Presentation
Non-specific headache
Patient Data
Note: This case has been tagged as "legacy" as it no longer meets image preparation and/or other case publication guidelines.
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Note a flow void connecting carotid and basilar systems on left side consistent with a persistent trigeminal artery. The "tau sign" is best seen on sagittal images.
Case Discussion
The tau sign refers to the unusual configuration of signal voids in the presellar ICA and in a persistent trigeminal artery, as viewed on parasagittal MR images.
The combination of the vertical and horizontal segments of the ICA and the proximal portion of the trigeminal artery creates the outline of the Greek letter "τ".