The diagnostic studies complement the clinical assessment. The initial (emergency) evaluation is performed when a patient with a suspected stroke is fi rst seen. The goals of testing are to establish isch- emia as the cause of the neurological symptoms (and to exclude alternative diagnoses), to screen for acute neurological or medical complications, and to deter- mine the patient’s eligibility for emergency treat- ment with reperfusion therapy. The guidelines delineate the diagnostic tests that need to be avail- able in most community hospitals on a 24-hour per day and 7-day per week basis [3]. The goal is to complete the evaluation within 1 hour of the patient’s arrival in the emergency department (Table 4.8). The additional (optional) tests listed in Table 4.8 may be performed as indicated by the patient’s history, clinical fi ndings, or comorbidities.
Brain imaging is the cornerstone of the evalua- tion; potential fi ndings include the size, location, and vascular territory of the infarction, the presence of intracranial bleeding, or the presence of acute complications such as hydrocephalus or a mass. The tests also provide information about the possible degree of reversible brain ischemia, the status of intracranial arteries, and the hemodynamic status [30]. Brain imaging tests help select patients who might be treated with reperfusion therapies, includ- ing IV tPA, the risk for hemorrhagic complications of treatment, and the presence of arterial occlusions that may be treated with intra-arterial interventions.
The most commonly performed tests are CT and magnetic resonance imaging (MRI). While MRI provides more information on stroke than CT, the treatment of a patient with a suspected ischemic stroke should not be delayed in order to perform an MRI when CT is readily available.
Nonenhanced CT of the brain is recommended for the initial evaluation of most patients [3,31]. CT is noninvasive, and it does provide important infor- mation; the yield in detecting intracerebral hemor- rhage or subarachnoid hemorrhage is very high [32,33]. CT can also detect an intracranial mass such as a tumor or subdural hematoma. In most cases, CT will not demonstrate the acute effects of brain ischemia. The assumption is that acute ischemia is the explanation of a patient’s focal neurological Table 4.6 Patterns of neurological impairment subtypes of
ischemic stroke
Multilobar hemisphere infarction
Consciousness – alert to drowsy (subsequently stupor/coma) Behavioral or cognitive signs are prominent
Right (nondominant) hemisphere – neglect, aprosodia Left (dominant) hemisphere – aphasia, apraxia Contralateral visual fi eld defect
Conjugate eye deviation toward the lesion Dysarthria
Contralateral hemiparesis and sensory loss Motor and sensory impairments usually similar Affect face, arm, and leg
Branch cortical hemisphere infarction Alert
Behavioral cognitive signs are prominent
Right (nondominant) hemisphere – neglect, aprosodia Left (dominant) hemisphere – aphasia, apraxia
Contralateral visual fi eld defect found with posterior infarctions Conjugate eye deviation toward the lesion often mild or absent Dysarthria is uncommon
Contralateral hemiparesis and sensory loss May not affect face, arm, and leg equally Motor and sensory impairments may not be equal Subcortical (lacunar) hemisphere infarction
Alert
Behavioral and cognitive signs less prominent or subtle Right (nondominant) hemisphere – neglect, aprosodia Left (dominant) hemisphere – aphasia, ataxia Contralateral visual fi eld defects are uncommon Dysarthria is common
Contralateral hemiparesis and sensory loss are common Generally affects face, arm, and leg equally May involve motor or sensory loss in isolation Brain stem – cerebellar infarction
Consciousness ranges from alert to coma Behavioral and cognitive signs are absent Visual fi eld defects are absent
Cranial nerve palsies present, ipsilateral to side of lesion Oculorotatory disturbances are prominent
Dysarthria is often severe
Paralysis may be contralateral, bilateral, or crossed Sensory loss may be contralateral, dissociated, or crossed Motor and sensory loss may occur in isolation Prominent ataxia ipsilateral to side of lesion
Table 4.7 Components of the National Institutes of Health Stroke Scale
Level of consciousness Orientation questions (2)
Alert 0 Answers both correctly 0
Drowsy 1 Answers one correctly 1
Stupor 2 Answers neither correctly 2
Coma 3
Response to commands (2) Lateral eye movements
Both tasks correct 0 Normal movements 0
One task performed 1 Partial gaze paresis 1
Performs neither task 2 Complete gaze paresis 2
Visual fi elds Facial movement
No visual fi eld defect 0 Normal facial movement 0
Partial hemianopia 1 Minor facial weakness 1
Complete hemianopia 2 Partial facial weakness 2
Bilateral hemianopia 3 Complete facial palsy 3
Motor function (arm) Motor function (leg)
Both right and left rated independently
No drift 0 No drift 0
Drift before 5 seconds 1 Drift before 5 seconds 1
Falls before 10 seconds 2 Falls before 10 seconds 2
No effort against gravity 3 No effort against gravity 3
No movement 4 No movement 4
Limb ataxia Sensory examination
No ataxia 0 No sensory loss 0
Ataxia in one limb 1 Mild sensory loss 1
Ataxia in two limbs 2 Severe sensory loss 2
Language Articulation
Normal language 0 Normal speech 0
Mild aphasia 1 Mild dysarthria 1
Severe aphasia 2 Severe dysarthria 2
Global aphasia or mute 3
Extinction or inattention (two modalities tested)
Absent 0
Mild loss (one sensory) 1
Severe loss (two sensory) 2
symptoms of sudden and recent onset when a CT is normal and other causes are excluded. Physicians may recognize the subtle early abnormalities that can be demonstrated on CT [34–36]. The fi ndings evolve over the fi rst hours after stroke and include the development of lenticular hypodensity, loss of the gray-white matter differentiation, particularly in the lateral margins of the insula, and sulcal efface-
ment. CT may also demonstrate an acute arterial occlusion, most commonly found in the middle cerebral artery or its branches (dense artery sign and dot sign) (Figure 4.1a and 4.1b). A thrombus may also be found in the basilar artery. These fi ndings are most likely among patients with major multilobar infarctions, and they are associated with poorer out- comes [37]. Focal areas of cortical swelling have
been detected on CT, but this fi nding is not specifi c for cerebral ischemia [38]. There are insuffi cient data to state that any specifi c CT fi nding, other than hemorrhage, disqualifi es a patient for treatment with tPA within 3 hours of stroke onset [3]. Sequen- tial CT studies can be used to monitor for secondary hemorrhagic changes or prior to starting antithrom- botic agents [39].
