Trident sign (persistent primitive trigeminal artery)

Last revised by Yaïr Glick on 4 Feb 2024

The trident sign of a persistent primitive trigeminal artery refers to the appearance of the intracranial circulation on lateral projection. The internal carotid artery, the abnormal vessel and superior portion of the basilar artery resemble the Greek letter tau (thus tau sign). This configuration is also referred to as the trident sign 1, although, as there are only two upwardly pointing branches (terminal ICA and basilar artery) this would probably be better termed a bident

History and etymology

The trident is a three-pronged lance employed for spearing fish, and in Classical mythology was the weapon borne by sea gods, such as the sea god Poseidon in Ancient Greece (or Neptune, the Roman equivalent). 

Poseidon's older brother, Hades/Pluto has a two-pronged staff, known as a bident, which is actually a better fit for the morphology of this abnormality 2

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