**2. Ultrasound examination of cerebroafferent vessels: Extracranial carotid axis**

Ultrasound examination of the extracranial carotid artery (common and internal carotid artery) is a useful and standardized technique and it represents, in patients with a focal neurological symptom, the ideal screening tool for the identification of carotid stenosis and occlusion and the selection of lesions amenable to surgical or endovascular treatment. Atherosclerosis is a relevant cause of transient ischemic attack and stroke, but also non atherosclerotic conditions, like spontaneous cervical artery dissection and arteritis, can be diagnosed and followed-up. In acute stroke patients the involvement of the extracranial carotid axis is the cause of the cerebrovascular event quite in 18%, being the majority of vessel lesions in the intracranial circulation and sometimes both in extracranial and intracranial circulation (Malferrari G et al. 2007). For both atherosclerotic and nonatherosclerotic diseases, the ultrasound findings and the diagnostic criteria has been compared to the neuroradiological findings and criteria in the literature, whereas Digital Subtraction Angiography (DSA) is considered the gold standard.

#### **2.1 Atherosclerotic carotid stenoocclusion**

Atherosclerotic involvement of the extracranial carotid artery is not the main cause of vascular lesions in acute stroke patients. It has been reported in about 18% of patients in a 6 hours time window, whereas the intracranial large vessel stenoocclusion accounts for 52.8%. There are two main mechanisms by which the carotid atherosclerotic disease may lead to cerebral infarction: first, an embolic mechanism, as an artery to artery embolism from the plaque rupture; second, an hemodynamic mechanism, because of the blood flow reduction downstream the stenoocclusion. The first one is linearly related to the severity of the carotid stenosis, increasing as the stenosis increases, but the second one is not related to the severity of the stenosis and it depends on multiple factors, as the cerebrovascular reserve, the collateral circulation failure, the time course of the vessel lesion, etc. In many situations the global risk of cerebrovascular events is related to a combination of the two abovementioned mechanisms, because in a territory with an hemodynamic failure, also the clearance of emboli is worse (Caplan L et al. 1998). Ultrasound techniques are suitable to identify carotid lesions and there are several studies in the literature, comparing ultrasound techniques with neuroradiological techniques, but they were conducted mainly in a non acute setting. Very few studies or case series are published, using both neuroradiological and neurosonological techniques, in the setting of acute stroke, and the main target of these studies was the intracranial disease. Therefore we are somewhat obliged to translate the reliability data of the non acute phase to the acute phase. This process is make easier by the high accuracy of neurosonological grading of carotid stenosis in a symptomatic patient (Chapell F et al., 2009; Wardlaw et al. 2006).

The overall accuracy of ultrasound examination of the internal carotid artery versus neuroradiological techniques was the subject of several studies and the following figure (from Wardlaw et al. 2006, modified) shows the results of a meta-analysis of them for the 70- 99% range with the NASCET system.


DUS: Doppler UltraSound

260 Neuroimaging for Clinicians – Combining Research and Practice

techniques, Transcranial Doppler (TCD) and Transcranial Colour Coded Duplex Sonography (TCCS). Both these tools are safe, reliable, bedside executable, fast, not expensive and repeatable. Because of these advantages, neurosonology represents an ideal tool to diagnose patients with a focal neurological deficit of suspected vascular origin, particularly in an emergency setting. Furthermore the repeatability and the safety make transcranial Doppler the most suitable tool for monitoring the recanalization, both during a

In the following sections mainly TCCS will be mentioned and discussed, first because of the undeniable advantage of the B-mode visualization of the brain structures and vascular landmarks, and second because the expertise of our group with this technique and the related literature contributes. In a similar manner our attention will be focused on the

**2. Ultrasound examination of cerebroafferent vessels: Extracranial carotid** 

Subtraction Angiography (DSA) is considered the gold standard.