Dynamic CT perfusion and CT angiography may provide information about cerebral blood fl ow, mean transient time, cerebral blood volume, and vascular status [40,41]. The changes on perfusion CT may be compared with unenhanced CT to iden- tify hypoperfused, but potentially salvageable isch- emic brain (i.e., the ischemic penumbra) [42]. CT angiography is accurate in detecting lesions of major intracranial or extracranial arteries [41,43]. These tests can be done on an emergency basis with the contrast-enhanced studies performed immediately following the traditional unenhanced scan. However, the equipment and professional expertise to perform these tests are not widely available, especially in a community setting. The patient should be screened for renal dysfunction. Some patients are allergic to the contrast agent. In addition, the volume of con- trast is considerable, and it may affect decisions about intra-arterial treatment, which require addi- tional injections of contrast. While the role of Table 4.8 Emergency evaluation of a patient with suspected
ischemic stroke Baseline evaluation
Noncontrast enhanced CT or magnetic resonance imaging of the brain
Complete blood count, platelet count
Coagulation tests (prothrombin time/international normalization ratio and activated partial thromboplastin time)
Blood glucose
Serum electrolytes/renal function tests Electrocardiogram
Markers of myocardial ischemia (troponin) Oxygen (pulse oximetry)
Evaluation in selected patients
Arterial blood gas tests (if hypoxia is suspected) Chest radiogram (if acute heart, aorta, or lung disease is
suspected)
Pregnancy test (women of childbearing potential) Toxicology screen and blood alcohol (if intoxication is
suspected)
Hepatic function tests (if metabolic disorder is suspected) Cerebrospinal fl uid examination (if subarachnoid hemorrhage is
suspected and brain imaging is negative for blood, or if an infl ammatory vasculopathy, i.e., infection or vasculitis, is suspected)
Electroencephalogram (if seizures are suspected)
(a) (b)
Fig. 4.1 (a and b) Axial views of a computed tomographic scan of a patient with an occlusion of the left middle cerebral artery. The scan demonstrates a thrombus in the artery (dense artery sign) (a) and the higher image also demonstrates a thrombus in a distal branch of the middle cerebral artery (dot sign). Images courtesy of Patricia Davis, MD, University of Iowa, Iowa City, IA.
contrast-enhanced CT is likely to increase in the future, current guidelines recommend that treat- ment with tPA should not be delayed in order to obtain these tests [3].
MRI is also useful for the emergency evaluation of patients with suspected stroke. It has several advantages, including the detection of acute, small, and posterior fossa infarctions; differentiation of acute from older infarction; excellent spatial resolu- tion; and detection of arterial occlusions. It also avoids exposure to ionizing radiation. A suggested sequences of studies would include diffusion- weighted imaging (DWI), FLAIR, and gradient-echo sequences done without contrast (Figure 4.2). Sub- sequently, the patient could undergo MRI perfusion imaging that can be obtained with gadolinium con- trast. The perfusion sequences can assess the time to peak, mean transient time, cerebral blood fl ow, and cerebral blood volume. Magnetic resonance angiog- raphy (MRA) of the intracranial and extracranial vasculature may follow; this can include a contrast- enhanced time of fl ight study. MRI can rapidly visu- alize the acute ischemic lesion (particularly with DWI sequences) and occlusions of major intracra- nial arteries [44,45]. A contrast-enhanced study can be performed to assess perfusion to the brain. It does provide some measures of the cerebral hemody- namic status. A comparison of the volume of the
lesions found between DWI and perfusion sequences has been used to help defi ne the ischemic penumbra (i.e., diffusion–perfusion mismatch; Figure 4.3a and 4.3b). MRA can demonstrate severe stenosis or occlusion of the major intracranial or extracranial vasculature [46] (Figure 4.4). Limitations of MRI
Fig. 4.2 Axial diffusion-weighted magnetic resonance image of a patient with an acute ischemic stroke. The scan shows bilateral thalamic and right occipital infarctions.
