Ultrasound diagnosis of venous thrombosis. Scientific review

Acute venous thrombosis is a common and dangerous disease. According to statistics, its frequency in the general population is about 160 per 100,000 population. Thrombosis in the inferior vena cava (IVC) system is the most common and dangerous type of this pathological process and is the main source of pulmonary embolism (84.5%). The superior vena cava system accounts for 0.4-0.7% of pulmonary embolisms (PE), the right side of the heart - 10.4%. Thrombosis of the veins of the lower extremities accounts for up to 95% of cases of all thrombosis in the IVC system. The diagnosis of acute venous thrombosis is diagnosed intravitally in 19.2% of patients. In the long term, deep vein thrombosis (DVT) leads to the formation of postthrombophlebitic disease, manifested by chronic venous insufficiency up to the development of trophic ulcers, which significantly reduces the ability to work and the quality of life of patients.

The main mechanisms of intravascular thrombus formation, known since the time of R. Virchow, are slowing of blood flow (stasis), hypercoagulation, injury to the vessel wall (endothelial damage). Acute venous thrombosis quite often develops against the background of various oncological diseases (malignant tumors of the gastrointestinal tract, female genital area, etc.) due to the fact that cancer intoxication causes the development of hypercoagulable changes and inhibition of fibrinolysis, as well as due to mechanical compression of the veins by the tumor and germination it into the vascular wall. Predisposing factors for DVT are also considered obesity, pregnancy, taking oral hormonal contraceptives, hereditary thrombophilias (deficiency of antithrombin III, protein C and S, Leiden mutation, etc.), systemic connective tissue diseases, chronic purulent infections, allergic reactions. Elderly and senile patients and persons suffering from chronic venous insufficiency of the lower extremities, as well as patients with myocardial infarction, decompensated heart failure, stroke, bedsores, and gangrene of the lower extremities are at the greatest risk of developing DVT. Trauma patients are of particular concern, since femoral fractures are mainly found in elderly and senile people, most burdened by somatic diseases. Thrombosis in trauma patients can occur with any injury to the lower extremities, since all etiological factors of thrombosis (vascular damage, venous stagnation and changes in blood coagulation properties) occur.

Reliable diagnosis of phlebothrombosis is one of the current clinical problems. Physical examination methods make it possible to make a correct diagnosis only in typical cases of the disease, and the frequency of diagnostic errors reaches 50%. For example, thrombosis of the veins of the calf muscles with preserved patency of the remaining veins is often asymptomatic. Because of the danger of missing acute DVT of the legs, clinicians often make this diagnosis in every case of pain in the calf muscles. Particular attention should be paid to “trauma” patients, in whom the presence of pain, swelling and discoloration of the limb may be a consequence of the injury itself, and not of DVT. Sometimes the first and only manifestation of such thrombosis is massive pulmonary embolism.

The tasks of instrumental examination include not only confirming or refuting the presence of a thrombus, but also determining its extent and degree of embologenicity. Isolating embolic-dangerous thrombi into a separate group and studying their morphological structure are of great practical importance, since without this it is impossible to develop effective prevention of pulmonary embolism and select optimal treatment tactics. Thromboembolic complications are more often observed in the presence of a floating thrombus with a heterogeneous structure and an uneven hypo- or isoechoic contour, in contrast to thrombi that have a hyperechoic contour and a homogeneous structure. An important criterion for the embologenicity of a thrombus is the degree of its mobility in the lumen of the vessel. Embolic complications are more often observed with severe and moderate mobility of thrombomass.

Venous thrombosis is a fairly dynamic process. Over time, the processes of retraction, humoral and cellular lysis help reduce the size of the thrombus. At the same time, processes of its organization and recanalization are underway. In most cases, vascular patency is gradually restored, the valve apparatus of the veins is destroyed, and the remains of blood clots in the form of wall overlays deform the vascular wall. Difficulties in diagnosis may arise when repeated acute thrombosis occurs against the background of partially recanalized veins in patients with postthrombophlebitic disease. In this case, a fairly reliable criterion is the difference in vein diameter: in patients with signs of recanalization of thrombus masses, the vein diameter decreases due to the subsidence of the acute process; with the development of rethrombosis, there is again a significant increase in the diameter of the vein with unclear (“blurred”) contours of the walls and surrounding tissues. The same criteria are used in the differential diagnosis of acute parietal thrombosis with postthrombotic changes in the veins.

Of all the non-invasive methods used to diagnose thrombosis, ultrasound scanning of the venous system has recently been increasingly used. The triplex angioscanning method, proposed by Barber in 1974, includes the study of blood vessels in B-mode, analysis of the Doppler frequency shift in the form of classical spectral analysis and flow (in speed and energy modes). The use of spectral technology made it possible to accurately measure blood flow inside the lumen of the veins. The use of method () made it possible to quickly distinguish occlusive from non-occlusive thrombosis, identify the initial stages of recanalization of thrombi, and also determine the location and size of venous collaterals. In dynamic studies, the ultrasound method allows for fairly accurate monitoring of the effectiveness of thrombolytic therapy. In addition, with the help of ultrasound, it is possible to determine the causes of clinical symptoms similar to those in venous pathology, for example, to identify a Baker's cyst, intermuscular hematoma or tumor. The introduction into practice of expert-class ultrasonic devices with sensors with frequencies from 2.5 to 14 MHz made it possible to achieve almost 99% diagnostic accuracy.

Material and methods

The examination included examination of patients with clinical signs of venous thrombosis and pulmonary embolism. Patients complained of swelling and pain in the lower (upper) limb, pain in the calf muscle (usually of a bursting nature), “pulling” pain in the popliteal region, pain and compaction along the saphenous veins. Upon examination, moderate cyanosis of the leg and foot, dense swelling, pain on palpation of the leg muscles were revealed; in most patients, positive Homans and Moses symptoms.

All subjects underwent triplex scanning of the venous system using modern ultrasound machines with a linear sensor with a frequency of 7 MHz. At the same time, the condition of the veins of the thigh, popliteal vein, veins of the leg, as well as the great and small saphenous veins was assessed. A 3.5 MHz convex probe was used to visualize the iliac veins and IVC. When scanning the IVC, iliac vein, great saphenous vein, femoral veins and veins of the leg in the distal lower extremities, the patient was in the supine position. The study of the popliteal veins, veins of the upper third of the leg and the small saphenous vein was carried out with the patient lying on his stomach with a cushion placed under the ankle joints. Difficulties in diagnosis arose when visualizing the distal part of the superficial femoral vein in obese patients, visualizing the veins of the leg with pronounced trophic and indural changes in tissue. In these cases, a convex sensor was also used. Scanning depth, echo signal amplification and other study parameters were selected individually for each patient and remained unchanged during the entire examination, including observations over time.

