Duplex scanning of head and neck vessels

Where to do an ultrasound of the head and why is echoencephalography necessary, let's consider these questions. Ultrasound of the head is a diagnostic method that can be used to identify pathologies of the brain. The study is based on harmless ultrasound radiation that penetrates through the tissues and bones of the skull into the substance of the brain.

Duplex scanning (gray-scale echography with color Doppler coding and spectral Doppler analysis, as applied to the intracranial part of the cerebral vascular system - transcranial duplex scanning) currently serves as the main method for diagnosing various types of pathology of the cerebral vascular system. Duplex scanning combines the ability to visualize the lumen of the vessel and tissues surrounding the vessel in B-mode (two-dimensional gray-scale echography mode) and simultaneous analysis of the hemodynamic state using Doppler technologies. Based on the results of the B-mode examination, it is possible to obtain data on the state of rigidity and elasticity of the vascular wall (elastic-elastic characteristics), the functional state of the endothelium (its vasomotor activity), the presence, nature and prevalence of changes in the structure and thickness of the vascular wall, disruption of the integrity of the vascular wall (dissection), the presence of intraluminal formations, their localization, length, echogenicity (indirect density characteristic), the degree of disruption of the patency of the vessel lumen, changes in the diameter of the vessel, vascular geometry (the presence of deformations, deviations of the course of the vessel from the usual anatomical trajectory), anomalies of the origin, course and branching of vessels. Information on intraluminal flows (as a result of processing the reflected Doppler signal using the fast Fourier transform method) during conventional and transcranial duplex scanning can be presented in the form of color cartograms (color Doppler mode) and/or Doppler spectra (spectral Doppler mode). Based on the study data in the color Doppler mode, qualitative information on the blood flow is obtained [presence, nature (laminar, turbulent), defects in filling cartograms, etc.]. The spectral Doppler mode allows for a quantitative characterization of intraluminal flows, i.e. to objectify the presence or absence of hemodynamic disturbances, as well as to determine the degree of their severity. The diagnostic information obtained in this case is based on the analysis of velocity indicators and various calculated indices indirectly characterizing the level of peripheral resistance and the tone of the vascular wall.

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Indications for examination of extracranial sections of vessels

• clinical signs of acute or chronic cerebrovascular insufficiency, including headache syndrome;
• risk factors for the development of cerebrovascular diseases (smoking, hyperlipidemia, obesity, arterial hypertension, diabetes mellitus);
• signs of damage to other arterial basins in the case of systemic vascular processes;
• planning surgical interventions for various types of cardiac pathology, primarily ischemic heart disease (coronary artery bypass grafting, coronary artery stenting);
• pathology of surrounding organs and tissues with potential extravasal effects;
• clinical signs of jugular vein pathology (usually thrombosis).

High resolution of ultrasound duplex scanning combined with non-invasiveness and the possibility of multiple repeated studies makes the method an indispensable tool not only in clinical neurology, but also in the implementation of full-fledged preventive screening in the asymptomatic population. Unlike ultrasound Dopplerography, it can detect small and medium stenosis of the carotid arteries, significantly expanding the possibilities of differential diagnostics. In this regard, it can be stated that duplex scanning is the main screening method in individuals without clinical symptoms of cerebrovascular disorders.

Indications for transcranial duplex scanning

• detection of stenotic/occlusive pathology in the extracranial sections of the brachiocephalic arteries using duplex scanning (or ultrasound Dopplerography) - a potential source of cerebral blood flow disorders;
• the presence of indirect signs of damage to intracranial arteries;
• signs of acute or chronic cerebral ischemia without established specific causes of its development;
• headache syndrome;
• systemic vascular disease is a potential source of development of cerebrovascular disorders (arterial hypertension, diabetes mellitus, systemic vasculitis, etc.).
• pathology of the brain substance (detected using other imaging techniques - CT, MRI, scintigraphy, etc.), accompanied by changes in its structure and cerebral vascular circulation, clinical signs of intracranial hypertension;
• the need for dynamic monitoring of cerebral blood flow parameters to assess the effectiveness of therapy in the acute period of ischemic and hemorrhagic stroke and in chronic cerebrovascular insufficiency, as well as to determine the state of blood vessels at various stages of surgical revascularization, regardless of the type of the latter.

