Acute encephalopathy occuring in infants and children often after outbreaks of the H1N1 variant of influenza A.
On imaging patients have bilateral thalamic lesions showing increased T2 signal, which are continuous with lesions in the lateral putamina and external/extreme capsules. Patients also show increased T2/FLAIR signal in the brain stem (tegmentum or whole brainstem) and in the nuclei and deep white matter of the cerebellum
Patients with mutations of the RANBP2 gene have been associated with familial and recurrent acute necrotizing encephalitis, and is known as acute infection-induced encephalopathy-3.