The scan was started in cross-section to exclude the presence of a floating tip of the thrombus, as evidenced by complete contact of the venous walls during light compression with the sensor. After making sure that there was no freely floating tip of the thrombus, a compression test with a sensor was carried out from segment to segment, from proximal to distal sections. The proposed method is the most accurate not only for detecting thrombosis, but also for determining its extent (excluding the iliac veins and IVC, where the patency of the veins was determined in the CD mode). veins confirmed the presence and characteristics of venous thrombosis. In addition, longitudinal sectioning was used to locate the anatomical venous confluence. During the examination, the condition of the walls, the lumen of the veins, the localization of the thrombus, its extent, and the degree of fixation to the vascular wall were assessed.

Ultrasonic characterization of venous thrombi was carried out in relation to the lumen of the vessel: they were distinguished as parietal, occlusive and floating thrombi. Signs of parietal thrombosis were considered to be visualization of a thrombus with the presence of free blood flow in the lumen of the vein, the absence of complete collapse of the walls when the vein is compressed by a sensor, the presence of a filling defect during color circulation, and the presence of spontaneous blood flow during spectral Dopplerography (Fig. 1).

Rice. 1. Non-occlusive thrombosis of the popliteal vein. Longitudinal scanning of the vein. Envelope blood flow in energy flow coding mode.

Ultrasound criteria for floating thrombi were: visualization of the thrombus as an echogenic structure located in the lumen of the vein with the presence of free space, oscillatory movements of the apex of the thrombus, absence of contact of the vein walls during compression with the sensor, presence of free space when performing respiratory tests, circumflex type of blood flow during color circulation, the presence of spontaneous blood flow with spectral Doppler ultrasound. When a floating thrombus was detected, the degree of its mobility was assessed: pronounced - in the presence of spontaneous movements of the thrombus during quiet breathing and/or breath-holding; moderate - when oscillatory movements of a blood clot are detected during functional tests (cough test); insignificant - with minimal mobility of the thrombus in response to functional tests.

Research results

From 2003 to 2006, 236 patients aged from 20 to 78 years were examined, 214 of them with acute thrombosis and 22 with pulmonary embolism.

In the first group, in 82 (38.3%) cases, the patency of the deep and superficial veins was not impaired and clinical symptoms were due to other reasons (Table 1).

Table 1. Conditions with symptoms similar to DVT.

The diagnosis of thrombosis was confirmed in 132 (61.7%) patients, while in most cases (94%) thrombosis was detected in the IVC system. DVT was detected in 47% of cases, superficial veins - in 39%, damage to both the deep and superficial venous systems was observed in 14%, including 5 patients with involvement of perforating veins.

The probable causes (risk factors) of the development of venous thrombosis are presented in table. 2.

table 2. Risk factors for thrombosis.

In our observations, the most common form of thrombosis was detected, as well as damage to the veins at the level of the popliteal-tibial and femoral-popliteal segments (Table 3).

Table 3. Localization of DVT.

More often (63%) there were thromboses that completely occluded the lumen of the vessel; in second place in frequency (30.2%) were mural thrombi. Floating thrombi were diagnosed in 6.8% of cases: in 1 patient - in the saphenofemoral anastomosis with ascending thrombosis of the trunk of the great saphenous vein, in 1 - ileofemoral thrombosis with a floating apex in the common iliac vein, in 5 - in the common femoral vein with thrombosis of the femoral-popliteal vein segment and in 2 - in the popliteal vein with DVT of the leg.

The length of the non-fixed (floating) part of the thrombus, according to ultrasound data, varied from 2 to 8 cm. Moderate mobility of thrombotic masses was more often detected (5 patients), in 3 cases the mobility of the thrombus was minimal. In 1 patient, during quiet breathing, spontaneous movements of the thrombus in the lumen of the vessel were visualized (high degree of mobility). In our observations, floating thrombi with a heterogeneous echostructure were more often detected (7 people), with the hyperechoic component predominant in the distal section, and the hypoechoic component in the area of ​​the thrombus head (Fig. 2).

Rice. 2. Floating thrombus in the common femoral vein. B-mode, longitudinal scanning of the vein. Thrombus of a heteroechoic structure with a clear hyperechoic contour.

Over time, 82 patients were examined to assess the course of the thrombotic process, of which 63 (76.8%) had partial recanalization of thrombotic masses. In this group, 28 (44.4%) patients had a central type of recanalization (with longitudinal and transverse scanning in the color flow mode, the recanalization channel was visualized in the center of the vessel); in 23 (35%) patients, parietal recanalization of thrombotic masses was diagnosed (most often, blood flow was determined along the wall of the vein directly adjacent to the artery of the same name); In 13 (20.6%) patients, incomplete recanalization was detected with fragmentary asymmetric staining in the Color Doppler mode. Thrombotic occlusion of the vein lumen was observed in 5 (6.1%) patients; in 6 (7.3%) cases, restoration of the vein lumen was noted. Signs of rethrombosis persisted in 8 (9.8%) patients.

conclusions

A comprehensive ultrasound examination, including angioscanning using spectral, color and power Doppler modes and echography of soft tissues, is a highly informative and safe method that allows the most reliable and quick solution to issues of differential diagnosis and treatment tactics in outpatient phlebological practice. It is advisable to conduct this study on an outpatient basis for earlier identification of patients for whom thrombolytic therapy is not indicated (and sometimes contraindicated), and to refer them to specialized departments; when confirming the presence of venous thrombosis, it is necessary to identify individuals at high risk of developing thromboembolic complications; monitor the dynamics of the thrombotic process and thereby adjust treatment tactics.

Literature

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5. Savelyev V.S. Phlebology. M.: Medicine 2001; 664 pp.
6. Kokhan E.P., Zavarina I.K. Selected lectures on angiology. M.: Nauka 2000. P. 210, 218.
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Thrombotic damage to the venous bed of the lower extremities, primarily the deep veins, is an acute condition that develops as a result of the complex action of a number of factors. According to statistical reports from the Ministry of Health of the Russian Federation, 80,000 new cases of this disease are registered annually in our country. In elderly and senile age, the incidence of deep vein thrombosis increases several times. In Western European countries, this pathology occurs in 3.13% of the population. Venous thrombosis is the main cause of pulmonary embolism. Massive pulmonary embolism develops in 32-45% of patients with acute deep vein thrombosis of the lower extremities and ranks third in the overall structure of sudden mortality.

