Transient Splenial Lesion of the Corpus Callosum in Clinically Mild Influenza-Associated Encephalitis/Encephalopathy

BACKGROUND: Reversible lesions in the splenium of the corpus callosum (SCC), caused by various agents such as influenza, rotavirus, Escherichia coli , mumps, and adenovirus, were previously defined in a handful of cases. We present 5 cases with transient diffusion restriction of the SCC associated with influenza A virus infection. MATERIALS AND METHODS: Five patients with influenza-associated encephalitis/encephalopathy and sudden-onset neurologic symptoms following a prodromal flulike episode were examined by MR and diffusion-weighted imaging (DWI). RESULTS: Three patients, who had drowsiness and new-onset convulsions, recovered spontaneously without any medication. In the other 2 seizure-free patients, 1 had trigeminal neuralgia and headache and the other had facial numbness and left upper monoparesis. All patients had round well-defined ovoid hyperintense splenial lesions (14.94 ± 1.87 mm) on DWI with a significantly low apparent diffusion coefficient (ADC) of 0.41 ± 0.05 × 10 −3 mm 2 /s compared with 0.84 ± 0.01 × 10 −3 mm 2 /s of normal-appearing white matter. In the patient with a motor deficit, additional lesions were found in the cerebral deep white matter. The high signal intensity of the splenial and deep white matter lesions on DWI completely disappeared on follow-up studies, and ADC values also improved, returning to those of normal-appearing white matter on days 8–11. Clinically, all patients completely recovered on days 4–9. CONCLUSION: A transient lesion of the SCC is a significant but nonspecific finding. It is probably due to edematous and/or inflammatory changes of the SCC. It may be the only detectable change in patients with good prognosis, indicating a clinically mild form of encephalitis/encephalopathy.