Double doughnut sign

Last revised by Rohit Sharma on 1 Nov 2024

The double doughnut sign is a radiological sign described in MRI of viral encephalitis, typically due to dengue encephalitis.

The double doughnut sign refers to a pattern of signal changes in the bilateral thalami that have a doughnut-like appearance 1-4. This sign may be appreciated on either T2/FLAIR, diffusion-weighted imaging (DWI) or susceptibility weighted imaging (SWI), with bilateral round thalamic hyperintensities, each with a low signal core, that give the appearance of two (i.e. double) doughnuts 1-4. This appearance is thought to be due to bilateral thalamic hemorrhages occurring within surrounding edema and diffusion restriction 1-4.

This sign has been typically described, albeit rarely, in dengue encephalitis 1-4. However, there are case reports of its description in other flavivirus encephalitides (e.g. Japanese encephalitis) 1-4.

Differential diagnosis

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