The posterior reversible encephalopathy syndrome (PRES) is a clinical and radiological entity defined by headache, altered mental status, seizures, visual abnormalities, and characteristic findings on neuroimaging.
The typical PRES pattern at CT/MR imaging demonstrates symmetrically distributed areas of vasogenic oedema predominantly within the posterior regions of the cerebral hemispheres. When promptly recognized and treated, the neurologic symptoms and radiologic abnormalities can be completely reversed. Because CT-scan can be normal in PRES, MRI is always the examination of choice. FLAIR (fluid-attenuated inversion-recovery) images allow identif ication of more subtle lesions and PRES could be diagnosed earlier. PRES lesions are associated with vasogenic oedema which is isointense or hypointense in DWI (diffusion-weighted imaging) images and hyperintense in ADC (apparent dif fusion coefficient) maps. This differentiates
PRES from early cerebral ischaemia and stroke when cytotoxic oedema, which has high signal intensity on DWI, due to decreased ADC, is present. In more severe cases of PRES changes in cerebrovascular autoregulation may lead to vasospasm, ischaemia and development of cytotoxic oedema. In the studied cases ischaemic injury and cytotoxic oedema were present but according to follow-up MRI these changes are reversible. DWI could be used to monitor for ischaemia as a complication of PRES.
PRES is an increasingly recognized complication of paediatric cancer treatment particularly in paediatric acute leukemia. The role of neuroimaging is to establish PRES diagnosis and to exclude other causes of neurological symptoms and signs.