(a) (b)
Fig. 4.3 (a and b) Axial diffusion-weighted and perfusion magnetic resonance images obtained from a patient with a middle cerebral artery occlusion. The area of ischemia (diffusion-weighted image) is smaller than the area of decreased perfusion (diffusion/perfusion mismatch).
MRI studies may be considered for the evaluation of some patients with acute stroke, but are not required [3].
CT angiography, MRA, transcranial Doppler ultrasonography, carotid duplex, and catheter-based angiography can be used to assess the intracranial and extracranial vasculatures. The latter is often used as part of a procedure that includes intra- arterial administration of a thrombolytic agent or use of a mechanical intervention (Figure 4.5a and 4.5b). These tests are also performed after the patient has been admitted to the hospital, and the results are used in making decisions about the prevention of recurrent stroke.
Electrocardiography, which is a component of the emergency evaluation, is performed to screen for concomitant heart disease including myocardial ischemia and arrhythmias. Besides affecting acute management, the results also infl uence decisions about the prevention of recurrent stroke. Transtho- racic echocardiography or transesophageal echocar- diography is a component of evaluation of a patient with stroke because the results infl uence decisions about long-term prophylaxis against recurrent stroke. The other diagnostic studies outlined in Table 4.9 include assessments for risk factors for premature atherosclerosis and screening for hyper- coagulable disorders or autoimmune diseases.
(a) (b)
Fig. 4.4 Anterior-posterior view of a magnetic resonance angiographic study shows occlusions of the right internal carotid and middle cerebral arteries.
Fig. 4.5 Anterior-posterior view of a cerebral arteriogram demonstrates an occlusion of the middle cerebral artery (a). The second image visualizes distal vasculature after a microcatheter has been passed through the thrombus (b). An embolus is seen in a distal branch artery.
These fi lms were obtained prior to local intra-arterial administration of a thrombolytic agent.
include its cost, relatively limited availability, and contraindications including claustrophobia, cardiac pacemakers, and metal implants. Nephrogenic sys- temic fi brosis has been associated with gadolinium used for enhanced MRI studies, and patients’ renal function should be screened before the agent is given. Current guidelines indicate that multimodal
with frequent measurements of vital signs, pulse oximetry, and neurological status [47]. The goals are to control acute complications and to stabilize the patient so that stroke-specifi c interventions can be prescribed [48].
Protecting the airway with elective intubation is often indicated for patients with decreased level of consciousness, severe bulbar dysfunction, or hypoxia necessitating oxygen supplementation [49–52]
(Table 4.10). Fever following stroke is associated with an increased risk of morbidity or mortality pre- sumably as the result of increased metabolic demands and other cellular consequences of an elevated tem- perature [53,54]. While clinical trials have been inconclusive, lowering the body temperature by antipyretics or cooling devices can be prescribed [55,56]. Induced hypothermia may be neuroprotec- tive, and the utility of this intervention is being tested in the setting of acute stroke. Currently, it is considered to be experimental [57–62]. Serious cardiac arrhythmias are a potential complication;
these should be treated with medications selected on a case-by-case basis [63,64]. Arterial hypotension, secondary to volume depletion, blood loss, or decreased cardiac output may occur. Aortic dissec- tion is rare, but its presence is associated with an increased likelihood of unfavorable outcomes [65].
Treatment includes volume replacement and vaso- pressor agents.
Table 4.9 Additional diagnostic tests for evaluation of a patient with an ischemic stroke
Vascular imaging
Magnetic resonance angiography CT angiography
Carotid duplex ultrasonography Transcranial Doppler ultrasonography Catheter-based arteriography Cardiac imaging
Transthoracic echocardiography Transesophageal echocardiography Cardiac CT
Cardiac magnetic resonance imaging Risk factor evaluation
Fasting lipid profi le
Fasting blood glucose and hemoglobin A1c Coagulation studies
Fibrinogen, fi brin degradation products, d-Dimer Antithrombin
Proteins C and S
Antiphospholipid antibodies and lupus anticoagulant Factor V Leiden
Prothrombin gene mutation
Hemoglobin electrophoresis and sickle-cell preparation Immunological studies
Erythrocyte sedimentation rate C-reactive protein
Antinuclear antibodies
Anticytoplasmic nuclear antibodies
Example Case, cont’d.
Upon return from CT, her blood pressure was 180/105 mm Hg. It was checked on two more occasions, and both measurements showed slightly lower readings. Otherwise, her examination had not changed. She did not receive any
antihypertensive medications.