Atypical MRI presentation of posterior reversible encephalopathy syndrome with predominant brainstem involvement.

We report here the case of a 80-year-old woman for the assessment of an acute confusional state since 2 days asssociated with diffuse and gradual headache. Brain MRI disclosed isolated hyperintense signal on fluid-attenuated inversion recovery sequence involving the medulla and the right inferior cerebellar peduncle with moderate swelling, consistent with vasogenic oedema, without abnormalities on diffusion-weighted imaging sequence. PRES diagnosis was suspected and antihypertensive therapy was introduced to achieve a blood pressure goal < 140/90 mmHg, allowing a quickly favourable clinical course. Three months later, brain MRI demonstrated a complete clearance of the abnormalities, confirming the PRES diagnosis. Atypical MRI findings are possible with involvement of basal ganglia, brainstem or cerebellum, but in these cases, oedema is most of the time accompanied by the classical parieto-occipital region involvement. Vasogenic oedema strictly unilateral or involving exclusively the brainstem or the cerebellum are very rare and should prompt suspicion for an alternative diagnosis. That constitutes a crucial diagnosis challenge in neurology.