Imaging in influenza A encephalitis

Two cases of influenza A encephalitis seen during an outbreak of influenza types A/England/427/88 (H3N2) and A/Taiwan/1/86 (H1N1) in December 1989 are described. In both children the encephalitis developed within three days of the respiratory symptoms and both became comatose within 48 hours. Virological studies showed that the patients had had a recent influenza A infection. Symmetrical localised hypodense lesions within the thalami and pons were demonstrated in both cases on computed tomography of the brain and striking findings in the pons in one case on magnetic resonance imaging. Influenza A encephalitis is not easy to recognise clinically and serological confirmation can only be made after 10 days. Imaging may provide evidence in the acute stage to support a diagnosis of influenza encephalitis during influenza outbreaks.