Purpose: To determine the probability that regions of decreased apparent diffusion coefficient (ADC) return to normal without persistent symptoms or T2 change and the settings in which these ADC reversals occur.
Materials and methods: Three hundred magnetic resonance (MR) imaging studies were selected at random from a database of 7,147 examinations to determine the probability of a pathologically decreased ADC. In cases with decreased ADC, the clinical history was recorded and, if available, follow-up MR imaging findings were evaluated. Five cases of ADC reversal became known during 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 decreased ADC. In 49 of 116 studies, follow-up MR imaging examinations were performed at least 4 weeks after the onset of symptoms; ADC did not reverse. Five cases of ADC reversal were identified in the same period, giving an estimated 0.2%-0.4% probability of ADC reversal. Clinical settings were venous sinus thrombosis and seizure (n = 3), hemiplegic migraine (n = 1), and hyperacute arterial infarction (n = 1). Both white matter (n = 3) and gray matter (n = 3) regions were involved.
Conclusion: Reversal of ADC lesions is rare, occurs in complicated clinical settings, and can involve white or gray matter.