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Ischemic Stroke

Radiographic Summary

Suspected ischemic stroke is one of the most common indications for neurological imaging in the ED. Initial imaging includes NECT and/or MRI. Stroke MRI protocols may be completed in 10 minutes if resources permit, including perfusion imaging. CT findings of acute stroke may include “hyperdense MCA sign” or “dot sign”, which is due to thrombus within the proximal MCA or Sylvian MCA branch, “insular ribbon sign” due to obscuration of the insular cortex due to edema, and parenchymal hypodensity. Most commonly however, NECT will be normal in the initial stages of ischemic stroke. Later findings include the development of hypodensity, gyral swelling and sulcal effacement. Hemorrhagic transformation is most common after 1-2 days.

Many centers include CTA or CT Perfusion (CTP) immediately following NECT. CTA allows assessment of stenoses, dissections, vasculitis, or intracranial large vessel thrombus. CTP assesses cerebral blood flow and identifies the core infarct and surrounding tissue-at-risk (penumbra).

DWI is the most sensitive MR sequence for acute ischemia. Findings of “restricted diffusion” are a bright signal on DWI with a corresponding dark signal on ADC. Findings become positive within minutes of ischemia and remain positive for 10 days. MRA can be obtained as an alternative to CTA.

MR perfusion-weighted imaging (PWI) can be obtained with contrast analogous to CTP. In combination with DWI, mismatches between DWI infarct and PWI ischemic tissue can be used to determine if any salvageable penumbra tissue exists.

Clinical Implications

An ischemic stroke results from brain hypoperfusion due to thrombus, emboli, dissection, stenosis, or hypotension. Patients with ischemic stroke may present with the sudden onset of focal neurologic deficits such as motor weakness, sensory deficits, or speech difficulties. Current NINDS guidelines recommend that the ED physician complete the initial assessment and NECT within 25 minutes of patient arrival to maximize potential benefit for reperfusion therapy.

Figure 2.1 ▪ Ischemic Stroke.

A: NECT shows subtle loss of the left insular ribbon (region between the lentiform nuclei and Sylvian fissure), sulcal effacement, and mild edema that blurs the gray-white interface. Findings suggest acute MCA infarction. B: NECT shows hyperdensity in the region of the left middle cerebral artery (“hyperdense MCA sign”) (arrow). C: Axial CTA confirms the thrombus occluding the proximal (M1) segment of the left MCA with little collateral flow distally (arrow). D: Conventional angiogram of left carotid injection shows cut-off of middle cerebral artery on left corresponding to the CTA (arrow). Normal ...

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