**2.1 Atherosclerotic carotid stenoocclusion** 

Ultrasound examination of the extracranial carotid artery (common and internal carotid artery) is a useful and standardized technique and it represents, in patients with a focal neurological symptom, the ideal screening tool for the identification of carotid stenosis and occlusion and the selection of lesions amenable to surgical or endovascular treatment. Atherosclerosis is a relevant cause of transient ischemic attack and stroke, but also non atherosclerotic conditions, like spontaneous cervical artery dissection and arteritis, can be diagnosed and followed-up. In acute stroke patients the involvement of the extracranial carotid axis is the cause of the cerebrovascular event quite in 18%, being the majority of vessel lesions in the intracranial circulation and sometimes both in extracranial and intracranial circulation (Malferrari G et al. 2007). For both atherosclerotic and nonatherosclerotic diseases, the ultrasound findings and the diagnostic criteria has been compared to the neuroradiological findings and criteria in the literature, whereas Digital

Atherosclerotic involvement of the extracranial carotid artery is not the main cause of vascular lesions in acute stroke patients. It has been reported in about 18% of patients in a 6 hours time window, whereas the intracranial large vessel stenoocclusion accounts for 52.8%. There are two main mechanisms by which the carotid atherosclerotic disease may lead to cerebral infarction: first, an embolic mechanism, as an artery to artery embolism from the plaque rupture; second, an hemodynamic mechanism, because of the blood flow reduction downstream the stenoocclusion. The first one is linearly related to the severity of the carotid stenosis, increasing as the stenosis increases, but the second one is not related to the severity of the stenosis and it depends on multiple factors, as the cerebrovascular reserve, the collateral circulation failure, the time course of the vessel lesion, etc. In many situations the global risk of cerebrovascular events is related to a combination of the two abovementioned mechanisms, because in a territory with an hemodynamic failure, also the clearance of emboli is worse (Caplan L et al. 1998). Ultrasound techniques are suitable to identify carotid lesions and there are several studies in the literature, comparing ultrasound techniques with neuroradiological techniques, but they were conducted mainly in a non acute setting. Very few studies or case series are published, using both neuroradiological and neurosonological

thrombolytic treatment and spontaneously.

anterior circulation stroke.

**axis** 

CTA: Computed Tomography Angiography

MRA: Magnetic Resonance Angiography

CEMRA: Contrast Enhanced Magnetic Resonance Angiography

Fig. 1. Sensitivity and specificity for the diagnosis of a severe carotid stenosis (ultrasound versus neuroradiological techniques) of non-invasive diagnostic techniques compared to DSA

In the acute setting, even more than in a post-acute management, the main objective is the diagnosis or the exclusion of carotid lesion amenable to surgical or endovascular treatment, according to the current guidelines. Therefore it is relevant to assess the reliability of ultrasound techniques for 70-99% stenosis. In the above cited meta-analysis 41 studies (2541 patients, 4876 arteries) from 1980 to 2004 were included, comparing non-invasive imaging with intra-arterial angiography. The conclusion of this meta-analysis agrees with the common clinical practice of using first-line non-invasive tests, as DUS, for diagnosing 70– 99% stenosis. For lesser degrees of stenosis (50–69%) the accuracy of non-invasive techniques is not so high, but again, if surgical indication is well documented for symptomatic carotid stenosis > 70%, the benefit is discussed and very narrow, also for high risk patients, for lesser degrees of stenosis. This categorization is internationally made using the angiographic NASCET grading system (NASCET coll. 1991) and non-invasive imaging techniques should have validated their diagnostic and grading criteria versus the NASCET system.

The ultrasound grading criteria were stated in the Consensus Conference of American Academy of Radiology in 2003 (Grant et al. 2003), but neuroradiological techniques have less shared criteria, based on caliper measurements and ratios, rather than the subjective visual impression. Unfortunately, an implementation of their use in the clinical practice, outside the clinical trials and the evaluation of a central reader, is needed, because the visual impression could be useful only for excluding very tight stenosis, but not for achieving a precise grading (U-King-Im et a. 2007).

Neurosonological Evaluation of the Acute Stroke Patients 263

If there is a significant hemodynamic finding in carotid arteries in patients with acute stroke within 6 hours, it would be often an acute carotid occlusion or a near occlusion. An acute carotid occlusion may occur for the acute complication of a plaque rupture, as a thrombus above the plaque, regardless the previous presence of a mild stenosis, considering only atherosclerosis. The cause of an acute carotid occlusion may be atherosclerosis, cardiac embolism or dissection, because a carotid plaque is not always clearly detectable. Another possibility is the downstream extension of a thrombus in the petrous or intracranial segment of the internal carotid artery, e.g. from an acute complication of intracranial atherosclerosis. The follow-up of the vessel lesion, if surgically or endovascular untreated, can help to define the diagnosis, because time, morphology and rate of recanalization vary, depending on the

