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A 70-year-old man was brought to the Emergency Department after being found down at his home with an unclear time of symptom onset. He presented at 04:00h with a NIH Stroke Scale Score of 22, and was sent for a CT Angiogram and CT perfusion.

The RAPID mismatch map is shown above.

A large region of delayed contrast arrival is noted on the Tmax>6s map in the right MCA territory. There is no tissue with a severe reduction in CBF.

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The image columns demonstrate mild to moderate reduction of CBF, primarily involving the deep white matter of the right hemisphere.

Tmax and MTT maps demonstrate a significant perfusion abnormality throughout the right MCA territory. The CT angiogram was initially read as negative for large vessel occlusion, so no intervention was pursued.

Upon re-evaluation of the CT angiogram at 09:00h, a right MCA occlusion was noted. The patient continued to have an NIH Stroke Scale Score of 22.

A repeat CT, CT angiogram and CT perfusion scan was obtained at 09:30h.

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The maps from the second CT perfusion done at 09:30h (seen above) were very similar to the maps obtained from the first scan performed at 04:00h. Despite persistent occlusion of the right MCA, there was still no region of severe reduction in CBF. No early signs of infarction were noted on the non-contrast CT.

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The patient was sent for immediate endovascular thrombectomy and complete reperfusion was obtained.

The patient improved dramatically following the procedure and went on to have a very favorable clinical outcome.

This case study demonstrates that despite an MCA occlusion, collateral blood flow can maintain stable and adequate cerebral blood flow for many hours in some patients.