engleski

New Insight In Neurosonology

During the last two decades, ultrasound examination has offered clinicians both spectral Doppler analysis and real-time ultrasound imaging. This union, known as Dopper ultrasound, has reached far more applications beyond the early carotid artery evaluations. Superposition of color coded flow imaging enabled more information, providing insight into complete evaluation of the morphology of the vessels of the head and neck, as well as their hemodynamic. Although thought of as inaccessible, the insight of adult brain parenchyma is possible with the superposition of color-coded flow imaging of the Willis circle and vertebrobasilar system. Thus transcranial Doppler evaluation provides supporting documentation for proper diagnosis and functional testing, and in combination with the easy transportable equipment, enables quick, easy and reliably bedside evaluation of stroke patients. The easy and noninvasive diagnostics is nowadays the must in diagnosis, management and monitoring of stroke patients. Neurosonology includes both extracranial and intracranial noninvasive cerebrovascular evaluation. Informations of carotid intima-media thickness by means of high-resolution ultrasound are available, since its thickening represent subclinical atherosclerosis. Epidemiological studies obtained from different investigations have shown variability in CCA IMT (in 65-year-old males about 0.80.73 mm). The results mostly show that males have greater IMT compared to females, and the rate of progression is 0.01 mm per year. It seems that all known atherosclerosis risk factors influences IMT like hypertension, especially the increase of systolic blood pressure, higher cholesterol and LDL cholesterol, cigarette smoking, diabetes mellitus, some hematological parameters like fibrinogen levels, fibrinopeptid A, D-dimer, tissue plasminogen activator and plasminogen activator inhibitor, serum copper, and homocystein level. No correlation was found with the triglyceride levels and HbA1 C levels in patients with diabetes mellitus, nor alcohol consumption. In patients with coronary heart disease, increased IMT was found. Individuals with increased IMT had greater risk for myocardial infarction, stroke and ischemic stroke. It adds reliable informations for pharmacological interventions on risk factors like statin or antihypertensive therapy, thus lowering the stroke risk. Duplex ultrasound imaging combines high-resolution gray scale imaging and pulsed Doppler spectral analysis to yield excellent anatomic and physiologic data. The standard diagnostic tool used to examine the extracranial cerebrovascular system is color-coded duplex ultrasound imaging. The superposition of color-flow imaging aids the examiner and interpreter the information of the vessel orientation, anatomic variants, hemodynamic evaluation and various physiologic variants, as well as pathologies. The color and power Doppler imaging provides additional information on extracranial brain hemodynamic, making the evaluation more precise and reliable. Parallel with the vessel wall analysis, the search for plaques is performed. In plaque analysis the morphology, length and echogenicity are evaluated, the plaques surface characteristics and the degree of the vessel stenosis. Plaque morphology is important, since different echogenicity express different stroke risk. They may be homogenous or heterogeneous. Homogeneous plaques have a uniform appearance with or without acoustic shadowing. The heterogeneous plaques have a mixture of low, mid and high-level echoes. Low level echoes are the results of lipid, cholesterol, cell debris, necrotic material or intraplaque hemorrhage due to the rupture of small, vulnerable vessels. The differentiation between these substances is impossible, but nevertheless, all of these substances represent instability of the plaque, with the high risk of embolization or growth. Higher level of echoes usually represents fibrinous material, and high levels of echoes are the result of calcifications. Calcifications can be recognized by total reflection of the ultrasound beam, performing acoustic shadow, which makes the analysis of the tissue layers under the plaque impossible. These plaques are less harmful, and have a lower potential of embolization or smaller growing potential. In The Second International Consensus Meeting, criteria were determined for the characterization of carotid plaques. Plaque compositions are thus characterized in five steps, according to the echogenicity and risk of stroke. The anechoic plaques had highest risk for stroke, and with the increase of echogenicity, the risk of stroke was lower. The degree of internal carotid artery stenosis may be determined by means of color-coded Doppler ultrasound. In the evaluation of the degree of stenosis more parameters were analyzed, with peak systolic velocity in the internal carotid artery as the most sensitive criteria for determination of the advanced carotid stenosis. Color coded Doppler sonography proved to be highly sensitive method in evaluation of the degree of stenosis, in most instances replacing angiography, with the advantages of plaque morphology information. Besides atherosclerotic changes, vasculitis, nonatherosclerotic vasculopathies and dissections can be found. Vasculitis of the nervous system includes a group of disorders characterized by the histological feature of blood vessels inflammation. The diagnose is suspected by the clinical presentation, and confirmed by signs of inflammation obtained with laboratory analysis, or biopsy. Doppler sonography may help in noninvasive visualization of the disease, if the location of the disease is present in a segment that is accessible to the ultrasound investigation. The localization of the giant cell arthritis is mostly extracranial ; the granulomatous inflammation affects branches of the aortic arch. In neurological setting, a prominent manifestation is cranial arteritis, most often as temporal arteritis, displaying a dark halo in acute phase, and the increase of echogenicity as a sign of fibrous healing. Dissections may appear as different findings in color-coded Doppler mode. When extending from aortic arch, double lumens can be seen. Bifurcation stenosis may dissect leading to the formation of color-coded flow in the plaque base. In younger persons dissections are usually affecting distal parts of the internal carotid arteries or vertebral arteries. Hypoechoich stenosis of the vessels in distal parts can be seen, or when located intracranial, and leading to complete occlusion, the indirect signs of distal occlusions are present. Such signs include dampened flow, with high resistance pattern, and possible inversed hemodynamic during diastole. Beside carotid arteries, the physiologic