Fig. 5.

Imaging findings in MELAS differential diagnoses. Exemplary FLAIR, DWI and ADC images of diseases that can mimic MELAS lesions on MRI including herpes simplex encephalitis, posterior reversible encephalopathy syndrome (PRES), subacute territorial ischemic stroke and recanalized territorial ischemic stroke are displayed. Herpes simplex encephalitis may mimic many MELAS MRI findings including cortical restricted diffusion (arrow), subcortical vasogenic oedema and local mass effect on FLAIR images. Nevertheless, herpes simplex encephalitis lesions usually affect mesiotemporal areas and spread continuously. PRES lesions are typically located in the occipital and temporal lobes showing subcortical vasogenic oedema (circle). Subacute ischemic stroke is hyperintense on FLAIR and diffusion is restricted, but the lesion is confined within a vascular territory. In case of early recanalization, restriction of diffusion may be limited to cortical areas but is usually more pronounced than in MELAS