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A 22-year-old man developed acute fever and malaise. On the third day of fever, he had a dull-aching bilateral headache and orbital pain, predominantly right-sided, and photophobia. He had been previously healthy and lived in Bangkok, Thailand. Neurological examination was normal, without meningeal irritation, cortical lobe signs or interhemispheric disconnection syndrome. MR scan of brain using diffusion-weighted imaging (DWI) and apparent diffusion coefficient (ADC) sequences showed a non-enhancing focal restricted diffusion lesion in the splenium part of the corpus callosum, representing a ‘dot sign’ ( figure 1 , Panels A-B). MR imaging using T2-weighted fluid attenuation inversion recovery (T2/FLAIR) sequences showed a mildly hyperintense lesion in the splenium (figure 1 , Panel C). Serum dengue NS1 antigen was positive, but dengue virus-specific IgM and IgG antibodies were negative. Serum multiplex PCR confirmed dengue virus infection. With supportive treatment, he recovered with no residual neurological deficits. Follow-up MR imaging showed complete resolution of the corpus callosal lesion (image not shown).