Deep vein thrombosis is the formation of a blood clot inside a vessel. When blood clots form, an obstruction to the outflow of blood occurs. Venous thrombosis can occur due to poor circulation (blood stagnation), damage to the inner wall of the vessel, increased ability of the blood to form a blood clot, or a combination of these reasons. The formation of a blood clot can begin in any part of the venous system, but most often in the deep veins of the leg.

Ultrasound compression duplex angioscanning is the main examination method for suspected venous thrombosis. The main tasks are to identify a blood clot, describe its density (this sign is important for diagnosing the duration of thrombosis), fixation to the walls of the vein, length, the presence of floating sections (capable of detachment from the vascular wall and moving with the blood flow), and the degree of obstruction.

Ultrasound examination also allows for dynamic monitoring of the state of the blood clot during treatment. An active search for deep vein thrombosis using duplex scanning seems appropriate in the preoperative period, as well as in cancer patients. The significance of ultrasound methods in the diagnosis of thrombosis is considered to be quite high: sensitivity ranges from 64-93%, and specificity - 83-95%.

Ultrasound examination of the veins of the lower extremities is carried out using linear sensors of 7 and 3.5 MHz. The study begins with the groin area in transverse and longitudinal sections in relation to the vascular bundle. The mandatory scope of the study includes examination of the subcutaneous and deep veins of both lower extremities. When obtaining an image of the veins, the following parameters are assessed: diameter, compressibility (compression by the sensor until blood flow in the vein stops while maintaining blood flow in the artery), features of the course of the vessel, the state of the internal lumen, the safety of the valve apparatus, changes in the walls, the condition of the surrounding tissues. The blood flow in the adjacent artery must be assessed. The state of venous hemodynamics is also assessed using special functional tests: respiratory and cough tests or straining tests (Valsalva maneuver). They are used primarily to assess the condition of the valves of the deep and saphenous veins. In addition, the use of functional tests facilitates the visualization and assessment of venous patency in areas of low blood flow. Some of the functional tests may be useful to clarify the proximal limit of venous thrombosis. The main signs of the presence of thrombosis include the presence of echo-positive thrombotic masses in the lumen of the vessel, the echo density of which increases as the age of the thrombus increases. In this case, the valve leaflets cease to differentiate, the transmitting arterial pulsation disappears, the diameter of the thrombosed vein increases by 2-2.5 times compared to the contralateral vessel, and during compression by the sensor it is not compressed.

There are 3 types of venous thrombosis: floating thrombosis, occlusive thrombosis, parietal (non-occlusive) thrombosis.

Occlusive thrombosis is characterized by complete fixation of thrombus masses to the venous stack, which prevents the transformation of the thrombus into an embolus. Signs of parietal thrombosis include the presence of a thrombus with free blood flow in the absence of complete collapse of the venous walls during a compression test. The criteria for a floating thrombus are visualization of the thrombus in the lumen of the vein with the presence of free space, oscillatory movements of the head of the thrombus, absence of contact of the vein walls during compression with the sensor, and the presence of free space when performing respiratory tests. To definitively determine the nature of the thrombus, a special Valsalva maneuver is used, which should be performed with caution due to additional flotation of the thrombus.

Ultrasound is the first-line diagnostic method for suspected deep vein thrombosis of the lower extremities. This is facilitated by the relatively low cost, availability and safety of the technique. At the Tambov Regional Clinical Hospital named after V.D. Babenko" ultrasound duplex angioscanning of peripheral veins has been carried out since 2010. About 2,000 studies are performed annually. High quality diagnostics allows saving the lives of a large number of people. Our institution is the only one in the region that has a vascular surgery department, which allows us to determine treatment tactics immediately after diagnosis. Highly qualified doctors successfully use modern methods of treating venous thrombosis.

E.A. MARUSHCHAK, Ph.D., A.R. ZUBAREV, Doctor of Medical Sciences, Professor, A.K. DEMIDOVA

Russian Research Medical University named after. N.I. Pirogov, Moscow

Methodology of ultrasound examination of venous thrombosis

The article presents four years of experience in performing ultrasound studies of venous blood flow (12,394 outpatient and inpatient patients with acute venous pathology of the Central Clinical Hospital of the Russian Academy of Sciences). Based on a large clinical material, the methodology for performing primary and dynamic ultrasound examinations in patients during the conservative treatment of venous thrombosis and when performing various methods of surgical prevention of pulmonary embolism is outlined. Particular attention is paid to the interpretation of ultrasound results in terms of the likelihood of pulmonary embolism. The results of application of the proposed ultrasound research methodology in the practice of a multidisciplinary emergency hospital and diagnostic and treatment center are analyzed.

Key words: ultrasound angioscanning, vein, acute venous thrombosis, deep vein thrombosis, pulmonary embolism, surgical prevention of pulmonary embolism

About Introduction

The epidemiology of acute venous thrombosis (AVT) is characterized by disappointing data: the incidence of this pathology in the world reaches 160 people per 100 thousand population annually, and in the Russian Federation - no less than 250 thousand people. According to M.T. Severinsen (2010) and L.M. Lapie1 (2012), the incidence of phlebothrombosis (PT) in Europe annually is 1:1000 and reaches 5:1000 in patients with skeletal trauma. A large-scale analysis of the incidence of deep vein thrombosis (DVT) conducted in the United States in 2012 showed that 300-600 thousand Americans are diagnosed with this pathology annually, and 60-100 thousand of them die from pulmonary embolism (PE). These indicators are due to the fact that OVT occurs in patients with a wide variety of pathologies and are often secondary, complicating any diseases or surgical interventions.

For example, the frequency of venous thromboembolic complications (VTEC) in inpatient (including surgical) patients reaches 10-40%. V.E. Barinov et al. cite data on the incidence of pulmonary embolism in air travelers, equal to 0.5-4.8 cases per 1 million passengers, with fatal pulmonary embolism causing 18% of deaths on airplanes and airports. PE is the cause of death in 5-10% of hospital patients, and this figure is steadily increasing. Massive and, as a consequence, lethal pulmonary embolism in some patients is the only, first and last manifestation of OVT. In a study by L.A. Laberko et al., devoted to the study of pulmonary embolism in surgical patients, provide data on mortality from VTEC in Europe: their number exceeds the total mortality from breast cancer, acquired immunodeficiency syndrome and car accidents and is more than 25 times higher than the mortality from infections caused by Staphylococcus aureus .