The objectives of ultrasound examination of the arterial and venous systems of the brain at the extra- and intracranial level:

• diagnostics of stenotic/occlusive pathology in the arterial and venous systems of the brain, assessment of its pathogenetic and hemodynamic significance;
• identification of a complex of disorders associated with systemic vascular diseases;
• detection of vascular developmental anomalies, arterial and venous aneurysms, arteriovenous malformations, fistulas, cerebral vasospasm, venous circulation disorders;
• identification of early (preclinical) signs of systemic vascular pathology;
• monitoring the effectiveness of treatment;
• determination of the functions of local and central mechanisms of regulation of vascular tone;
• assessment of the reserve capacity of the cerebral circulatory system;
• establishing the possible etiological role of the identified pathological process or symptom complex in the genesis of the clinical syndrome (syndromes) present in a specific patient.

The mandatory scope of the study when conducting duplex scanning of the extracranial sections of the brachiocephalic arteries includes the distal section of the brachiocephalic trunk, the common carotid arteries along their entire length, the internal carotid arteries before entering the cranial cavity through the canalis caroticus, the external carotid arteries in the proximal sections, and the vertebral arteries in segments V1 and V2. If indirect signs of damage to segment V3 are detected, echolocation can also be performed in this section of the vertebral artery.

When signs of pathology are detected that potentially threaten the development of systemic (intracranial) hemodynamic disorders, Doppler characteristics of blood flow in the supratrochlear (ophthalmic) artery are necessarily examined.

In the carotid arteries at the extracranial level, various stages of pathological processes can be identified with a full structural analysis of intraluminal pathology. Due to the anatomical features of their location, the vertebral arteries are visualized fragmentarily and are accessible only to monoplane scanning. This limits the capabilities of the method in diagnosing various pathological processes. In particular, with high reliability in conditions of low-quality visualization, it is possible to identify only stenotic lesions with a narrowing of the vessel lumen by more than 40-50% in diameter, located in areas accessible to location. Echostructural analysis of intraluminal formations in the vertebral artery is usually not performed due to the extremely limited capabilities of visualizing the vessel walls. Load testing is performed to determine functional changes in the diameters of the vessels. There are no specific objective ultrasound signs of extravasal compression of the vertebral artery in the canal of the transverse processes of the cervical vertebrae and in the area of the craniovertebral joint. Doppler diagnostic criteria used for these purposes in everyday practice are indirect in nature and require mandatory confirmation by methods that allow visualization of the area of extravasal impact (angiographic techniques in the background or with functional stress tests).

The study of the jugular veins (internal and external), as well as the veins of the vertebral venous plexus, is performed if thrombosis of these vessels is suspected. The diagnostic value of Doppler blood flow indices obtained in the spectral Doppler mode from the lumens of the above-mentioned venous collectors, and their significance in determining pathological changes in cerebral venous hemodynamics in all other cases is questionable, given the variability of venous outflow from the cranial cavity with changes in body position, as well as the inconsistency of the structure of the veins themselves, the synchronization of blood flow in them with breathing and the slight compressibility of the lumens.

The study of the vascular system of the brain by transcranial duplex scanning has a number of features. Given the presence of an obstacle in the path of ultrasound beams in the form of cranial bones, a low radiation frequency (on average 2-2.5 MHz) is used to increase penetrating ability. At such frequencies, visualization of the vascular wall and determination of the state of the lumens of intracranial arteries and veins is fundamentally impossible. The information obtained is indirect and is based on the results of the analysis of color cartograms of the flows of intracranial arteries and veins, as well as the corresponding Doppler spectra. Therefore, with transcranial duplex scanning, as well as with transcranial Dopplerography, the assessment of vascular changes and diagnosis of processes not accompanied by the formation of local (and systemic) hemodynamic disorders is impossible. Due to the different thickness of the skull bones, which determines their different permeability to ultrasound radiation, echolocation is performed in certain zones called ultrasound "windows", which are no different from those in transcranial Dopplerography. The volume and quality of information obtained during transcranial duplex scanning depend on the presence and severity of ultrasound "windows". The main limitations in this case are due to a significant decrease in the quality of ultrasound imaging with a decrease in the acoustic "transparency" of the skull bones.

When performing transcranial duplex scanning, the mandatory research protocol includes the study of color flow maps, the Doppler spectrum and its characteristics in the middle cerebral arteries (segments M1 and M2), the anterior cerebral arteries (segment A1), the posterior cerebral arteries (segments P1 and P2), the siphon of the internal carotid artery and its intracerebral portion, the vertebral arteries in segment V4, the basilar artery and a number of venous trunks (veins of Rosenthal, vein of Galen, straight sinus). To determine the functional capacity of the connecting arteries of the circle of Willis (in cases of hemodynamic balance), compression tests are performed (short-term, for 3-5 s, compression of the lumen of the common carotid artery above the orifice). Such manipulation leads to characteristic changes in blood flow in the A1 segment of the anterior cerebral artery (with the functional competence of the anterior communicating artery) and the P1 segment of the posterior cerebral artery (with the functional competence of the posterior communicating artery). The functional competence of other macroanastomoses (pericallosal, extracranial) in the absence of signs of blood flow collateralization at rest is not determined. Currently, issues related to the use of visualizing ultrasound methods in the clinic of urgent angioneurology are being actively developed. Based on the capabilities of duplex scanning, the objectives of the study in acute cerebrovascular accidents of the ischemic type are as follows.

