Introduction: MR imaging criteria for diagnosing acute disseminated encephalomyelitis (ADEM) have not been clearly established. Due to the wide spectrum of differential considerations, new imaging features allowing early and accurate diagnosis for ADEM are needed. We hypothesized that ADEM lesions would be characterized by vasogenic edema due to the potential reversibility of the disease.
Methods: Sixteen patients who met the diagnostic criteria for ADEM proposed by the International Pediatric Multiple Sclerosis Study Group (IPMSSG) and had complete MR imaging studies performed at our institution during the acute phase of the disease were identified retrospectively and evaluated by experienced pediatric neuroradiologists.
Results: Vasogenic edema was demonstrated on diffusion-weighted imaging (DWI) and corresponding apparent diffusion coefficient (ADC) maps in 12 out of 16 patients; cytotoxic edema was identified in two patients while the other two patients displayed no changes on DWI/ADC. ADC values for lesions and normal-appearing brain tissue were 1.39 ± 0.45 × 10(-3) and 0.81 ± 0.09 × 10(-3) mm/s(2), respectively (p=0.002). When considering a cutoff of 5 days between acute and subacute disease, no difference between ADC values in acute vs. subacute phase was depicted. However, we found a significant correlation and an inverse and significant relationship between time and ADC value.
Conclusion: We propose that vasogenic edema is a reliable diagnostic sign of acute neuroinflammation in ADEM.