An interesting fact is that from 27 to 68% of all deaths from pulmonary embolism are potentially preventable. The high value of the ultrasound method in diagnosing OVT is due to its non-invasiveness and sensitivity and specificity approaching 100%. Physical methods of examining patients with suspected OVT make it possible to make a correct diagnosis only in typical cases of the disease, and the frequency of diagnostic errors reaches 50%. Thus, an ultrasound diagnostician has a 50/50 chance of verifying or excluding OVT.

Instrumental diagnosis of OVT is one of the urgent tasks in terms of visual assessment of the substrate of the disease, since the determination of angiosurgical tactics depends on the data obtained, and, if surgical prevention of pulmonary embolism is necessary, the choice of its method depends. Execution of dynamic

Ultrasound is necessary both during conservative treatment of OVT in order to assess emerging changes in the affected venous bed, and in the postoperative period.

Sonographers are at the forefront of visual assessment of OVT. Ultrasound is the method of choice in this category of patients, which dictates the need not only to detect OVT, but also to correctly describe and interpret all possible characteristics of this pathological condition. The purpose of this work was to standardize the methodology for performing ultrasound examination during OVT, aimed at minimizing possible diagnostic errors and maximizing adaptation to the needs of clinicians who determine treatment tactics.

About Materials

In the period from October 2011 to October 2015, 12,068 primary ultrasound scans of the blood flow of the inferior vena cava system and 326 of the superior vena cava system (12,394 ultrasound scans in total) were performed at the Central Clinical Hospital of the Russian Academy of Sciences (CDB RAS, Moscow). It is important to emphasize that the Central Clinical Hospital of the Russian Academy of Sciences does not purposefully accept acute venous pathology through the “ambulance” channel. Of the 12,394 studies, 3,181 were performed on outpatient patients of a diagnostic and treatment center, 9,213 on inpatient patients for suspected acute venous pathology or for prophylactic purposes in patients at risk for venous thromboembolic complications, as well as for indications as preoperative preparation. OVT were diagnosed in 652 inpatients (7%) and 86 outpatients (2.7%)

(total 738 people, or 6%). Of these, the localization of OVT in the bed of the inferior vena cava was detected in 706 (95%), in the bed of the superior vena cava - in 32 patients (5%). Vascular ultrasound was performed on the following devices: Voluson E8 Expert (GE HC, USA) using multi-frequency convex (2.0-5.5 MHz) and linear (5-13 MHz) sensors in the following modes: B-mode, color Doppler mapping, power Doppler mapping, pulsed wave mode and mode of sub-ppler blood flow imaging (B-flow); Logiq E9 Expert (GE HC, USA) with a similar set of sensors and programs plus a high-quality ultrasound elastography mode.

About Methodology

The first task when performing ultrasound is to detect the substrate of the disease - venous thrombosis itself. OVT are characterized by individual and often mosaic anatomical localization in the bed of the vena cava. That is why it is necessary to examine in detail and multi-positionally not only the superficial and deep beds of both lower (or upper) extremities, but also the iliocaval segment, including the renal veins. Before performing an ultrasound, it is necessary to familiarize yourself with the available data from the patient’s medical history, which in some cases will help to refine the search and suggest atypical sources of OVT formation. You should always remember the existing likelihood of a bilateral and/or multifocal thrombotic process along the venous bed. The informativeness and value of ultrasound for angiosurgeons is associated not so much with the fact of verification of OVT, but with the interpretation of the results obtained and their decomposition.

Talization. Thus, based on the ultrasound conclusion, presented as “non-occlusive thrombosis of the common femoral vein,” the angiosurgeon, in addition to confirming the fact of OVT, does not receive any other information and, accordingly, cannot determine further tactics in detail. Therefore, in the ultrasound protocol, the identified OVT must necessarily be accompanied by all its characteristics (border, nature, source, extent, flotation length, relation to anatomical landmarks, etc.). At the conclusion of the ultrasound, there should be an interpretation of the results aimed at further determining the tactics by the clinician. The terms “iliocaval” and “iliofemoral” are also clinical, not ultrasound.

About Primary ultrasound

The main technique for verifying OVT during ultrasound is compression of the zone of interest (a fragment of the visualized vessel) by the sensor. It should be noted that the compression force must be sufficient, especially when examining a deep bed, in order to avoid obtaining false-positive information about the presence of thrombotic masses where there are none. A clean vessel that does not have pathological intravenous inclusions, containing only liquid blood, undergoes complete compression when compressed, its lumen “disappears”. If there are thrombotic masses in the lumen (the latter can be of different structure and density), it will not be possible to completely compress the lumen, which can be confirmed by compression of the unchanged contralateral vein at a similar level. The thrombosed vessel has a larger diameter compared to the free contralateral one, and its staining in color mode

commercial Doppler mapping (DCM) will be at least uneven or completely absent.

The study of the iliocaval segment is carried out with a low-frequency convex sensor, however, in some cases, in patients with low body weight, it is possible to use high-frequency linear sensors. In obese patients with severe flatulence, as well as in the presence of adhesive disease after surgical interventions, visualization of the iliocaval segment will be greatly difficult. The use of drugs that suppress and reduce the manifestations of gas formation, as well as cleansing enemas, improves visualization conditions only slightly, and in addition, requires additional time or may be completely contraindicated in patients with suspected OVT of a non-occlusive nature. The use of auxiliary modes, such as color flow, in these cases does not reduce the risk of diagnostic errors. For example, with non-occlusive local thrombosis of the external iliac vein in an obese patient, the lumen of the vessel in the CD mode can be completely stained, and it is not possible to compress the vein. To study the veins of the pelvis and some fragments of the iliac veins in case of poor visualization from a transabdominal approach, it is possible to use intracavitary sensors (transvaginal or transrectal ultrasound). When studying the deep venous bed of the lower extremities in obese patients, as well as in the presence of lymphostasis, when the depth of penetration of the ultrasound beam from a linear high-frequency sensor is insufficient, it is necessary to use a low-frequency convex one. In this case it is possible to determine

border of thrombosis, but the quality of visualization of the actual apex of the thrombus in B-mode will be unimportant. If there is poor visualization of the upper border and the nature of the thrombosis or the venous segment as such, there is no need to give these characteristics in conclusion, remembering the main rule of the ultrasound doctor: do not describe what you did not see or saw poorly. In this case, it is worth making a note that obtaining this information using ultrasound at the time of examination is not possible for technical reasons. It should be understood that ultrasound as a technique has its limitations and the lack of clear visualization of the upper limit and the nature of thrombosis is a reason to use other research methods.

