Frequency and clinical context of decreased apparent diffusion coefficientreversal in the human brain

PURPOSE: To determine the probability that regions of decreased apparent di ffusion coefficient (ADC) return to normal without persistent symptoms or T 2 change and the settings in which these ADC reversals occur. MATERIALS AND METHODS: Three hundred magnetic resonance (MR) imaging studie s were selected at random from a database of 7,147 examinations to determin e the probability of a pathologically decreased ADC. In cases with decrease d ADC, the clinical history was recorded and, if available, follow-up MR im aging findings were evaluated. Five cases of ADC reversal became known duri ng the same period and were evaluated to determine the initial ADC decrease , clinical outcome, and findings at follow-up imaging. RESULTS: Findings in 116 of 300 MR imaging studies revealed regions of decr eased ADC. In 49 of 116 studies, follow-up MR imaging examinations were per formed at least 4 weeks after the onset of symptoms; ADC did not reverse. F ive cases of ADC reversal were identified in the same period, giving an est imated 0.2%-0.4% probability of ADC reversal. Clinical settings were venous sinus thrombosis and seizure (n = 3), hemiplegic migraine (n = 1), and hyp eracute arterial infarction (n = 1). Both white matter (n = 3) and gray mat ter (n = 3) regions were involved. CONCLUSION: Reversal of ADC lesions is rare, occurs in complicated clinical settings, and can involve white or gray matter.