Diffusion-weighted imaging characteristics of biopsy-proven demyelinating brain lesions

Objectives: To describe lesional diffusion-weighted imaging characteristics in a cohort of patients with biopsy-proven CNS inflammatory demyelinating disease (IDD) and compare diffusion characteristics of ring-enhancing CNS IDD lesions vs abscesses and tumors. Methods: Forty prebiopsy apparent diffusion coefficient (ADC) maps were reviewed from 30 patients with CNS IDD. Lesions were analyzed for size, T2-weighted (T2W) hypointense rim, enhancement, and ADC pattern. ADC patterns of CNS IDD ring-enhancing lesions were compared with a published cohort of 35 patients with ring-enhancing tumors and abscesses. Results: IDD lesions displayed a spectrum of peripheral ADC patterns at the lesion edge: restricted diffusion (low ADC), 33%; increased diffusion (high ADC), 60%; and normal diffusion (homogeneously isointense), 7%. Of biopsied lesions, 93% enhanced (ring, 52%; heterogeneous, 34%; homogeneous, 7%). A hypointense T2W rim was observed in 53%. A ring pattern on ADC (isointense or dark) was associated with T2W hypointense rims ( p = 0.02) but not with ring enhancement. On serial imaging, 4 of 7 (57%) patients demonstrated changes in ADC patterns. Peripheral restriction was more common in IDD ( p = 0.006) than in tumors or abscesses, whereas central restriction was only observed in abscesses. Restricted lesions in the same stage were more common in the non-IDD cohort (42% vs 20%), with a uniform restricted pattern seen only in abscesses. Conclusions: In ring-enhancing lesions, peripheral diffusion restriction is more common in IDD than in tumors/abscesses, whereas central restriction is more common among abscesses. Rapid ADC pattern changes in IDD probably reflect dynamic lesion evolution and may distinguish IDD from tumors.