Near occlusion is defined as a stenosis in the range 95-99% with distal reduction of vessel size and flow limitation, typically without the increase of flow velocity of the lesser degrees

4a ICA stenosis in power mode; 4b ICA stenosis with the flow waveform; 4 c corresponding 3D reconstruction from CTA; 4d ICA occlusion with hypoechoic luminal thrombus in transverse scanning at the carotid bifurcation (ECA in blue); 4 e corresponding longitudinal scanning in B-mode with the highly hyperechoic plaque and the superimposed organized thrombus; 4g corresponding MRA with the

Finally, the ultrasound examination of carotid artery allows to recognize an indirect sign of the hemodynamic involvement of the petrous and/or intracranial segment of the same artery. Indeed, if a middle cerebral artery stenosis or occlusion does not lead to changes in the upstream flow of the carotid artery, because of the distribution of the resistances in the polygon of Willis, a severe stenosis or occlusion of the intrapetrous segment of the internal carotid artery or at the siphon level, has an identifiable consequence on the waveform of the internal carotid artery, as decreased systolic and diastolic flow velocities, increased systolicdiastolic ratio of the flow velocity, and disappearance of the diastolic component of velocity waveform, depending of the increased resistance to the flow downstream. The more

Fig. 4. Ultrasound hemodynamic findings of the extracranial carotid axis.

of stenosis (Bartlett et al. 2006; Thanvi and Robinson 2007).

cause of the occlusion.

lacking ICA (red asterisk).

In the next figures the grading systems of carotid stenosis and the ultrasound diagnostic criteria are shown.

ICA: internal carotid artery ECA: external carotid artery ECST: European Carotid Surgery Trial NASCET: North American Symptomatic Carotid Endarterectomy Trial CC: Common Carotid

Fig. 2. Schematic drawing of the grading systems of carotid stenosis (NASCET system in the red box)


Fig. 3. DUS criteria from Grant et al. 2003. These criteria have a 92% sensitivity and a 97% specificity for diagnose a carotid stenosis > 70%

In acute stroke evaluation the finding of a severe carotid stenosis should raise the question of identifying intracranial artery-to-artery embolization as a tandem lesion, in large or small vessels. Sometimes the intracranial occlusion can be missed by imaging, both for spontaneous recanalization and spreading of the clot fragments in the distal vessels, and for the very distal localization, witnessed by the localization of infarcts in the distal cortex of the cerebral hemispheres or in the gray-to white matter junction.

In the next figures the grading systems of carotid stenosis and the ultrasound diagnostic

Fig. 2. Schematic drawing of the grading systems of carotid stenosis (NASCET system in the

**STIMA PLACCA (%)**

None < 50 > 50 > 50 Visible

**PRIMARY CRITERIA ADDITIONAL CRITERIA**

< 2 < 2 2-4 > 4 Variable

**ICA/CCA PSV ratio**

**ICA EDV (cm/sec)**

Not applicable

< 40 < 40 40-100 > 100 Variable

Not applicable

Fig. 3. DUS criteria from Grant et al. 2003. These criteria have a 92% sensitivity and a 97%

Visible, lumen not detectable

In acute stroke evaluation the finding of a severe carotid stenosis should raise the question of identifying intracranial artery-to-artery embolization as a tandem lesion, in large or small vessels. Sometimes the intracranial occlusion can be missed by imaging, both for spontaneous recanalization and spreading of the clot fragments in the distal vessels, and for the very distal localization, witnessed by the localization of infarcts in the distal cortex of the

criteria are shown.

CCA: commobn carotid artery ICA: internal carotid artery ECA: external carotid artery

CC: Common Carotid

red box)

**DEGREE OF STENOSIS**

Normal < 50% 50-69% > 70% Near occlusion

Occlusion

ECST: European Carotid Surgery Trial

specificity for diagnose a carotid stenosis > 70%

**ICA PSV (cm/sec)**

High, low or not detectable Not detectable

< 125 < 125 125-230 > 230

cerebral hemispheres or in the gray-to white matter junction.

