Significance of hyperintense vessels on FLAIR MRI in acute stroke

To the Editor:

We read with interest the article by Kamran et al.1 describing the hyperintense vessel sign (HVS) on the fluid attenuated inversion recovery (FLAIR) sequence in patients with acute middle cerebral artery stroke. HVS was associated with large vessel occlusion or severe stenosis, which were proved by other imaging modalities. We agree that this MR finding is a useful sign for both diagnosis and management.

The authors suggested that sluggish blood flow near ischemic or infarcted tissue results in the loss of flow voids, and vessels appear hyperintense against a dark CSF background. In normal cerebral circulation, flowing blood is demonstrated as loss of signal in the blood vessels (flow void) because of high velocity, turbulence, and dephasing. It is important to remember that flow void is most evidently demonstrated on proton-density–weighted MRI (PDWI: long repetition time [TR]/short echo time [TE] images). We present a case of a 70-year-old man with right middle cerebral artery occlusion (figure). MR examination was performed 6 hours after onset on a 1.0-T scanner. HVS was noted in right sylvian fissure on FLAIR images (TR = 6500, TE = 110, delay time [TI] = 1700 ms; figure, A and B), and the flow voids of the corresponding arterial branches were absent on PDWI obtained using fast spin-echo technique (TR = 2500, TE = 22 ms; figure, C and D). Postcontrast T1-weighted images (T1WI) showed intravascular enhancement (not shown).

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Figure. MR images taken 6 hours after onset of right middle cerebral artery occlusion in a 70-year-old man.

The usefulness of PDWI in patients with cerebral artery disease has been reported.2-4⇓⇓ The same mechanism is responsible for HVS on FLAIR and the loss of flow void on PDWI. Because PDWI has better signal-to-noise ratio, we suppose that PDWI can equally or more reliably demonstrate vessel occlusion. Another advantage of PDWI over other MR sequences is that PDWI can be obtained by the same sequence of T2-weighted images, so no additional scanning or contrast material is necessary. Although a direct comparison between FLAIR and PDWI is required, we suspect that absence of flow voids on PDWI may help prompt diagnosis as well as HVS on FLAIR.