Double Doughnut Sign in Dengue Encephalitis - A Unique MRI Finding

Dengue virus, an RNA virus of family Flaviviradae, is typically considered non-neurotropic. However, increasing number of cases with neurological manifestations of dengue virus are being reported from India with significant morbidity and mortality. Dengue encephalitis is a seasonal disease in tropical countries and its imaging features are not widely known. We wish to discuss the MR imaging findings in two patients with dengue encephalitis. Our cases with dengue encephalitis showed bilateral symmetrical FLAIR and T2 hyperintensities in thalami, pons, and cerebellum on MR imaging. Concentric differential signal intensity of lesions in thalami resulting in double doughnut sign is a unique feature observed in both our cases. MRI features of dengue encephalitis are fairly characteristic and contribute to the early diagnosis and prompt management of cases. It is therefore very important that radiologists and treating clinicians be aware of these findings suggesting the possibility of dengue infection as a cause of encephalitis.