documentation. The photographic documentation should include the name and surname of the patient, their age, date of the examination and name of the laboratory. The description must include these data as well as the details of the examining physician. Moreover, the name of the scanner and type of the probe used should also be mentioned. In order to make the description clear, it is recommended to:

include separate descriptions of the deep and superficial veins;

include separate descriptions of the superficial veins of the left and right extremity if lesions are present.

Even if the result is normal, the description should mention the vessels examined and information concerning their condition (normal/altered). If thrombosis is diagnosed, the localization and range of lesions should be thoroughly described. A good habit is to measure the diameter of affected veins prior to and following compression, which allows dynamics of lesions to be assessed in the course of several subsequent scans. Moreover, it should be attempted to estimate the age of thrombi based on echogenicity.

The description of varicose veins should include details concerning sufficiency/insufficiency of the valves and the range of this phenomenon in the great and small saphenous veins. Moreover, perforators should be described as well – as has been mentioned above.

Other changes detected during the examination (lymphedema of the subcutaneous tissue, cysts, muscle tears, hematoma etc.) should also be included.

The result should end with a conclusion in which the pathologies detected are summarized together with recommendations concerning further follow-up and consultation. In the case of recent thrombosis, it is essential to urgently refer the patient to a clinician who will be able to implement treatment.