Acute necrotizing encephalopathy associated with novel influenza H1N1 (pdm09) infection: MRI and correlation with brain necropsy

Abstract

In the United Kingdom, 2010 saw the second anticipated rise in the number of cases of novel influenza A H1N1 pdm09 (“swine flu”). Fatal outcomes largely relate to pulmonary sequel with fatal frank intracranial complications occurring much less frequently. Acute necrotizing encephalopathy is one such complication with a variable, but sometimes fatal, outcome. The condition has been reported largely in the East Asian pediatric population and is a very infrequent and elusive diagnosis largely because of the lack of recognition of the radiological appearances. The present case was diagnosed as a result of correlation of peri-mortem magnetic resonance imaging appearances of the brain with neuropathological findings at formal autopsy and brain necropsy: the virus was detected through reverse transcriptase polymerase chain reaction analysis and necropsy demonstrated classical features of necrosis in affected brain parenchyma with notable absence of inflammatory infiltrate. The report seeks to highlight the salient radiological feature of symmetrical hemorrhagic bilateral thalamic lesions - the presence of this particular feature in the appropriate clinical setting should prompt consideration of this radiologically elusive diagnosis.