Tau sign

Last revised by Dr Daniel J Bell on 04 Sep 2019

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.

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Cases and figures

  • Figure 1: schematic: tau sign
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  • Case 1
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  • Case 2: pineal cyst and trigeminal artery
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