Relationship between the concentration of supplemental oxygen and signal intensity of CSF depicted by fluid-attenuated inversion recovery imaging

Abstract

Background and purpose: Prior reports have described increased signal intensity (SI) of CSF on fluid-attenuated inversion recovery (FLAIR) images of anesthetized patients receiving 100% O(2). This appearance can simulate that of diseases. We evaluated the relationship between the concentration of inhaled O(2) and the development of increased SI of CSF on FLAIR images.

Methods: FLAIR was performed in 25 healthy volunteers breathing room air and 100% O(2) through a face mask for 5, 10, and 15 minutes. MR imaging, including FLAIR imaging, was performed in 52 patients with no potential meningeal abnormalities under general anesthesia: 21 received an equal mixture of N(2)O and O(2), and 31 received 100% O(2). The SI of CSF in volunteers and patients was graded in several locations by using a three-point scale.

Results: SI of CSF significantly increased (P <.05) in various locations, in both volunteers and patients breathing 100% O(2), when compared with SI in the same volunteers breathing room air. Hyperintensity of CSF was not significantly different in volunteers receiving 100% O(2) through a face mask compared with anesthetized patients receiving 100% O(2) through a laryngeal airway or an endotracheal tube. No significant increase in SI occurred in patients receiving 50% O(2), when compared with the SI of volunteers breathing room air.

Conclusion: Supplemental oxygen at 100% is a main cause of artifactual CSF hyperintensity on FLAIR images, regardless of the anesthetic drug used. This artifact does not develop when 50% O(2) is administered.

Fig 1.

FLAIR images of a healthy volunteer breathing room air show the expected suppression of the SI of the CSF in the cerebral sulci, fissures, and most of the cisterns.

Fig 2.

FLAIR images of the same healthy volunteer as in Figure 1 breathing 100% O₂ show hyperintensity in the cerebral sulci, fissures, and cisterns. There is no hyperintensity in the third and lateral ventricles.

Fig 3.

78-year-old female patient evaluated for suspected normal pressure hydrocephalus. A and B, MRI FLAIR sequence (1.0 T, TR 11,000 ms, TE 140 ms, TI 2,600 ms) shows dilatation of the ventricles and Sylvian fissures. C and D, FLAIR after 100% O₂ for 5 minutes shows increased SI in the sulci and in the posterior aspects of both Sylvian fissures, allowing visualization of hypointense cysts (arrows) due to neurocysticerosis more anteriorly within the Sylvian fissures. Note that there is no increase in the SI of the CSF within the ventricles.

Fig 4.

51-year-old male patient with headache. A and B, FLAIR image shows a large cyst with a scolex in the right Sylvian fissure and a cyst in the suprasellar cistern on the right, which are consistent with neurocysticerosis. The presence of an additional cyst in the perimesencephalic cisterns could not be ruled out due to prominence of these cisterns. C and D, FLAIR after 100% O₂ shows increased SI in the sulci and basal cisterns, confirming the absence of cysts in the perimesencephalic cisterns. In addition, there was improvement in the visualization of the cyst in the right suprasellar cistern and its relationship to the M1 segment of the ipsilateral middle cerebral artery.