Answer: D. Acute Infarct. This is an acute embolic non-hemorrhagic right middle cerebral artery infarct visible on CT. There is a hyperdense right middle cerebral artery with subtle loss of grey white differentiation consistent with an acute embolic infarct.
Figure (a) axial non contrast CT demonstrates a hyperdense middle cerebral artery. There is subtle loss of grey white differentiation involving the insular cortex (b) increased and decreased signal intensity respectively in the insula on diffusion weighted imaging (DWI) with apparent diffusion coefficient (ADC) consistent with an acute MCA territory infarct.
Discussion of CT signs of acute ischemic stroke
The recent use of intravenous tissue plasminogen activator (TPA) to treat acute stoke has resulted in the introduction of “code strokes” in many emergency rooms, which typically require the coordinated efforts of the emergency room physician, the neurologist and the neuroradiologist. Since TPA can only be administered within a narrow window (around three hours) after the onset of symptoms, rapid evaluation is essential – hence the saying “time is brain.”
CT is the initial imaging modality performed in the code stroke protocol. It is done primarily to exclude a hemorrhagic infarct, an absolute contraindication to the administration of TPA. However CT can also suggest the presence of a non hemorrhagic infarct with a sensitivity of approximately 70% – blurring of the junction between grey and white matter, especially in the insula is an early and often subtle sign of a non hemorrhagic infarct. A hyperdense MCA reflecting the increased attenuation of an clot within the vessel , is a specific sign for an embolic infarct.
MRI is the gold standard for the diagnosis of stroke but is not typically performed during a stroke code because of time constraints – a CT that shows no hemorrhage and high clinical suspicion for stroke is enough to justify treatment. Of the MRI sequences, diffusion weighted imaging is by far the most sensitive.
Recognizing the CT signs of acute non-hemorrhagic infarct is important in other situations as well. Patients who are poor historians, who have non-specific clinical exams and “altered mental status” can all have stroke and CT is often the first imaging modality performed in these patients.