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772 PART 6: Neurologic Disorders

the posterior fossa) at any time. However, MRI is more cumbersome to Early electrocardiographic (ECG) monitoring detects previously
perform in acutely ill patients because of longer imaging times, the need unsuspected atrial fibrillation in 3% to 5% of patients with acute cerebral
for special nonferromagnetic life support equipment, and the necessity of ischemia. 10-12 This information is clinically useful since the superiority of
putting the entire body in the scanner. Demonstration of cerebral infarc- oral anticoagulation over aspirin for long-term secondary stroke preven-
tion by neuroimaging is rarely necessary, since the diagnosis often can be tion in this circumstance has been demonstrated. There is, however, no
13
made reliably by the clinical presentation of the sudden onset of a focal benefit for immediate anticoagulation in these patients. Transthoracic
14
brain deficit together with a negative CT scan to exclude hemorrhage and echocardiography can provide evidence of poor left ventricular function
other conditions. MRI can be helpful for improving diagnostic certainty and, rarely, left ventricular thrombi. In patients without clinical cardiac
when there is no clear history of an abrupt onset or the localization of the disease (no previous history or signs or symptoms of cardiac disease, no
neurological findings is confusing. Intravenous contrast administration ECG abnormalities, and normal cardiac silhouette on chest x-ray), left
increases the sensitivity for detecting diseases that may mimic stroke, ventricular thrombi are vanishingly rare. Transesophageal echocardiog-
such as tumor, chronic subdural hematoma, and abscess. raphy has made it possible to identify left atrial thrombi and atheroscle-
Diagnosis of border zone infarction due to systemic arterial hypoten- rosis of the ascending aorta. Large aortic arch lesions are associated with
sion is almost entirely dependent on the pattern of infarction shown an increased risk of stroke. The most common lesion detected by echo-
by CT or MRI. Border zone infarctions are often asymmetrical and cardiography in patients with stroke who have no other evidence of heart
patchy; rarely is the entire border zone territory between the middle disease is patent foramen ovale with or without atrial septal aneurysm.
cerebral artery and posterior or anterior cerebral artery involved. Treatment implications are problematic (see below). ECG abnormali-
Furthermore, the actual location of the border zone varies from person ties are extremely common in patients with SAH. However, the clinical
to person. When more than one area of acute infarction has occurred relevance of these abnormalities is questionable since they often do not
4
and all infarcted areas are within the border zones, systemic hypotension correlate with echocardiographic abnormalities, histopathologic abnor-
should be considered as a cause of infarction. malities, or serum markers of cardiac injury. Approximately 20% of
MRI has no advantage over CT in the demonstration of acute intra- patients with SAH have elevated serum troponin-I levels. Patients with
cerebral hemorrhage, but it does have superior sensitivity for detecting elevated troponin-I levels should undergo echocardiography, as elevated
subacute or chronic hemorrhage. MRI with contrast is the most sensitive troponin-I levels have been shown to be 100% sensitive and 86% specific
way to detect a tumor underlying an ICH. Noncontrast CT has a sensi- for the detection of left ventricular dysfunction by echocardiography. 15
tivity of >90% for detecting SAH when performed within 24 hours of Cerebral arteriography provides high-resolution images of both extra-
hemorrhage. There is no role for standard MRI in the initial diagnosis of cranial and intracranial vessels, which may be useful occasionally in the
acute SAH since it is difficult to perform in an acutely ill agitated patient identification of causes of cerebral infarction such as arterial dissection.
and it does not increase the likelihood of detecting SAH. It is of little value for the diagnosis of isolated cerebral vasculitis due to
In the patient who is awake and alert with acute focal brain dysfunc- the high prevalence of both false-positive and false-negative findings.
