Basilar Artery Thrombosis Workup

Updated: Oct 18, 2017
  • Author: Salvador Cruz-Flores, MD, MPH, FAHA, FCCM, FAAN, FACP, FANA; Chief Editor: Helmi L Lutsep, MD  more...
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Workup

Approach Considerations

The primary goals of the workup are to (1) establish the type of vascular lesion and the mechanism of the stroke and, if early enough, (2) establish whether acute intervention is needed to achieve recanalization.

The laboratory workup should include the following:

  • Complete blood count (CBC)
  • Electrolyte values
  • Blood urea nitrogen (BUN) and creatinine determination
  • International normalized ratio (INR)
  • Prothrombin time (PT) and activated partial thromboplastin time (aPTT)
  • Lipid profile

Young patients (< 45 y) or patients with no evidence of atherosclerosis should be investigated for the presence of procoagulant conditions. However, these tests may need to be repeated several weeks after the acute event to establish whether the abnormality was a response to the acute event or an actual abnormality. These patients are typically screened for the following procoagulant conditions:

  • Protein C, protein S, and antithrombin III deficiencies, especially if the patients has evidence of paradoxical embolism, because these disorders have a stronger association with venous rather than arterial thrombosis
  • Lupus anticoagulant and anticardiolipin antibodies
  • Homocysteine level

Creatine kinase levels, cardiac isoenzyme values, and troponin levels should be tested in the following:

  • All symptomatic patients - Eg, those with chest pain
  • Patients with electrocardiographic evidence of ischemic changes - These patients should be tested because of the high incidence of concomitant coronary artery disease in patients with cerebrovascular disease
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CT Scanning of the Head

Computed tomography (CT) scanning is usually the first imaging study performed. [6] It has a sensitivity of greater than 95% for identifying hemorrhage within the first 24 hours of onset and helps to exclude intra- or extra-axial hemorrhage.

However, CT scanning has a low sensitivity for early ischemia and usually has the disadvantage of significant artifacts caused by the bony structures surrounding the brainstem and cerebellum.

Helpful findings include infarcts in the thalamus and/or occipital lobe or lobes, which indicate involvement of the rostral basilar artery; a hyperdense basilar artery, which indicates probable occlusion [7] ; and a dilated vertebral and/or basilar artery, which indicates a dolichoectatic vessel. (See the image below.) [8]

Spiral CT angiography is helpful in identifying occluded and dolichoectatic vessels. CT angiogram should be helpful in assisting treatment decision making. (See the image below.) [9]

Hyperdense basilar artery (arrow). Hyperdense basilar artery (arrow).
Spiral CT angiography showing occluded basilar art Spiral CT angiography showing occluded basilar artery.

Functional outcome score

The posterior circulation Acute Stroke Prognosis Early CT Score (pc-ASPECTS) with CT Angiography Source Images (CTASI) is a predictive scale of functional outcome in patients with basilar artery thrombosis.

Pc-ASPECTS allocates 10 points to the posterior circulation. One point each is subtracted for hypoattenuation on CTASI in the left or right thalamus, cerebellum, or posterior cerebral artery territory, respectively, and 2 points each are subtracted for hypoattenuation on CTASI in any part of the midbrain or pons. A pc-ASPECTS score of 10 indicates absence of visible posterior circulation ischemia; a score of 0 indicates hypoattenuation in all pc-ASPECTS territories.

The CTASI pc-ASPECTS score can identify patients with basilar artery thrombosis who will have a poor clinical outcome despite recanalization. [10]

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MRI and MRA

Magnetic resonance imaging (MRI) and MR angiography (MRA) are more sensitive than CT scanning for identifying ischemia and vascular occlusion. [6]

Gradient echo technique, with its higher sensitivity for identifying blood, and diffusion/perfusion-weighted images, with their higher sensitivity for identifying ischemia and hypoperfusion, make MRI a more powerful tool for the treatment of patients with basilar artery occlusion. (See the image below.) [11]

Diffusion-weighted MRI images showing a right cere Diffusion-weighted MRI images showing a right cerebellar infarct.

Helpful findings include lesions that suggest microbleeds, tumors, vertebral/basilar dolichoectasia, and vertebral/basilar dissections.

MRA can identify vertebral/basilar occlusion with sensitivity of as high as 97% and a specificity of 98%. (See the image below.)

Magnetic resonance angiography demonstrating the a Magnetic resonance angiography demonstrating the absence of flow in the vertebrobasilar system.

MRA has limitations, however, because it frequently overestimates the degree of stenosis. Severe stenosis may resemble vascular occlusion. This occurs because the image of the vessel with MRA is a flow-related phenomenon; therefore, severe stenosis with significant flow compromise may result in poor visualization of the vessel.

DWI lesion score

A baseline brainstem diffusion-weighted imaging (DWI) lesion score can be used as an independent predictor for clinical outcome in patients with basilar artery thrombosis. [12]

The total number of brainstem arterial territories with abnormal DWI defines the brainstem DWI lesion score, which ranges between 0 and 22. A score of 0 indicates absence of visible posterior circulation ischemia; a score of 22 indicates DWI restriction in the entire brainstem. [12]

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Ultrasonography

Transcranial Doppler (TCD) ultrasonography is a useful tool for evaluating cerebrovascular disease; however, it is often inaccurate. In patients with basilar artery disease, the reported sensitivity is 72% and the specificity is 94%. TCD ultrasonography is helpful in follow-up once an initial evaluation has demonstrated the lesion.

The flow direction detected by TCD ultrasonography, in combination with CT angiography, may be useful before performing invasive angiography, to help predict the area of stenosis or occlusion. [13]

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Electrocardiography and Echocardiography

Electrocardiography

Electrocardiography (ECG) should be performed in all patients during the initial evaluation because it can reveal paroxysmal arrhythmias such as atrial fibrillation. Additionally, the prevalence of coronary disease is high in patients with cerebrovascular disease.

Ischemic changes seen on ECG should be investigated further with serum creatine kinase measurements, cardiac isoenzyme profiles, and/or troponin levels for the following reasons:

  • Of patients with acute stroke, 5-20% have an arrhythmia.
  • Additionally, 2-3% have a myocardial infarction.
  • The presence of arrhythmias (eg, atrial fibrillation) has an impact on the long-term management plan for stroke prevention

Echocardiography

Echocardiography should be considered in all patients because cardioembolism is frequent enough in this population to warrant such consideration. Moreover, even patients with documented atherothrombosis may have a concomitant cardiac source of embolism.

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Catheter Angiography

With the availability of noninvasive imaging modalities such as MRI, MRA, and TCD ultrasonography, the role of angiography has changed; however, it still is considered the criterion standard. Angiography is performed (1) when MRA cannot be performed because the patient has an absolute contraindication, such as a pacemaker, or (2) when the quality of noninvasive studies is not satisfactory or the results of other tests do not explain clinical findings. (See the images below.)

Right vertebral artery angiography showing an occl Right vertebral artery angiography showing an occlusion with no flow in the basilar artery.
Angiography performed after intra-arterial thrombo Angiography performed after intra-arterial thrombolysis and angioplasty showing recanalization and perfusion of the basilar artery and its branches.

Angiography should be pursued as a first-line diagnostic test after CT scanning and once the decision is made that recanalization should be performed.

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