Snowball sign (Susac syndrome)

Last revised by Frank Gaillard on 28 May 2023

The snowball sign refers to the appearance of the corpus callosum on FLAIR and T2 weighted sequences in patients with Susac syndrome.

Within the substance of the body and splenium of the corpus callosum, best seen on sagittal images, are spherical well-demarcated high-signal regions 1,2.

This appearance is useful in distinguishing Susac syndrome from corpus callosal involvement in multiple sclerosis, where the lesions tend to preferentially involve the callososeptal interface and extend up into the callosal substance (this is the midline equivalent of Dawson's fingers).

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