Approach Considerations
Reviewing documentation and performing baseline neurologic examinations help the clinician to recognize an evolving or recurring stroke, which is treatable, from a completed infarction.
After stroke has been correctly identified and localized, the next step is to determine the mechanism by which the stroke occurred, as this will guide long-term preventive strategies. In some cases, all diagnostic possibilities need to be considered and the workup is extensive.
In other cases, however, the mechanism may be promptly suggested by the patient’s history, with a focused work-up revealing an immediate cause. An example would be a young individual with neck trauma in whom vascular imaging demonstrates a cervical artery dissection with thrombosis.
Essential components of workup in posterior cerebral artery (PCA) stroke depend on the patient's age, stroke risk factors, and prior medical history. For example, studies used to evaluate the older patient (whose stroke is associated with cardiovascular disease) may include those that assess (1) severe anemia or volume depletion that can cause, worsen, or confound cerebral ischemia; (2) early infection as a result of aspiration; and (3) baseline coagulation status in case treatment involves heparin, warfarin, or thrombolysis.
Strokes occurring in persons younger than 50 years require investigation for etiologies such as cardiac defects (patent foramen ovale), thrombophilia or hypercoagulable state (protein S or C or antithrombin III deficiency, activated protein C resistance, G20210A prothrombin mutation), arterial dissection, connective-tissue autoimmune disorders (antiphospholipid syndrome), and malignancy.
Identification of other stroke risk factors, including hypertension, diabetes, elevated cholesterol and lipid panels, and hyperhomocysteinemia, is also useful.
Evaluate patient's swallow function so that diet can be modified appropriately and aspiration pneumonia avoided.
Imaging
Imaging modalities that can be employed in the diagnosis and evaluation of PCA strokes include computed tomography (CT) scanning, CT angiography (CTA), single-photon emission CT (SPECT) scanning, magnetic resonance imaging (MRI), and MR angiography (MRA). Positron emission tomography (PET) scanning can be used to analyze neurometabolism in vivo; it is at present a research tool.
Laboratory Studies
In the acute phase, routine blood tests should include a complete blood count (CBC), prothrombin time (PT)/activated partial thromboplastin time (aPTT)/international normalized ratio (INR), electrolytes, creatinine, and serum glucose. These tests are a part of the stroke mechanism work-up and are required to assess whether the patient is a candidate for acute stroke therapies.
When the mechanism of stroke is atherosclerotic disease, additional blood tests should be performed to assess atherosclerotic risk factors. Diabetes screening should be performed. A fasting serum cholesterol profile should be obtained.
Hypercoagulable disease workup
If the stroke mechanism is not evident from the medical history and routine workup, then special hematologic and serologic examinations should be considered, particularly in young patients with cryptogenic stroke. A full hypercoagulable workup should include assays for arterial thrombophilia, including antiphospholipid antibodies and lupus anticoagulant.
Additional assays for venous thrombosis may be obtained in the appropriate clinical setting (ie, patent foramen ovale with paradoxical embolism) and include protein C, protein S, factor V Leiden/activated protein C resistance, antithrombin III, and prothrombin gene polymorphism. Some of these assays give abnormal results in the setting of acute stroke or anticoagulant medications and may need to be obtained on a delayed basis. The use and value of hypercoagulable disorder assessments remains a somewhat imprecise and controversial area of stroke neurology.
CT Scanning
All patients with suspected stroke should undergo emergent neuroimaging with CT scanning or MRI. An unenhanced head CT scan is usually performed, as this test is widely available, can be rapidly obtained, and is sensitive in identifying intracranial hemorrhage. (See the images below.)
Unenhanced head computed tomography (CT) scan demonstrating a subacute L posterior cerebral artery (PCA) infarct.
Unenhanced head computed tomography (CT) scan demonstrating hemorrhagic conversion of an ischemic stroke, approximately 72 hours after symptom onset.
An emergent CT or MRI scan is required prior to considering acute stroke therapies, including thrombolysis. CT scanning aids in the following:
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Identifying hemorrhage
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Identifying strokes that may be less acute than reported by patients - Ie, the presence of hypodensity suggests a more subacute than hyperacute process
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Identifying hyperdense vessels
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Excluding alternate diagnoses that may masquerade as stroke - Ie, neoplasm or other masses
CT scanning is less sensitive for lesions in the infratentorial region than the supratentorial region due to bony signal artifact and decreased tissue detail.
CT angiography
In the acute stroke setting, the use of CTA has greatly expanded. CTA can identify extracranial vascular disease (cervical atheromatous disease and dissection) and intracranial disease (intracranial stenosis or embolism). CTA results are frequently used to guide acute and chronic therapies, including medical, surgical, and endovascular treatments.
SPECT scanning
SPECT scanning is a nuclear medicine study using radioisotopes of technetium. It provides an analysis of relative blood flow by region, usually in the resting state. It is rarely useful in the clinical setting of acute stroke and can be considered a research tool.
MRI
MRI produces a much better examination of midbrain, subthalamic, and thalamic structures than CT scanning does. It also identifies acute stroke much earlier than does CT scanning, by highly sensitive, diffusion-weighted imaging. MRI offers various modalities that can aid in determining the age of the stroke, identify multiple or small lesions that would be missed on CT scans, and identify at-risk or penumbral tissue by way of perfusion imaging. (See the image below.)