In some cases, visualization of the upper limit and the nature of thrombosis is helped by the Valsalvi test (straining the patient in order to create retrograde blood flow in the vessel under study, in which the diameter of the vein will increase and, possibly, flotation of the thrombus will be visible) and the distal compression test (squeezing the lumen of the vein above the level of thrombosis, at which the diameter of the vessel will also increase, which will improve visual assessment). Figure 1 demonstrates the moment of occurrence of retrograde blood flow in the cerebral vein during the Valsalvi maneuver, as a result of which the floating thrombus, being washed on all sides by the blood flow, took a central position relative to the axis of the vessel. The Valsalvi maneuver, as well as the distal compression test, must be used with caution, since in case of embolic thrombosis, they can provoke PE. In relation to OVT, it is the B-mode that has the greatest diagnostic value. With good visualization, one se-

scale mode for a detailed description of all characteristics of the OHT. The remaining modes (CDC, energy mapping (EC), B-A^, elastography) are auxiliary. In addition, additional modes are to some extent inherent in artifacts that can mislead the doctor. Such artifacts include the phenomenon of “flooding” of the lumen in the CD mode with non-occlusive thrombosis or, conversely, the complete absence of staining of the lumen of a patently patent vessel. There is little chance of diagnosing thrombosis that is not recognized in the B-mode using only auxiliary ones. Also, when drawing up an ultrasound report, you should not completely rely on data obtained only by additional modes.

It was mentioned above that for the competent construction of an ultrasound conclusion, the mere fact of detection of thrombotic masses in the lumen of the vein is not enough. The conclusion should contain information about the nature of thrombosis, its source, the border in relation to ultrasound and anatomical landmarks and - in the case of floating thrombosis - an individual characteristic of its potential embologenicity. A detailed assessment of the listed parameters allows us to determine the indications for conservative treatment or surgical prevention of pulmonary embolism, including the choice of its type.

Occlusive OVT and non-occlusive OVT of a parietal nature, being fixed to the walls of the vessel completely or on one side, respectively, have a low degree of embologenicity and, as a rule, are treated conservatively. A floating thrombus is a thrombus that has a single point of fixation and is surrounded by blood flow from all sides. This

FIGURE 1. Use of the Valsalvi maneuver to improve visualization of the floating thrombus head in B-mode (common femoral vein in the projection of the saphenofemoral junction)

1 - retrograde blood flow in the common femoral vein during straining with the effect of “spontaneous contrast”; 2 - lumen of the common femoral vein; 3 - floating thrombus; 4 - sapheno-femoral anastomosis

FIGURE 2. Floating thrombi with varying degrees of embologenicity (top - thrombus with low risk of PE, bottom - thrombus with high risk of PE)

classic definition of FT. However, in different patients with floating thrombosis, even with the same length of flotation, the degree of embologenicity will be different, and therefore must be determined individually in real time. Thus, in a floating thrombus with a short body length and localization in the superficial femoral vein, the embologenicity will be quite low. A long floating thrombus, which has the appearance of a “worm” and is located in the lumen of the common femoral vein and above, has a greater risk of embolism (Fig. 2). Below we will consider in more detail the characteristics of the floating head of a thrombus from the standpoint of determining its embolic danger.

The need to measure the flotation length, as a rule, is beyond doubt, as is the fact that the larger the value obtained, the worse the prognosis in terms of possible thrombus fragmentation. The thickness of the neck of the thrombus and its ratio to the length of the floating head, as well as the amplitude and type of oscillatory (floating) movements of the head in the lumen of the vein characterize the elastic deformation forces acting on the thrombus, leading to separation. Echo-

The geneity and structure of the thrombus also provide information about the likelihood of fragmentation: the lower the echogenicity and the less homogeneous the structure of the thrombus, the higher the likelihood of its fragmentation. In addition to the characteristics of the tip of the floating thrombus, the upper limit of the thrombus (the zone where the vessel begins to be completely compressed and no longer contains thrombotic masses) and its source are important to determine the degree of potential embologenicity. The higher the threshold of thrombosis, the higher the blood flow speed there. The more venous segments there are anastomoses, the more “washing away” turbulent flows there are. The closer the location of the thrombus head is to the natural bends of the limb (groin, knee), the higher the likelihood of permanent compression of the lumen containing the thrombus. When characterizing the source of thrombosis, it should be remembered that a typical OVT “originates” in small muscle branches giving rise to the medial group of sural veins, and progresses from bottom to top, spreading to the popliteal (PF), then to the superficial femoral (SFE), common femoral vein (CFV). ) and higher. Typical

thrombophlebitis forms in the dilated great saphenous (GSV) and small saphenous (SSV) veins.

Defining and describing a typical OVT using ultrasound does not pose any difficulties. A thrombus with an atypical source in some cases remains undiagnosed, and it is atypical thromboses that are the most embolic. Sources of atypical DVT can be: deep femoral veins (DFE), pelvic veins, injection sites of narcotic drugs (so-called cutaneous vascular fistula), the site of the venous catheter and the catheter itself, renal veins, tumor invasion, gonadal veins, hepatic veins , as well as the transition of thrombosis to the deep veins through the anastomosis and communicants of the affected saphenous veins (Fig. 3). Most often, atypical thromboses are of a floating nature with weak fixation in the neck and are located in the femoral and iliocaval segments. Interventional OVT (post-injection and post-catheter) are formed at the point of damage (alteration) of the vessel, which is also the only point of fixation of the blood clot. Interventional thrombosis is often local

nal, or segmental, i.e., they are determined only in one venous segment (usually the venous segment), while the deep veins above and below the thrombus are passable. Another group of atypical OVTs are combined deep and superficial vein thrombosis. Among them, according to the ultrasound picture, 3 options can be distinguished: 1. Ascending thrombophlebitis in the GSV basin and thrombosis of the medial group (most often) of the sural veins (occurs through the passage of a thrombus from the superficial veins through thrombosed perforating veins).

2 Ascending thrombophlebitis in the basin of the GSV and/or SVC with transition to the deep vein system at the site of the anastomosis of the trunks (saphen-femoral, sapheno-popliteal phlebothrombosis).