• Determination of possible causes of ischemic stroke.
• Study and assessment of background blood flow parameters in extra- and intracranial arteries and veins and the state of reactivity of the cerebral circulatory bed.
• Establishing sources of collateral redistribution of flows, their viability and sufficiency.
• Monitoring the level of blood flow in one or more vessels to confirm the effectiveness of pathogenetic and symptomatic therapy.

Duplex scanning allows us to presumptively determine possible causes of ischemic stroke.

When examining the extracranial sections of the brachiocephalic arteries, it is possible to identify differential signs characteristic of stenosing atherosclerosis, thrombosis, macroembolism, angiopathies, and vasculitis. Transcranial duplex scanning makes it possible to verify stenosing/occlusive lesions by determining the degree of their severity without specifying morphological equivalents, as well as to identify specific phenomena characteristic of a breakdown in autoregulation of cerebral blood flow, cerebral angiospasm, etc. When detecting stenosing atherosclerotic lesions of the carotid arteries, an analysis is made of the echostructure of the atherosclerotic plaque and the degree of obstruction of the lumen of each affected vessel. According to the existing classification of atherosclerotic plaques by echostructure and echogenicity, a distinction is made between homogeneous (low, moderate, increased echogenicity) and heterogeneous (with a predominance of hypoechoic and hyperechoic components, with the presence of an acoustic shadow). Complicated plaques include atherosclerotic plaques with ulceration, hemorrhage and atherothrombosis. The latter lesions are classified as so-called unstable; they are the most dangerous in terms of the development of cerebral embolism and thrombosis. If the embolic nature of ischemic stroke is suspected, it is first of all necessary to pay attention to the atherosclerotic plaques of the above types. The degree of vessel narrowing may not play a significant role, since complicated plaques are often those accompanied only by local changes in hemodynamics due to an insignificant (up to 40-50%) reduction in the arterial lumen. In the absence of obvious causes of arterio-arterial embolism, and in some cases even if they are present, an echocardiographic examination is necessary to exclude the cardioarterial genesis of cerebrovascular accident.

The second possible cause of acute ischemia is occlusion (or non-occlusive thrombosis) of cerebral arteries at the extra- and/or intracranial level. In thrombosis of the extracranial sections of the carotid and/or vertebral arteries, a typical ultrasound picture is determined, including intraluminal formations of varying echogenicity and length, leading to restructuring of local and systemic hemodynamics, determined in the spectral Doppler mode. In some cases, when analyzing the echogenicity, geometry, degree of mobility, and prevalence of the intraluminal formation, it is possible to differentiate a primary (associated with damage to the vascular wall) mural thrombus from an embolus. Additional arguments in favor of the latter are detection of an atypically located obstruction (e.g. bifurcation of the common carotid artery with free lumens of the internal and external carotid arteries), unchanged or slightly changed vascular wall in the area of the formation, and concomitant arterial spasm. When stenosis and occlusion are localized in intracranial arteries, pronounced changes in blood flow are determined in the form of narrowing (disappearance) of the color flow map in the area of stenosis (occlusion) of the artery, a decrease in the speed indicators of blood flow in combination with changes in the spectral characteristics of blood flow proximally and (possibly) in the area of the lesion. In parallel with this, as a rule, it is possible to register signs of collateralization of blood flow through the system of natural anastomoses (provided that they are available and competent).

The echographic picture looks different in case of non-occlusive thromboses of intracranial arteries. The main difference in this case will be the absence of a local hemodynamic difference in the area of the obstacle, probably due to the complex configuration of the stenotic canal. This circumstance often becomes a source of diagnostic errors in transcranial duplex scanning and discrepancies with the data obtained during angiography.

