According to many studies, in cases of stroke, FLAIR signal intensity changes are variable and mostly detected within 6–12 h after onset of symptoms. In management plan of stroke cases, presence of restricted diffusion and negative FLAIR findings has been adequate to begin therapy [6, 7]. Many recent studies reported that positive diffusion restriction while negative FLAIR sequence study indicates that the stroke is less than 6 h old [3, 8]. Thomalla et al.  reported that (in 120 consecutive patients with stroke) positive findings in DWI and negative FLAIR findings were highly suggestive that the stroke was less than 3 h old. Similar results were reported by Aoki et al.  (of 333 consecutive patients with stroke). However, it is important to know how much signal intensity can vary at FLAIR imaging as there was reported one patient with no positive FLAIR findings until 24 h after positive changes detected in DWI and ADC map .
On the other hand, many patients with acute stroke show false-negative findings at DWI, while showing positive findings in FLAIR .
In cases of acute stroke, bright signal intensity of the large and small vessels may be seen on FLAIR sequence as the only positive changes of the brain that indicate early ischemic infarction. This finding known as “FLAIR vascular hyperintensity (FVH)” also, known as hyperintense vessel sign or arterial hyperintensity . The pathophysiologic basis of this sign still unclear, however there are many theories like slowly or stagnant blood flow, intraluminal thrombus or embolus. Arterial hyperintensity may be detected at FLAIR imaging very early in acute stroke, within 0–2 h after onset of symptoms [13, 14].
The sensitivity of this sign is highest during the first 6 h after symptom onset then decreased by time. It is commonly seen at the Sylvain fissure, followed by the cortical sulci, the horizontal segments of the middle cerebral arteries in the affected middle cerebral artery distribution and rarely seen at the posterior cerebral arteries. FVH sign can be easily missed if the radiologist does not aware or actively looking for it [1, 3].
The presence of FVH in association with the positive restricted DWI is an indication of impending infarction and needs rapid management and flow augmentation strategies [6, 7]. Sometimes, FVH can precede diffusion abnormalities as in our case. One of the recent studies reported that the area of the FVH almost equal to that of a perfusion abnormality, particularly in patients examined within 6 h of symptom onset .
Other recent studies reported that the presence of FVHs beyond the boundaries of a restricted DWI area (FVH-DWI mismatch) is suggestive of a large penumbra in PWI and cope with (PWI-DWI mismatch) that indicate large infarct growth .
Another quantitative analyses study done by Nomura et al.  based in comparison of the hypoperfusion between the FVH low and FVH high groups. They reported that the large hypoperfusion area was detected in patients with FVH high group more than patients with FVH low group.