16
tion and in whom noncerebrovascular causes can be excluded, the imme- Magnetic resonance arteriography (MRA), often overestimates the
diate distinction between cerebral infarction and cerebral hemorrhage degree of stenosis, sometimes even portraying normal vessels as
may not be necessary if no emergent treatment of the stroke is planned. abnormal. In addition, MRA lacks the high resolution of conventional
In certain situations, however, differentiation between infarction and arteriography and cannot be used to exclude small aneurysms or abnor-
hemorrhage may be critical. Patients with ischemic stroke whose time malities in distal arterial branches. In contrast, magnetic resonance
of onset can be determined to be less than 4.5 hours earlier and whose venography has supplanted conventional catheter angiography for the
other medical problems do not preclude thrombolytic therapy, will detection of sagittal and lateral sinus venous thrombosis. In hypertensive
benefit from treatment with intravenous tissue plasminogen activator patients with lobar intracerebral hemorrhage and in nonhypertensive
(t-PA). In this circumstance, emergency CT to exclude cerebral hemor- patients with intracerebral hemorrhage in any location, arteriography
5,6
rhage is imperative (see the section on treatment below). In the patient may demonstrate vascular malformations or aneurysms. CT angiogra-
2
with decreased consciousness and a focal neurologic deficit, emergency phy is almost as sensitive as arteriography for detecting causes of intra-
CT may be critically important in identifying an intracranial tumor or cerebral hemorrhage but will occasionally miss a small arteriovenous
subdural hematoma that requires emergency neurosurgical intervention. malformation or fistula. 17-19 Cerebral arteriography plays an important
Except in patients with cerebral venous thrombosis, hematologic evalu- role in the evaluation of the patient with SAH by confirming the exis-
ation of patients with ischemic stroke is rarely of value. Antiphospholipid tence of an aneurysm and providing the necessary information to plan a
antibodies are found in a high percentage of patients with arterial stroke, surgical approach. If CT or lumbar puncture demonstrates SAH, a four-
but they confer neither a worse prognosis nor is there a benefit of long- vessel angiogram should be performed as soon as possible. A complete
term anticoagulation. Acquired or hereditary hypercoagulable disorders study is necessary to look for multiple aneurysms. If arteriography does
7
have not been clearly linked to arterial ischemic stroke, whereas they are not reveal a cause for SAH, it should be repeated in 1 to 2 weeks.
clearly of etiologic importance in cerebral venous thrombosis. In patients Doppler ultrasound of the carotid arteries is useful to screen for severe
with intracranial hemorrhage, especially in the ICU, acquired hemor- carotid stenosis at the cervical bifurcation in patients who are candidates
rhagic diatheses (eg, anticoagulant or thrombolytic drugs, thrombocyto- for carotid endarterectomy. It is important to remember that the reliabil-
penia) should always be considered and should be sought by appropriate ity of this technique varies from center to center. Patients with transient
laboratory testing when clinical suspicion indicates. ischemic attacks (TIAs) or mild stroke who are good surgical candidates
Lumbar puncture with cerebrospinal fluid (CSF) examination can should be evaluated immediately since the risk of stroke following TIA
be an extremely important test in the evaluation of the patient with can be as high as 1 in 20 within the first 2 days. On the other hand, in
20
apparent stroke, especially in patients with acquired immune deficiency patients with a completed stroke, there is usually no urgency in obtain-
syndrome (AIDS) or when there is infection elsewhere. Meningitis may ing this information since carotid endarterectomy does not play a role
cause stroke by producing thrombosis of arteries or cortical veins. CSF in the management of acute stroke. Transcranial Doppler (TCD) studies
pleocytosis is common following septic embolism from infective endo- can detect stenosis of intracranial vessels, but the value of this informa-
carditis and can serve as a valuable clue to its presence. Lumbar puncture tion in management decisions remains to be demonstrated. TCD can
21
is the most sensitive test for detection of SAH; it should be performed also detect increases in flow velocity in most patients with arteriographic
when there is a strong clinical suspicion and a negative CT scan, or when vasospasm following SAH (see below).
CT is not available or feasible. CSF xanthochromia, which begins to The value of regional cerebral blood flow (CBF) measurements with
develop after 4 hours and is reliably present at 12 to 24 hours, can help positron emission tomography (PET), single photon emission com-
differentiate SAH from traumatic lumbar puncture. 8,9 puted tomography (SPECT), CT, or MRI in the diagnosis and treatment

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