NASCET: North American Symptomatic Carotid Endarterectomy Trial

If there is a significant hemodynamic finding in carotid arteries in patients with acute stroke within 6 hours, it would be often an acute carotid occlusion or a near occlusion. An acute carotid occlusion may occur for the acute complication of a plaque rupture, as a thrombus above the plaque, regardless the previous presence of a mild stenosis, considering only atherosclerosis. The cause of an acute carotid occlusion may be atherosclerosis, cardiac embolism or dissection, because a carotid plaque is not always clearly detectable. Another possibility is the downstream extension of a thrombus in the petrous or intracranial segment of the internal carotid artery, e.g. from an acute complication of intracranial atherosclerosis. The follow-up of the vessel lesion, if surgically or endovascular untreated, can help to define the diagnosis, because time, morphology and rate of recanalization vary, depending on the cause of the occlusion.

Near occlusion is defined as a stenosis in the range 95-99% with distal reduction of vessel size and flow limitation, typically without the increase of flow velocity of the lesser degrees of stenosis (Bartlett et al. 2006; Thanvi and Robinson 2007).

4a ICA stenosis in power mode; 4b ICA stenosis with the flow waveform; 4 c corresponding 3D reconstruction from CTA; 4d ICA occlusion with hypoechoic luminal thrombus in transverse scanning at the carotid bifurcation (ECA in blue); 4 e corresponding longitudinal scanning in B-mode with the highly hyperechoic plaque and the superimposed organized thrombus; 4g corresponding MRA with the lacking ICA (red asterisk).

Fig. 4. Ultrasound hemodynamic findings of the extracranial carotid axis.

Finally, the ultrasound examination of carotid artery allows to recognize an indirect sign of the hemodynamic involvement of the petrous and/or intracranial segment of the same artery. Indeed, if a middle cerebral artery stenosis or occlusion does not lead to changes in the upstream flow of the carotid artery, because of the distribution of the resistances in the polygon of Willis, a severe stenosis or occlusion of the intrapetrous segment of the internal carotid artery or at the siphon level, has an identifiable consequence on the waveform of the internal carotid artery, as decreased systolic and diastolic flow velocities, increased systolicdiastolic ratio of the flow velocity, and disappearance of the diastolic component of velocity waveform, depending of the increased resistance to the flow downstream. The more

Neurosonological Evaluation of the Acute Stroke Patients 265

5a-c are images from the same patient; B-mode (a) and Power-mode (b) longitudinal scanning of ICA with a mural hematoma (white asterisk) without hemodynamic consequences (flow waveform in c). 5d:

Ultrasound techniques are also suitable for the monitoring of recanalization in patients with carotid artery dissection, because this disease has an highly dynamic course and it is possible, during days and weeks, to image both recanalization and reocclusion or pseudoaneurysmal evolution (fig. 6). In a recent study (Nedeltchev et al 2009), of 268 spontaneous internal carotid artery dissections the vessel hemodynamics at presentation was: 7.5% with 50% stenosis, 11.6% with 51% to 80% stenosis, 34.3% with 81% to 99% stenosis, and 46.6% with an occlusion. The sonological follow-up showed normal findings (complete healing of the vessel without residual signs of the dissection on the wall) in 60%, 50% stenosis in 10%, 51% to 80% stenosis in 1%, 81% to 99% stenosis in 10%, and occlusion in 19% of the vessels.

Fig. 6. Pseudo-aneurysmal evolution of a spontaneous internal carotid artery dissection. In the left side Power-mode longitudinal scanning of distal ICA with a partially thrombosed wall enlargement; in the right side corresponding waveform with a minor focal flow

intimal flap (red asterisk) at the carotid bulb.

acceleration (aliasing in the Colour-mode)

Fig. 5. Direct ultrasound findings of carotid dissection.

characteristic finding of this situation is the so-called "stump flow" in the extracranial internal carotid artery. A summary of the main ultrasound hemodynamic findings is shown in the fig. 4, compared to neuroradiological imaging.