Brain magnetic resonance imaging (MRI) scan demonstrating acute stroke. Diffusion restriction is seen on diffusion-weighted imaging.
Currently, the use of diffusion/perfusion imaging studies to identify mismatch (suggesting the presence of at-risk brain tissue that is not yet infarcted) is actively being studied, but it is not the accepted standard of care.
MRA is frequently used to assess the extracranial and intracranial vasculature, but it is more prone to artifact and tends to overestimate the degree of hemodynamic compromise within vessels. (See the image below.)
Magnetic resonance (MR) angiogram demonstrating bilateral fetal posterior cerebral artery (PCA) variants (black arrows) with the basilar artery terminating in bilateral superior cerebellar arteries (blue arrows).
Angiography
Catheter cerebral angiography remains the criterion standard for evaluation of vascular anatomy. However, it is a more invasive method and does carry a small risk of procedure-related morbidity.
Increasingly, noninvasive methods of viewing the arterial anatomy (CTA, MRA, transcranial Doppler [TCD] ultrasonography) are being used; each has its own benefits, technical challenges, and limitations. In many cases, these noninvasive methods are sufficient for diagnosis and management. However, when they produce unclear findings or more information is needed about the vascular anatomy, angiography is required. In addition, angiography is required as a precursor to endovascular treatments. (See the images below.)
Digital subtraction angiogram demonstrating an acute L posterior cerebral artery (PCA) occlusion (red arrow) following balloon-assisted coiling of a basilar tip aneurysm.
Digital subtraction angiogram demonstrating revascularization of acute L posterior cerebral artery (PCA) occlusion (red arrow) during a balloon-assisted basilar tip aneurysm revascularization with use of balloon angioplasty.
Specific anatomical features of PCA aneurysms were identified by angiographic study of 81 patients with a diagnosis of 93 PCA aneurysms. In this anatomical study, 53 patients underwent computed tomography angiography, 49 underwent digital subtraction angiography, and 6 underwent magnetic resonance angiography. There were 29 ruptured and 64 unruptured PCA aneurysms. The distribution of the aneurysms along the PCA segments was P1 (N = 39; 9 ruptured), P1/P2 junction (N = 25; 9 ruptured), P2 (N = 21; 5 ruptured), and P3 (N = 8; 6 ruptured). The median aneurysm size was 7 mm for the ruptured aneurysms and 4 mm for the unruptured aneurysms. Saccular aneurysms (N = 69, 74%) had a typical projection for each location: P1 segment, upward (67%); P1/P2 junction, anterior/upward (80%); P2 segment, lateral (67%); and P3 segment, posterior (50%). Multiple aneurysms were seen in 43 patients. PCA aneurysms related to arteriovenous malformations were observed in 10 patients. [11]
Ultrasonography
TCD ultrasonography is not widely used in acute stroke; however, it may become useful as an adjunct in the diagnosis and acute treatment of stroke. TCD ultrasonography is dependent on the skill and experience of the operator. In skilled hands, the distal basilar and P1 and P2 segments can be assessed and may detect acute clot in the posterior cerebral artery (PCA).
Carotid duplex ultrasonography may be considered in PCA stroke when a fetal origin PCA is present. In this setting, carotid atheromatous disease would be symptomatic and patients may be considered for carotid endarterectomy or stenting for recurrent stroke prevention.
Echocardiography and Electrocardiography
Echocardiography
Transthoracic echocardiography (TTE) is used routinely to investigate possible cardiac sources of embolus. Transesophageal echocardiography (TEE) is a more sensitive test. It is more effective than TTE at identifying valvular lesions, aortic arch atheroma, and interatrial shunts. Patent foramen ovale and any abnormal anatomy associated with it (such as atrial septal aneurysms) are more frequently detected by TEE.
Electrocardiography
All patients with stroke should have an immediate ECG. ECG may identify stroke mechanisms or stroke-associated conditions, such as myocardial infarction, conduction abnormalities, and atrial fibrillation.
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Unenhanced head computed tomography (CT) scan demonstrating a subacute L posterior cerebral artery (PCA) infarct.
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Unenhanced head computed tomography (CT) scan demonstrating hemorrhagic conversion of an ischemic stroke, approximately 72 hours after symptom onset.
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Brain magnetic resonance imaging (MRI) scan demonstrating acute stroke. Diffusion restriction is seen on diffusion-weighted imaging.
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Magnetic resonance (MR) angiogram demonstrating bilateral fetal posterior cerebral artery (PCA) variants (black arrows) with the basilar artery terminating in bilateral superior cerebellar arteries (blue arrows).
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Digital subtraction angiogram demonstrating an acute L posterior cerebral artery (PCA) occlusion (red arrow) following balloon-assisted coiling of a basilar tip aneurysm.
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Digital subtraction angiogram demonstrating revascularization of acute L posterior cerebral artery (PCA) occlusion (red arrow) during a balloon-assisted basilar tip aneurysm revascularization with use of balloon angioplasty.
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Computed tomography (CT) scan of the brain showing hypodense areas in the right occipital lobe consistent with a recent posterior cerebral artery (PCA) ischemic infarct.
