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A 65-year-old man awakened from an afternoon nap and noted a complete hemiparesis involving his arm, face, and leg. His wife called EMS and he was brought to the ED within half an hour.

A noncontrast head CT was obtained immediately after the patient’s arrival (Figure 1). The CT was initially interpreted as normal.

  • On which side was the patient’s hemiparesis?
  • What are the early CT signs of an ischemic stroke?
  • Should thrombolytic agents be administered?

The principal role of CT in patients with a stroke is to exclude intracranial hemorrhage (10–15% of strokes) or other lesions such as a tumor, abscess, or SDH, which could be the cause of the patient’s neurological deficit. CT has a limited ability to detect acute ischemic changes within 12–24 hours of onset, although subtle signs of early ischemia can be detected in a substantial proportion of patients, even within 3 hours of stroke onset. After 24 hours, CT is better able to detect an ischemic stroke because there is more pronounced cerebral edema.

With the advent of thrombolytic therapy for patients that present within 3 hours of stroke onset, CT plays two additional roles in emergency patient care. First, and foremost, CT detects hemorrhage, which is an absolute contraindication to thrombolytic therapy. Second, a large area of early ischemic change is considered by some clinicians to be a contraindication to the use of thrombolytic therapy because it is associated with an increased risk of hemorrhage. A third potential role of imaging would be to confirm the diagnosis of an acute ischemic stroke, although CT has a limited ability to do this.

CT Signs of Ischemic Stroke

There are three stages in the evolution of an ischemic stroke as depicted on CT.

Acute ischemic changes occur within 24 hours and may be visible within three hours of the onset of stroke. These early ischemic changes are due to cytotoxic edema that accumulates intracellularly. Subacute changes occur after 24 hours, peak in 3 to 5 days, and gradually subside over 1 to 4 weeks. They are ...

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