3 Various combinations of the above options, up to thrombosis of the OBV with several floating heads. For example, ascending thrombophlebitis in the GSV basin with transition to the SVV at the site of the saphenofemoral junction (SFJ) plus SVV thrombosis with the progression of thrombosis from the deep veins of the leg through the passage of a thrombus from the superficial veins through thrombosed perforators (Fig. 4). The likelihood of developing a combination

The presence of thrombosis of the superficial and deep vein systems and bilateral FT once again confirms the need to perform a complete ultrasound of the venous blood flow of the inferior vena cava system throughout both primary and dynamic studies.

Atypical thrombosis also includes OVT, complicating the course of oncological diseases (thrombosis of the renal veins with a transition to the inferior vena cava is not uncommon). Another atypical source is the deep femoral veins, which are most often affected during operations on the hip joint, as well as the pelvic veins, in which thrombosis occurs in a number of diseases of the organs of this region. The most insidious variant of atypical thrombosis is in situ thrombosis. This is a variant of local segmental thrombosis without an obvious source. As a rule, the site of thrombus formation in these cases is the valvular sinuses with low blood flow velocity in this area. Often, thrombi in situ occur in the iliac veins or venous veins and in most cases are diagnosed after the fact of pulmonary embolism, using second-order imaging methods (computed tomography).

physical phlebography, angiography) or are not diagnosed at all, thereby being a source of “PE without a source”, completely detaching from the vessel wall, leaving no substrate in the lumen of the vein.

The description of mosaic or bilateral OVT should contain detailed information on both lower extremities and on all segments of the lesion separately. The assessment of the potential embolic hazard of a floating thrombus is carried out through a cumulative analysis of its characteristics. To facilitate this process, each of the criteria for a floating thrombus head is assigned 1 or 0 conditional points according to the scheme described below (Table 1). The resulting total score provides a more accurate indication of potential PE. Working according to this scheme allows you to avoid omissions in the assessment of one or a number of criteria and, thus, not only standardize the ultrasound technique, but also improve its effectiveness. When diagnosing a patient with OVT with a high risk of PE, it is necessary to understand that he will probably be indicated for one or another type of surgical prevention of this complication. The main operation for OVT on

FIGURE 3. Various sources of atypical thrombosis (projection of the saphenofemoral junction of the common femoral vein)

1 - source - femoral catheter; 2 - source - cutaneous vascular fistula (drug addicts); 3 - source - great saphenous vein; 4 - source - deep femoral vein; 5 - source - superficial femoral vein

TABLE 1. Determination of the potential degree of embologenicity of floating phlebothrombosis

US criteria Interpretation of US criteria Points

Phlebohemodynamics in the localization zone of the floating head Active 1

Thrombus “outcome” zone Atypical thrombosis 1

Typical thrombosis 0

Ratio of neck width to flotation length (in mm, coefficient) Less than 1.0 1

Greater than or equal to 1.0 0

Flotation with quiet breathing Yes 1

Spring effect during Valsalva maneuver Yes 1

Flotation length More than 30 mm 1

Less than 30 mm 0

Structure of the floating head Heterogeneous, low echogenicity, with contour defects or torn apex 1

Homogeneous, increased echogenicity 0

Dynamics of thrombosis increase Negative 1

Absent or minimal 0

Note. Evaluation of the obtained data. 0-1 point - low degree of potential embologenicity. 2 points - average degree of potential embologenicity. 3-4 points - high degree of potential embologenicity. More than 4 points - an extremely high degree of potential embologenicity.

at the level of the lower extremities itself is the ligation of the PBB. A necessary condition for performing this intervention is to establish the fact of patency of the deep vein vein, as well as the upper limit of thrombosis. Thus, if the floating head moves from the SPV into the SBV, then thrombectomy from the SBV will be necessary. In this case, information about the length of the flotation and the anatomical landmark of the location of the apex of the thrombus (for example, relative to the inguinal fold, SPS, anastomosis of the SPV with the distal GV) will be very important. In case of transition of thrombosis significantly above the level of the inguinal fold, ligation of the external iliac vein (Eiliac vein) is likely to be performed, for which it is also necessary to obtain information about the anatomical landmark of the upper border

thrombosis (for example, its relationship to the anastomosis with the internal iliac vein (SIV) or its distance from the inguinal fold) and the patency of the SVC. All this information should be contained in the descriptive part of the ultrasound protocol.

When an embolic-dangerous VVT is localized in the iliocaval segment, implantation of a vena cava filter or plication of the inferior vena cava (IVC) is most often performed. The vena cava filter or plication zone should be located under the orifices of the renal

FIGURE 5. Upper limit of ascending thrombophlebitis of the great saphenous vein

1 - lumen of the common femoral

2 - thrombus in the lumen of the great saphenous vein; arrow - distance to the safeno-femoral anastomosis

veins to exclude disturbances in venous outflow through the renal veins in case of closure of the IVC lumen distal to this area. In addition, it is necessary to assess the patency of the renal veins themselves, as well as the deep bed of the contralateral side and the veins of the superior vena cava system, since through these veins, if patency, access for intervention will be provided. It is also necessary to indicate the distance from the apex of the thrombus to the renal vein closest to it, since vena cava filters come in different types and differ from one another at least in their size. For the same purposes, it is necessary to indicate the diameter of the IVC during inhalation and exhalation. When the floating head of a thrombus is localized above the mouth of the renal veins, it is necessary to indicate where exactly in relation to the mouths of the renal veins the thrombosis changes its character from occlusive or parietal to actually floating, and measure the length of flotation. If flotation begins below the orifices of the renal veins, it is possible to perform endovascular thrombectomy from the IVC. In case of ascending thrombophlebitis, it is necessary to indicate the upper limit of thrombosis in relation to anatomical landmarks (for example, the distance to the SPS, Fig. 5), as well as the presence and diameter of the upper tributaries of the GSV (in some cases, with pronounced varicose transformation of the upper tributaries, their diameter is greater than the diameter of the trunk GSV, which can lead to ligation of the wrong vessel). It is also important to state the fact that the lumen of the deep vessels (BV, GV, PBB) is intact, excluding the option of combined thrombosis. As a rule, indications for surgical intervention are given when thrombosis moves to the thigh. It should be remembered that with ascending thrombophlebitis, the true limit of thrombosis is practically

technically always above the clinical zone of hyperemia! In case of thrombophlebitis of the GSV with the transition of a thrombus into the lumen of the SVV (combined sapheno-femoral phlebothrombosis), one should remember the need to perform venotomy and thrombectomy from the SVV, which will require information about the length of the floating head of the thrombus in the lumen of the SVV and the anatomical landmark of the localization of its apex in the deep bed . In some cases, in the presence of concomitant thrombosis, it will be necessary to perform simultaneous ligation of the SSV and ligation of the GSV, possibly in combination with thrombectomy. In these cases, information must be given in detail on the deep and superficial beds separately: on thrombophlebitis (thrombosis of the superficial veins with or without transition to the deep bed and in relation to anatomical landmarks) and on phlebothrombosis (deep vein thrombosis, also in relation to anatomical landmarks) according to the algorithms described above.