### **2.2 Carotid dissection**

Another cause of stroke, mainly in young patients, is the arterial dissection. It can occur both in extracranial and in intracranial arteries, it is frequently spontaneous and it can start from the intimal or from the adventitial layer of the vessel wall. In the first case the more frequent evolution is a carotid stenosis or occlusion and a potential cerebral damage due not only to hemodynamic factors, but also to artery-to-artery embolism from the clot superimposed on the intimal interruption; in the second case there is a greater likelihood of pseusoaneurysmal evolution with or without rupture (Fusco and Harrigan 2011). Even in a spontaneous dissection, it is often reported a history of trivial or repetitive trauma (1/4 of cases). The gold standard for diagnosis is DSA, but often, when the vessel is partially involved or the mural hematoma is not hemodynamic, magnetic resonance angiography with T2 weighed sections and fat suppression can be almost as much sensitive than DSA. The role of ultrasound examination is discussed, because of the missing petrous carotid segment and of the inability to image or find indirect signs of non-hemodynamic intracranial arterial lesions. The extracranial internal carotid artery is well imaged by ultrasound and therefore a pathologic process is well detectable, if it is located at the carotid bulb and at the origin of internal carotid artery. Unfortunately, a spontaneous extracranial carotid dissection occurs more frequently in the distal segment of the internal carotid artery and sometimes a focal, partial, non-hemodynamic process can be missed by ultrasound examination (Goyal and Derdeyn 2009). Therefore for a reliable evaluation of the sensitivity and specificity of colourcoded duplex ultrasound diagnosis of carotid dissection, it should be taken into account that two different subpopulations exist:



In the second group, where partial non-hemodynamic arterial lesions are often present, the reliability of ultrasound technique is lower. In patients with isolated Horner syndrome nearly 1/3 of spontaneous internal carotid artery dissection does not have any hemodynamic sign, and therefore was missed by ultrasound (Arnold et al. 2008). Considering both hemodynamic and direct signs, the sensitivity of ultrasound for diagnosis of spontaneous internal carotid artery dissection reaches 90% (Alecu et al. 2007).

In an ultrasound semeiological approach, direct signs of a vessel dissection are the visualization of the intimal flap and/or the intramural hematoma; indirect signs are the hemodynamic relevance of the vessel disease, as stenosis without significant atheromatosis and occlusion by acute thrombosis, or signs of distal stenoocclusion from the flow waveform, as stump flow. Unfortunately the identification of a intimal flap or an intramural hematoma is not a frequent finding, although diagnostic of the dissection (fig. 5).

characteristic finding of this situation is the so-called "stump flow" in the extracranial internal carotid artery. A summary of the main ultrasound hemodynamic findings is shown

Another cause of stroke, mainly in young patients, is the arterial dissection. It can occur both in extracranial and in intracranial arteries, it is frequently spontaneous and it can start from the intimal or from the adventitial layer of the vessel wall. In the first case the more frequent evolution is a carotid stenosis or occlusion and a potential cerebral damage due not only to hemodynamic factors, but also to artery-to-artery embolism from the clot superimposed on the intimal interruption; in the second case there is a greater likelihood of pseusoaneurysmal evolution with or without rupture (Fusco and Harrigan 2011). Even in a spontaneous dissection, it is often reported a history of trivial or repetitive trauma (1/4 of cases). The gold standard for diagnosis is DSA, but often, when the vessel is partially involved or the mural hematoma is not hemodynamic, magnetic resonance angiography with T2 weighed sections and fat suppression can be almost as much sensitive than DSA. The role of ultrasound examination is discussed, because of the missing petrous carotid segment and of the inability to image or find indirect signs of non-hemodynamic intracranial arterial lesions. The extracranial internal carotid artery is well imaged by ultrasound and therefore a pathologic process is well detectable, if it is located at the carotid bulb and at the origin of internal carotid artery. Unfortunately, a spontaneous extracranial carotid dissection occurs more frequently in the distal segment of the internal carotid artery and sometimes a focal, partial, non-hemodynamic process can be missed by ultrasound examination (Goyal and Derdeyn 2009). Therefore for a reliable evaluation of the sensitivity and specificity of colourcoded duplex ultrasound diagnosis of carotid dissection, it should be taken into account that


In the second group, where partial non-hemodynamic arterial lesions are often present, the reliability of ultrasound technique is lower. In patients with isolated Horner syndrome nearly 1/3 of spontaneous internal carotid artery dissection does not have any hemodynamic sign, and therefore was missed by ultrasound (Arnold et al. 2008). Considering both hemodynamic and direct signs, the sensitivity of ultrasound for diagnosis

In an ultrasound semeiological approach, direct signs of a vessel dissection are the visualization of the intimal flap and/or the intramural hematoma; indirect signs are the hemodynamic relevance of the vessel disease, as stenosis without significant atheromatosis and occlusion by acute thrombosis, or signs of distal stenoocclusion from the flow waveform, as stump flow. Unfortunately the identification of a intimal flap or an intramural

of spontaneous internal carotid artery dissection reaches 90% (Alecu et al. 2007).

hematoma is not a frequent finding, although diagnostic of the dissection (fig. 5).

in the fig. 4, compared to neuroradiological imaging.