variants and pathologic conditions like atherosclerotic, inflammatory changes and dissections in the vertebral arteries can be visualized. Although one fourth of ishemic strokes are related to the vertebrobasilar territory, the investigations of the vertebral arteries haven't become so popular. The reason is the technical problem due to anatomic position of the vessels, a very low rate of vertebral endarterectomies, and a low rate of vertebral stenosis as a cause of vertebrobasilar strokes. Vertebral occlusions may clinical present as a TIA, or a mild stroke. Most often, in population, a high proportion of the variations of vertebral arteries are found, as asymmetry, hypoplasia, or extravertebral flow. Stenosis or occlusions are more often in V1 (prevertebral) part, although may also happen in intravertebral or intracranial parts. Thus the changes in hemodynamic spectra's may point up on the more proximal of distal disease. Subclavian steal syndrome as a consequence of proximal steno occlusive disease of the subclavian artery leads to the changes in the hemodynamic spectra's in vertebral arteries. The noninvasiveness and time resolution of the measurement enables follow up of atherosclerotic, inflammatory vessel wall diseases and of dissections. Three- and four-dimensional ultrasound enables more informations on plaque stability, and more precise diagnose on the degree of stenosis. Application of M-mode, as well as 3-D ultrasound enables measurement of distensibility as additional criteria of subclinical atherosclerosis measurement. Transcranial Doppler (TCD) proved to be a noninvasive, fast and exact diagnostic tool for the evaluation of cerebral hemodynamic, providing numerous informations on cerebrovascular state of the patient. The greatest advantage of TCD is the possibility of time resolution of the measurement, and due to its noninvasiveness, it can be repeated as frequently as needed or applied for continuous monitoring. It is frequently less expensive than other techniques and dye contrast agents are not used. The application does not require large sophisticated equipment, thus enabling easy transport of the TCD, and bedside evaluation of patients. It allows noninvasive evaluation of the intracranial hemodynamic in stroke patients, localization of intracranial artery stenosis or occlusion, assessment of collateral flow in extra- or intracranial arterial stenosis or occlusion, monitoring of the recanalization and enhancement of the rt-TPA induced recanalization, assessment of vasospasm in hemorrhagic stroke and trauma, and screening for vascular malformations. In intensive care unites, evaluation of the intracranial pressure can be monitored, as well, as the development of the cerebral circulatory arrest, defining the exact time of the brain death. Monitoring of the cerebral circulation is possible during surgery. Recent TCD modalities enable detection of cerebral microemboli for cardiac source, aortic arch or large cerebral arteries, estimation of cerebral vasoreactivity, and cerebral autoregulation by analyzing cerebral microcirculatory responses after different stimulation tests. The application of contrast agents can provide useful information in right-to-left cardiac or extracardiac shunts, since the results are comparable with contrast transesophageal echography (TEE). TEE provides direct anatomic information regarding the site and nature of the right-to-left shunts due to patent foramen ovale (PFO) or presence of an atrial septal aneurism, but TCD can assess the extent of the communication, and can be useful in control of the PFO closure. The development of the probes and equipment enables the combination of brain parenchyma visualization and hemodynamic analysis by means of Transcranial Color Coded Duplex Sonography (TCCS). TCCS adds two-dimensional gray-scale real-time and color Doppler imaging to conventional TCD. Evaluation of intracranial brain parenchyma and hemodynamic enables differentiation between ischemic and hemorrhagic stroke, assessment of the localization of arterial occlusion, monitoring of the cerebral thrombolysis, monitoring of midline shift in space-occupying stroke, assessment of collateral flow in extra- or intracranial arterial stenosis or occlusion. In hemorrhagic stroke visualization of larger cerebral aneurisms or larger or medium sized arteriovenous malformations are possible as well as the assessment of their feeding vessels. It is possible to assess and monitor cerebral vasospasm in brain hemorrhage. The use of sonographic contrast agents can increase the number of conclusive TCCS studies in patients with insufficient acoustic windows, enables cerebral perfusion assessment, measurement of arteriovenous cerebral transit time, which might enable the detection of small-vessel disease. New research on sitetargeted ultrasound contrast agents may improve diagnosis and local drug delivery. These techniques allow noninvasive evaluation of the extra- and intracranial hemodynamic in symptomatic or asymptomatic patients with known risk factors to assess the impairment of hemodynamic due to extracranial or intracranial large artery arteriosclerosis or advanced cardiac disease. It proved to be an excellent diagnostic tool in stroke prevention in certain hematological disease especially in sickle-cell anemia. Beside neurovascular disorders it enables insight into cerebral hemodynamic in other neurological patients like migraine, epilepsy and cognitive disorders. It was proved for estimation of the substantia nigra degeneration in Parkinson's disease and may show alterations in psychiatric diseases. Neurosonology cover techniques that enable noninvasive and objective diagnostic tool for the assessment of cerebral hemodynamic in patients with cerebrovascular diseases, risk factors for stroke or other neurological diseases. It is irreplaceable method for stroke classification and monitoring in intensive care units. Cerebrovascular ultrasonography has experienced an almost exponential growth over the last few decades. Many ultrasound techniques are available for routine noninvasive examination of the extracranial arteries for detection and quantification of stenosis, evaluation of plaque stability, diagnosis and follow up of dissections, evaluation of intracranial hemodynamic and the redistribution in collateral flow presence. New software enables noninvasive emboli detection, and functional imaging. All this enables the complete diagnosis of the patients with the risk for stroke, as well as the application in stroke patients. The great advantage is that the methods are easy, reliable, noninvasive, and can be repeated as much as needed.

extracranial doppler sonography; transcranial doppler sonography; IMT

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