About Repeated ultrasounds

Ultrasound dynamics of OVT during conservative treatment are interpreted as positive when the flotation length and/or level of thrombosis decreases, as well as when signs of recanalization appear. Another positive aspect is the increased echogenicity and homogeneity of thrombotic masses and the absence of floating movements. Negative dynamics is the registration of reverse processes. Ultrasound dynamics of OVT in the postoperative period are interpreted as positive in the absence of thrombotic masses above the level of deep vein ligation and in the presence of signs of recanalization of thrombotic masses below the ligation site; with preserved blood

flow through the veins above the level of the ligation. Ultrasound dynamics are interpreted as negative in the presence of thrombotic masses above the site of ligation of the deep vein, in case of damage to the deep vein or the appearance of bilateral phlebothrombosis.

Based on dynamic ultrasound data, including the degree of recanalization of thrombotic masses in the postoperative period (as well as during conservative treatment), the effectiveness of anticoagulant therapy is assessed, and drug doses are adjusted. When performing ultrasound after surgery, one should remember the possibility of progression of thrombosis. The greatest risk of this complication occurs in a situation where, in addition to ligation of the SPV, a thrombectomy from the SPV was performed. As thrombosis progresses, “fresh” thrombotic masses are located above the site of vein ligation. The source may be GBV, the site of ligation itself, or the site of thrombectomy. The reason for the progression of thrombosis may be inadequate anticoagulant therapy and/or technical errors in surgical intervention (for example, when ligating a vein above the anastomosis with an GBV - this situation is interpreted not as ligation of the SBV, but as ligation of the SBV).

In case of ascending thrombophlebitis of the GSV, ligation of the GSV at the anastomosis with the GSV or ostial resection of the GSV can be performed. A possible finding in the event of technical errors in performing the operation may be a residual stump of the GSV, often with upper tributaries opening into it or the presence of stump thrombosis. If there is a residual stump, the so-called stump is located. “Mickey Mouse’s second ear”, i.e. during transverse scanning, 3 gaps are determined in the groin projection

TABLE 2. Decrease in mortality from pulmonary embolism

2009 2010 2011 2012 2013 2014 2015

Treated 13,153 1,4229 14,728 15,932 14,949 14,749 10,626

Died 119 132 110 128 143 105 61

Died from pulmonary embolism b 12 11 0 4 3 3

vessel: common femoral artery, GSV and the GSV stump opening into it. The stump of the GSV, especially if the upper tributaries flowing into it are preserved, can serve as a source of progression of thrombosis with transition to the SV. Another finding may be a statement of the actual failure to perform the operation. This is possible in the case of ligation or resection not of the GSV trunk itself, but of one of its large varicose transformed tributaries. This ultrasound picture should be differentiated from a separate upper tributary flowing into the GSV or from a doubling of the GSV trunk. When simultaneously performing ostial resection of the GSV and ligation of the SSV (with or without thrombectomy from the SSV) for combined thrombosis, during postoperative ultrasound, blood flow along the SSV is located, emanating only from the GSV. The presence of additional flows in this case may indicate technical errors in the operation.

The vena cava filter is located in the form of clear hyperechoic signals, different in shape, depending on the type of filter: umbrella or spiral. The presence of clear blood flow in the projection of the vena cava filter, which occupies the entire lumen of the vein during color circulation, indicates its complete patency. In B-mode, the complete patency of the filter is characterized by the absence of thrombotic masses in it, which have the appearance of echo-positive fragments.

There are 3 types of thrombotic lesions of the vena cava filter. 1. Filter embolism due to detachment of the floating head of the thrombus (depending on the size of the occluding head, it can be complete or incomplete, with complete closure of the lumen or with the presence of parietal blood flow).

2. Filter germination due to progression of iliofemoral thrombosis. In this case, it is also necessary to evaluate the safety or absence of blood flow in the inferior vena cava.

3. Filter thrombosis as a new source of thrombus formation (the vena cava filter is a foreign body and can itself serve as an intravenous matrix for thrombus formation).

Extremely rare, isolated observations are cases of migration of the vena cava filter above the established position and progression of thrombosis above the level of the renal veins through the filter (the latter is impeded by blood flow from the renal veins). In the latter case, it is necessary to establish the anatomical landmarks of the upper limit of thrombosis already above the filter level, establish its nature, the presence or absence of flotation and measure its length, i.e., describe all those characteristics that are described during the initial study.

In patients with an implanted vena cava filter or IVC plication, attention should be paid to the presence or absence of a retroperitoneal hematoma, as well as free fluid in the abdominal cavity.

If the patient was implanted with a vena cava filter of a removable design, then a necessary condition for its removal will be a combination of two factors determined by ultrasound: the absence of fragments of thrombotic masses in the filter and the absence of embolic-dangerous thrombi in the inferior vena cava bed. May have me-

one hundred variants of the course of floating PT, when embolism does not occur in the filter: the head does not come off, but continues to remain at its level for several days, maintaining the threat of separation; Moreover, over time, under the influence of anticoagulant therapy, its lysis “in situ” occurs. This is the same case when the vena cava filter is removed without fulfilling its intended purpose.

0 Ultrasound for OVT of the superior vena cava system

In most cases, OVT of the upper extremities are occlusive in nature and are not embolic. The authors did not encounter a floating nature of FT of the superior vena cava bed in any patient. The bed of the superior vena cava is well accessible for ultrasound; difficulties may arise only when visualizing some fragments of the subclavian veins. Here, as in the study of the iliocaval segment, it is possible to use a convex low-frequency sensor, as well as the use of auxiliary modes. The main information that is required from an ultrasound diagnostic physician is to verify the OVT of the superficial or deep bed, or their combined lesion, as well as to describe the occlusive or parietal nature of the thrombosis, since thrombosis of the superficial and deep bed has different conservative treatment. Ultrasound becomes especially important

if there is a suspicion of OVT of the superior vena cava bed in patients with the presence of intravenous catheters (cubital, subclavian). In case of occlusive thrombosis of the venous segment carrying the catheter, its removal is indicated, and in case of atypical non-occlusive catheter thrombosis, when thrombotic masses, localized on the catheter, float in the lumen, it is likely to perform a venotomy with thrombectomy and removal of the catheter. The very fact of diagnosing catheter thrombosis as a probable source of angiosepsis can provide additional information in relation to

bearing on the severity of the patient’s condition and further tactics for its management.

