There are no formal diagnostic criteria for<unk> , but it has been proposed that<unk>  can be diagnosed if someone has developed acute neurological symptoms (seizure, altered mental state, headache, visual disturbances) together with one or more known risk factors, typical appearance on brain imaging (or normal imaging), and no other alternative diagnosis. Some consider that the abnormalities need to be shown to be<unk> . If lumbar puncture is performed this may show increased protein levels but no white blood cells. Computed tomography scanning may be performed in the first instance; this may show low density white matter areas in the<unk>  lobes. The diagnosis is typically made with magnetic resonance imaging of the brain. The findings most characteristic for<unk>  are symmetrical hyperintensities on T2-weighed imaging in the parietal and occipital lobes; this pattern is<unk> ent in more than half of all cases. FLAIR sequences can be better at showing these abnormalities. Some specific other rare patterns have been described: the superior frontal sulcus (SFS) watershed pattern, a watershed pattern involving the entire hemisphere (holohemispheric), and a central pattern with vasogenic oedema in the deep white matter, basal ganglia, thalami, brainstem and pons. These distinct patterns do not generally correlate with the nature of the symptoms or their severity, although severe edema may suggest a poorer prognosis. If the appearances are not typical, other causes for the symptoms and the imaging abnormalities need to considered before<unk>  can be diagnosed conclusively. In many cases there is evidence of constriction of the blood vessels (if angiography is performed), suggesting a possible overlap with<unk>  cerebral vasoconstriction<unk>  (RCVS). Diffusion MRI may be used to identify areas of cytotoxic edema caused by poor blood flow (ischemia) but it is not clear if this prognostically relevant. Abnormal apparent diffusion coefficient is seen in about 20% of cases. In 10–25% of cases of<unk>  there is evidence of hemorrhage on neuroimaging. Various types of hemorrhage may occur: hemorrhage into the brain tissue itself (intraparenchymal hemorrhage), sulcal subarachnoid hemorrhage, and microbleeds.
Posterior reversible encephalopathy syndrome
Viral encephalitis
Autoimmune encephalitis
Lymphocytic meningoradiculitis
Limbic encephalitis
Wernicke encephalopathy
Chronic traumatic encephalopathy
Hypertensive leukoencephalopathy