Trident sign (osmotic demyelination)

Last revised by Daniel J Bell on 12 Mar 2021

The trident sign (a.k.a. omega sign) describes the typical appearances of the pons in osmotic demyelination syndrome, whereby the symmetrical high T2/FLAIR signal abnormality centrally in the pons is shaped like a trident, the three-pronged spear of classical Greece 1. The predominant involvement of the transverse pontine fibers and relative sparing of the descending corticospinal tracts is responsible for this characteristic ‘trident’ or omega shaped appearance 2.

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 classical Roman equivalent). Although a similar weapon, the trishoola, with rounded tines, is also seen being carried in images of Hindu gods, e.g. Shiva and Durga 1,3.

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