About Conclusion

Ultrasound of venous blood flow is a mandatory study both for the purpose of primary diagnosis of OVT and throughout the entire hospital stage of patient treatment. Wider implementation of ultrasound for preventive purposes, taking into account the risks of venous thrombo-embolic complications in relevant categories of patients, minimizes the onset of both

my pulmonary embolism, and, accordingly, death from it. The methodology for performing ultrasound of venous blood flow presented in the article, combined with the high frequency of the study itself, as well as the active implementation of endovascular methods of surgical prevention of PE (used in the Central Clinical Hospital of the Russian Academy of Sciences since 2012), led to a significant decrease in mortality from PE, which is reflected in Table 2 (2015 - data at the time the article was submitted to the editor as of the beginning of October).

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Ultrasound diagnosis of acute venous thrombosis

Acute venous thrombosis of the inferior vena cava system is divided into embologenic (floating or non-occlusive) and occlusive. Non-occlusive thrombosis is the source of pulmonary embolism. The superior vena cava system accounts for only 0.4% of pulmonary embolism, the right side of the heart - 10.4%, while the inferior vena cava is the main source of this formidable complication (84.5%).

A lifetime diagnosis of acute venous thrombosis can be established only in 19.2% of patients who died from pulmonary embolism. Data from other authors indicate that the frequency of correct diagnosis of venous thrombosis before the development of fatal pulmonary embolism is low and ranges from 12.2 to 25%.

Postoperative venous thrombosis is a very serious problem. According to the B.C. Savelyev, postoperative venous thrombosis develops after general surgical interventions on average in 29% of patients, in 19% of cases after gynecological interventions and in 38% after transvesical adenomectomies. In traumatology and orthopedics this percentage is even higher and reaches 53-59%. A special role is given to early postoperative diagnosis of acute venous thrombosis. Therefore, all patients at risk for postoperative venous thrombosis should undergo a complete examination of the inferior vena cava system at least twice: before and after surgery.

It is considered fundamentally important to identify violations of the patency of the main veins in patients with arterial insufficiency of the lower extremities. This is especially necessary for a patient in whom surgical intervention is proposed to restore arterial circulation in the limb; the effectiveness of such surgical intervention is reduced in the presence of various forms of obstruction of the main veins. Therefore, all patients with limb ischemia should have both arterial and venous vessels examined.

Despite the significant advances achieved in recent years in the diagnosis and treatment of acute venous thrombosis of the inferior vena cava and peripheral veins of the lower extremities, interest in this problem has not only not diminished in recent years, but is constantly increasing. A special role is still assigned to the early diagnosis of acute venous thrombosis.

Acute venous thrombosis, according to its localization, is divided into thrombosis of the ilicaval segment, femoral-popliteal segment and thrombosis of the veins of the leg. In addition, the great and small saphenous veins may be susceptible to thrombotic damage.

The proximal border of acute venous thrombosis can be in the infrarenal portion of the inferior vena cava, suprarenal, reaching the right atrium and located in its cavity (echocardiography is shown). Therefore, examination of the inferior vena cava is recommended to begin with the area of ​​the right atrium and then gradually go down to its infrarenal section and the place where the iliac veins flow into the inferior vena cava. It should be noted that the closest attention must be paid not only to examining the trunk of the inferior vena cava, but also the veins flowing into it. First of all, these include the renal veins. Typically, thrombotic lesions of the renal veins are caused by a mass formation in the kidney. It should not be forgotten that the cause of thrombosis of the inferior vena cava can be the ovarian veins or testicular veins. Theoretically, it is believed that these veins, due to their small diameter, cannot lead to pulmonary embolism, especially since the distribution of the thrombus to the left renal vein and the inferior vena cava along the left ovarian or testicular vein due to the tortuosity of the latter looks casuistic. However, it is always necessary to strive to examine these veins, at least their mouths. In the presence of thrombotic occlusion, these veins increase slightly in size, the lumen becomes heterogeneous, and they are well located in their anatomical areas.

With ultrasonic triplex scanning, venous thrombosis is divided in relation to the lumen of the vessel into parietal, occlusive and floating thrombi.

Ultrasound signs of parietal thrombosis include visualization of a thrombus with the presence of free blood flow in this area of ​​the altered lumen of the vein, the absence of complete collapse of the walls when the vein is compressed by a sensor, the presence of a filling defect during color circulation, and the presence of spontaneous blood flow during spectral Dopplerography.

Thrombosis is considered occlusive, the signs of which are the absence of collapse of the walls when the vein is compressed by a sensor, as well as the visualization of inclusions of varying echogenicity in the lumen of the vein, the absence of blood flow and staining of the vein in spectral Dopplerography and Color Doppler modes. Ultrasound criteria for floating thrombi are: visualization of the thrombus as an echogenic structure located in the lumen of the vein with the presence of free space, oscillatory movements of the apex of the thrombus, absence of contact of the vein walls during compression with the sensor, presence of free space when performing respiratory tests, envelope type of blood flow with color coding of the flow , the presence of spontaneous blood flow during spectral Doppler sonography.

The capabilities of ultrasound technologies in diagnosing the age of thrombotic masses are of constant interest. Identification of signs of floating thrombi in all stages of thrombosis organization allows increasing the efficiency of diagnosis. Particularly valuable is the earliest diagnosis of fresh thrombosis, which allows early measures to be taken to prevent pulmonary embolism.

After comparing the ultrasound data of floating thrombi with the results of morphological studies, we came to the following conclusions.

Ultrasound signs of a red thrombus are a hypoechoic indistinct outline, anechoic thrombus in the apex and hypoechoic distal part with individual echogenic inclusions. Signs of a mixed thrombus are a heterogeneous structure of the thrombus with a hyperechoic clear outline. The structure of the thrombus in the distal sections is dominated by heteroechoic inclusions, in the proximal sections - predominantly hypoechoic inclusions. Signs of a white thrombus are a floating thrombus with clear contours, a mixed structure with a predominance of hyperechoic inclusions, and with CDK, fragmentary flows through thrombotic masses are recorded.