Discrimination between different types of white matter edema with diffusion‐weighted MR imaging

Abstract Brain edema can be classified into three categories: vasogenic, cytotoxic, and interstitial. The mechanism of edema is thought to be different in each type. The authors studied the movement of water molecules in each type of white matter edema in a rat model by using diffusion‐weighted magnetic resonance imaging. Conventional T2‐weighted imaging did not allow distinction between the three types of white matter edema; the three types of edema were, however, distinguished by using diffusion‐weighted imaging. The apparent diffusion coefficient (ADC) of water was different in each type of edema. Water molecules in cytotoxic edema induced by triethyl‐tin intoxication showed a smaller and less anisotropic ADC than in normal white matter. In contrast, water in vasogenic edema induced by cold injury had a larger and more anisotropic ADC than in normal white matter. Water in interstitial edema due to kaolin‐induced hydrocephalus had an anisotropic and very large ADC.