In the acute period of ischemic stroke, it is essential to study the cerebral blood flow indices at rest both in the vessels supplying the areas of developing focal lesions of the brain tissue and in other basins accessible for examination. The development of ischemic stroke may be a consequence of a breakdown of the autoregulatory mechanisms of cerebral blood flow, in other cases it is accompanied by such a breakdown. In this regard, pathological changes in cerebral blood flow in one or more vascular basins can be registered in most patients. When autoregulation is disrupted at its lower limit (with a critical drop in intraluminal pressure), a marked decrease in blood flow velocity indices is observed, and hyperperfusion develops at the upper limit, accompanied by an increase in the velocities of intraluminal flows. The causes of cerebral hypoperfusion are most often stenotic/occlusive lesions or situations with an acute drop in systemic arterial pressure. Cerebral hyperperfusion is usually based on a pathological increase in systemic arterial pressure. At the same time, in case of local failure of autoregulation in individuals with hypertension (usually in areas of adjacent blood supply) with the formation of lacunar infarctions, background blood flow indices in the main afferent arteries may not differ significantly from the average normative ones. At the same time, load testing aimed at activating autoregulation mechanisms allows registering local and/or generalized disorders of cerebrovascular reactivity. It is equally important to study the presence, consistency and degree of functional activity of the system of natural anastomoses. Objectification of adequate compensatory redistribution of blood flow through them in case of stenotic/occlusive lesions of the brachiocephalic vessels is a favorable prognostic sign. In cases where collateralization of blood flow is not observed at rest, compression tests should be used to determine its potential sources. The latter requires caution in case of widespread atherosclerotic lesions of the carotid arteries.

In case of atherothrombotic and cardioembolic ischemic stroke, pathogenetic treatment can be carried out - thrombolytic therapy. Duplex scanning allows monitoring blood flow and determining vascular reactions in the affected area both in systemic and selective thrombolysis. Normalization of flow in the affected vessel or an increase in the blood flow velocity in its lumen, a decrease in the intensity or disappearance of collateralization are objective signs of the effectiveness of therapy. The absence of positive dynamics of the echographic picture can be regarded as a criterion for its ineffectiveness. Often, there may be discrepancies between the success of revascularization and the clinical effect.

The main objective of ultrasound imaging methods (as well as USDG and TCDG) in hemorrhagic stroke is to monitor arterial and venous blood flow in intracranial arteries and veins to determine the presence and severity of cerebral vasospasm and intracranial hypertension. Ultrasound diagnostics of cerebral angiospasm is based on recording pathological increases in linear blood flow velocity indices in spasmodic arteries (peak systolic velocity, time-averaged maximum blood flow velocity) and the results of determining the Lindegard index (the ratio of peak systolic velocity in the middle cerebral artery to the same index in the internal carotid artery). A change in the response to metabolic functional load tests can be used as an additional sign of angiospasm. By monitoring Doppler parameters of cerebral blood flow, timely and adequate drug correction of vasospastic reactions is possible.

Various types of cerebrovascular accidents, as well as other pathological conditions, can cause critical cerebral perfusion disorders with subsequent development of brain death. Duplex scanning is one of the basic methods that provides valuable information in this condition. The basis for the conclusion about the presence of signs of cessation of cerebral circulation is the results of the assessment of linear and volumetric indicators of blood flow in the extracranial sections of the brachiocephalic arteries, as well as linear indicators of blood flow in the intracranial vessels. In the extracranial sections of the internal carotid arteries and vertebral arteries, signs of blood flow reverberation can be detected. The value of hemispheric cerebral blood flow is below the critical values of 15-20 ml/100 g/min. With transcranial duplex scanning, signs of arterial blood flow in the intracranial arteries are absent.

In chronic cerebral circulation disorders of various genesis (atherosclerotic, caused by hypertensive, diabetic angiopathies, age-related involution, vasculitis, severe heart diseases accompanied by circulatory failure, etc.), duplex scanning of the extracranial sections of the brachiocephalic arteries can reveal signs of various pathological processes that are not always directly related to the development of cerebral blood flow disorders. Unlike acute cerebral catastrophe, in chronic cerebral circulation disorders against the background of atherosclerotic lesions of the aortic arch branches, the degree of stenosis of the brachiocephalic arteries and the prevalence of the process are more important, given the role of these factors in the genesis of chronic cerebral ischemia and the limitation of the possibilities of adequate collateral compensation.

Duplex scanning, like any other ultrasound technique, is operator-dependent and to a certain extent subjective. The success of using a set of visualizing ultrasound methods in clinical neurology, in addition to the operator's experience and skills, largely depends on the technical characteristics of the equipment used. In this regard, in all controversial diagnostic cases, as well as when planning surgical treatment of the brain vessels, the reference method in relation to ultrasound is X-ray contrast angiography and its varieties, recognized as the "gold standard" in angiology.

Ultrasound is an excellent alternative to expensive MRI or CT examination. Diagnostics does not require special preparation and is approved for patients of all ages, both pregnant women and newborns. The procedure lasts 20-25 minutes, it is painless and safe for the body.