Hyperintense Subarachnoid Space on FLAIR

Increased FLAIR signal may be seen in the subarachnoid space in conditions other than subarachnoid hemorrhage. Differential diagnosis:

• Acute subarachnoid hemorrhage
• Meningitis
• Susceptibility artifact
• High levels of inspired oxygen (e.g., in sedated kids)
• Meningeal metastases
• Leaky blood-brain barrier from cerebritis, PRES
• Delayed gadolinium clearance in renal failure
• Acute infarction (thought to be related to slow flow)
• Ruptured dermoid Cyst
• Moyamoya