|MRI illustrating pertinent findings during the attack of headache and right homonymous hemianopsia (A and B) and at 2-week follow-up (C and D)|
The baseline MRI is done at 1.5 T and the follow-up MRI at 3 T. (A) At 150 minutes after symptom onset, axial isotropic diffusion-weighted imaging (b = 1,000 s/mm2) (a) is normal without ischemic injury. The circle of Willis on the time-of-flight magnetic resonance angiogram (MRA) (b) 155 minutes after symptom onset is also normal with symmetric arterial calibers. Axial fluid-attenuated inversion recovery (FLAIR) sequence at 170 minutes (c) is also normal. At 205 minutes, the T1 postcontrast “equilibrium” sequence (d) shows pial vessels dilatation (arrow), overlying the left occipital area. (B) Perfusion images at 210 minutes after symptom onset show symmetric relative cerebral blood volume (rCBV) map (a) and relative cerebral blood flow (rCBF) map (b) through the occipital lobes. The mean transit time (MTT) map (c) and the maximal time to peak of the residue function (Tmax) map (d) show mild delay in contrast arrival time in the left occipital pole. Using the RAPID automated software, the post-processed thresholded and segmented Tmax map (e) highlights 9.5 mL of tissue in blue with Tmax >4 seconds, indicating mild tissue hypoperfusion (benign oligemia). Only scattered and patchy areas within the area of mild hypoperfusion have a Tmax ≥6 seconds (currently accepted threshold2,7 for significant tissue ischemia) on the Tmax map (d) and these represented less than 3 mL of volume per RAPID (e). This pattern of normal rCBV, rCBF, mildly prolonged MTT and Tmax indicates only mild hypoperfusion without risk of progressing to infarction.2,7 Similar perfusion changes were seen in 3 additional contiguous slices through the left occipital pole. (C) Follow-up MRI at day 12 shows a normal axial isotropic diffusion-weighted imaging (b = 1,000 s/mm2) (a), normal time-of-flight MRA (b), and normal axial FLAIR (c), without any resultant tissue injury. The improved conspicuity of arteries on this MRA is due to higher magnet strength (3T). The T1 postcontrast sequence (d) shows complete resolution of the prior pial vasodilation. (D) On perfusion imaging, the rCBV (a) and rCBF (b) maps continue to be normal. MTT (c), Tmax (d), and RAPID (e) maps show complete resolution of the left occipital hypoperfusion.