Tau sign

Last revised by Andrew Murphy on 30 Oct 2024

The tau sign represents the appearance of a persistent primitive trigeminal artery on the sagittal plane of an angiogram or on sagittal MRI images. It resembles the Greek letter τ, pronounced "tau", and is equivalent to the modern-day "T" in the Latin alphabet.

The persistent trigeminal artery arises from the junction between the petrous and cavernous ICA and runs posterolaterally along the trigeminal nerve through, or adjacent to, the cavernous sinus.

The vertical and anterior horizontal limbs of "Tau" are formed by the internal carotid artery (ICA) and the posterior horizontal limb is formed by the proximal portion of the persistent trigeminal artery.

Cases and figures

  • Case 1
  • Case 2
  • Case 3
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