Associate Professor of Radiology Tehran University of Medical Science, Tehran, Iran
Mimics account for almost half of hospital admissions for suspected stroke. While many underlying conditions can be recognized rapidly bycareful assessment,asignificantproportion of patients still receive thrombolysis and admission to ICU with unnecessary costs. Accurate diagnosis is important and MRI is necessary if stroke mimics are suspected. Stroke mimics can broadly be classified into two categories, Medical mimics 50–80% of cases and Functional mimics. Conditions that mimic stroke include metabolic disorders such as hypoglycemia, hyperglycemia, hypernatremia, hyponatremia, uremia, metabolic encephalopathy, and hyperthyroidism. Moreover, migraine, seizure, psychological disorders, demyelinating diseases, intoxication and brain tumors may also mimic stroke. MRI is the best technique to identify stroke mimics. Diagnostic evaluation can be approached based on diffusion- weighted imaging (DWI), which can be abnormal or normal, followed by the results of other MRI sequences, such as T2-GRE and fluid- attenuated inversion recovery (FLAIR). Analysis of the signal intensity of the parenchyma, the intracranial arteries and, overall, of the veins, is crucial on T2-GRE, while anatomic distribution of the parenchymal lesions is essential on FLAIR. Among stroke mimics with abnormal DWI, T2- GRE demonstrates obvious abnormalities in case of intracerebral haemorrhage or cerebral amyloid angiopathy. FLAIR is very useful when DWI is positive by showing distribution of cerebral lesions in case of seizure (involving the hippocampus, pulvinar and cortex), in posterior reversible encephalopathy syndrome (PRES) or hypoglycaemia (bilateral lesions in the posterior limb of the internal capsules, corona radiata, striata splenium of the corpus callosum). Other real stroke mimics such as MELAS, brain tumour, demyelinating diseases and encephalitis can be diagnosed by MRI. Neurotoxicity should also be considered in patients with underlying diseases treating by chemotherapy presenting with acute neurologic symptoms.