Effects of Oxygen on FLAIR

A 30 yo pt brought unconscious, required intubation and O2 support. MRI axial FLAIR brain screening show diffusely increased signal in the subarachnoid spaces in the region of cortical sulci and basal cisterns but Csf examination was normal.

An Artifactual high signal in Csf spaces due to para magnetic effect of inhaled Oxygen.
"Pseudo SAH" 

Patients who are intubated and on inhaled oxygen, once the concentration of dissolved oxygen is high enough in the blood, its level will increase in the CSF as well leading to sub optimal suppression of Csf signal on FLAIR due to para magnetic effect of Oxygen and results in diffuse Csf T2 hyper intensity.

Reference: Practical MR Physics and case file of MR artifacts and pitfalls, Alexander C. Mamourian, MD

IVY sign in major vessel stenosis

A  7yo patient came for MRI Brain with history ... no need to mention here as it was not specific and i am sure it was not related to patient's imaging findings. 

Only Axial FLAIR images of patient were abnormal with a subtle finding. Rest of the MRI study including Diffusion and GRE were absolutely normal.

Guess !! the finding.

Faint serpigenous high signal in right peri sylvian cortical sulci are the cortical branches of right MCA with sluggish flow attributed to IVY sign.

and that's his angio... 

Click image to enlarge. 

3 D TOF Non contrast MR Angiography of brain shows severe right MCA proximal main stem stenosis with sparsity of cortical branches of right MCA compared to left. 

'IVY' sign

Normally cortical branches of major intra cranial vessels which travel along hemispheric cortical sulci are not visualised on FLAIR.

Due to any reason if the flow in these cortical branches hampered, the slow flow in these cortical branches or the cortical collaterals developed thereby , reflect high signal on FLAIR, relatively higher than that of adjacent normal isointense brain parenchyma and seen as serpigenous hyperintensities in the region of cortical sulci on FLAIR attributed to IVY sign. 

IVY sign is reported in following conditions.

Moya Moya disease or major intra cranial vessel stenosis lead to cortical branches with slow flow or development of collaterals with sluggish flow.

Early ischemia thrombus in cortical branches may reflect high signal on FLAIR

Vasculopathies. 

To see similar cases with other causes of IVY sign : Click here