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An 80-year old man with a history of hypertension presented 9 hours after the witnessed onset of severe right-sided weakness and numbness with an NIH Stroke Scale Score of 10. The RAPID MR mismatch map (shown above) demonstrated a perfusion deficit (Tmax > 6s) of 58 ml in the territory of the superior division of the left middle cerebral artery (MCA). There was no appreciable diffusion lesion with the ADC < 620.

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The MRI demonstrated a small acute ischemic lesion just anterior to the left insula (white arrow). MR angiography demonstrated reduced flow in the left MCA territory and susceptibility weighted imaging suggested an acute thrombus in an M2 branch in the Sylvian fissure (red arrow).

The 4 threshold Tmax map shows no tissue with Tmax > 10 seconds.

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The patient was treated with a low dose intra-arterial tPA infusion into the superior division of the left MCA. Excellent reperfusion was obtained. The patient had good collaterals on the angiographic study, which were anticipated based on the favorable Tmax profile (no tissue with Tmax > 10 seconds) on RAPID MR.

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The patient had a full clinical recovery. Nine days later, an MR scan demonstrated complete reperfusion and only a tiny ischemic lesion anterior to the insula.

This case demonstrates that patients with good collaterals can have ischemic symptoms for many hours without developing a significant infarct. In addition, patients with M2 occlusions may have a large volume of tissue at risk.