**2.2 Carotid dissection** 

two different subpopulations exist:

al. 2006).

5a-c are images from the same patient; B-mode (a) and Power-mode (b) longitudinal scanning of ICA with a mural hematoma (white asterisk) without hemodynamic consequences (flow waveform in c). 5d: intimal flap (red asterisk) at the carotid bulb.

Fig. 5. Direct ultrasound findings of carotid dissection.

Ultrasound techniques are also suitable for the monitoring of recanalization in patients with carotid artery dissection, because this disease has an highly dynamic course and it is possible, during days and weeks, to image both recanalization and reocclusion or pseudoaneurysmal evolution (fig. 6). In a recent study (Nedeltchev et al 2009), of 268 spontaneous internal carotid artery dissections the vessel hemodynamics at presentation was: 7.5% with 50% stenosis, 11.6% with 51% to 80% stenosis, 34.3% with 81% to 99% stenosis, and 46.6% with an occlusion. The sonological follow-up showed normal findings (complete healing of the vessel without residual signs of the dissection on the wall) in 60%, 50% stenosis in 10%, 51% to 80% stenosis in 1%, 81% to 99% stenosis in 10%, and occlusion in 19% of the vessels.

Fig. 6. Pseudo-aneurysmal evolution of a spontaneous internal carotid artery dissection. In the left side Power-mode longitudinal scanning of distal ICA with a partially thrombosed wall enlargement; in the right side corresponding waveform with a minor focal flow acceleration (aliasing in the Colour-mode)

Neurosonological Evaluation of the Acute Stroke Patients 267

clinical indications for TCCS are basically the same of TCD for imaging of large intracranial vessels, but TCCS has the clear advantage to image the brain parenchyma and the intracranial structures, allowing also the application in neurodegenerative disease (mainly extrapiramidal disorders), the diagnosis and monitoring of hemorrhagic parenchymal transformation after treatment, the perfusional evaluation of the microcirculation, etc. The sensitivity and specificity of TCCS is not lesser than the ones of TCD and the established

In a recent systematic review (Alexandrov et al. 2010) of TCD application, for patients with acute ischemic symptoms in anterior or posterior circulation who had cranial CT or MRI, the authors stated that "TCD can identify patients with proximal arterial occlusions both in anterior and posterior circulation who have the worst prognosis and can benefit the most

Neurosonological tools, both TCD and TCCS are reliable and useful in acute stroke patients and have several comparative studies with MRA, CTA or DSA. The advantage of






Disadvantages are mainly the operator-dependency, but it is notable that all diagnostic techniques somewhat depend on technical skills and expertise of operators, as documented by the intraoperator discordance in grading an extracranial carotid artery stenosis on NASCET study. The early diagnosis of a large vessel occlusion has a great impact on the prognosis of patient and on the choice of the proper treatment. Also in studies with an extended time window for thrombolysis up to 9 hours, because of the mismatch evaluation, only patients with residual large vessel occlusion shown a positive response to treatment and a significant improvement of disability scores (Hacke et al. 2009). Similarly persisting occlusions after reperfusion treatment have worse outcome and this information could be useful to address patients to intra-arterial clot removal or, in some cases, hemicraniectomy. Sensitivity and specificity of neurosonological diagnosis of intracranial steno-occlusion is

eligible patients had a proximal occlusion on TCD (Alexandrov et al. 1999)

determine stroke pathogenesis, in addiction to DSA (Alexandrov et al. 1999)

select patient for a rescue strategy (Saqqur et al. 2005)

very high also compared to DSA (Sloan et al. 2004) (Fig. 8)

indication for TCD in acute stroke are also applicable to TCCS.

from intravenous thrombolysis or rescue intraarterial therapies".

**3.1 Advantages and limitations of neurosonology** 

neurosonology in this setting are:

minutes (Alexandrov et al. 1999)

al. 2006)



The serial ultrasound examination allowed to define the timing of recanalization: indeed the rate of complete recanalization was 16% at 1 month, 50% at 3 months, and 60% at 6 and 12 months. Therefore the recanalization process occurs mainly within the first six months, regardless the treatment. The main factor that was related to a reduced recanalization rate, was an initial occlusion of the dissected vessel, whereas the absence of stroke symptoms and the presence of local manifestations and signs as the unique clinical presentation, were associated with an increased rate of complete recanalization.
