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Diffusion-Weighted Magnetic Resonance Imaging in Radiation-Induced Cerebral Necrosis: Apparent Diffusion Coefficient in Lesion Components

Objective The objective of this retrospective study was to investigate the diffusivity of different components of radiation-induced cerebral necrosis with the hypothesis that the diffusivity of the various components is elevated to different degrees. Methods Twenty-two patients (18 men, 4 women, aged 34–72 years) with radiation injury to the temporal lobes after radiation therapy (RT) for nasopharyngeal carcinoma with diagnosis confirmed on serial magnetic resonance imaging (MRI) were studied with coronal T2-weighted, diffusion-weighted, and gadolinium-enhanced MRI. Using three diffusion directions for diffusion-weighted MRI, the apparent diffusion coefficients (ADCs) of the enhanced component, the cystic or liquefied component, and the edema component were measured. Results ADCs of all components of RT-induced cerebral necrosis (154 ± 21.6 × 10−5 mm2/s for contrast-enhanced component; 188 ± 47.4 × 10−5 mm2/s for cystic/liquefied component; 177 ± 35.4 × 10−5 mm2/s for edema component) were all significantly higher (P < 0.00001) than ADC of the normal frontal lobe white matter (82 ± 12.4 × 10−5 mm2/s). The ADC of the enhanced component was significantly lower than that of the cystic/liquefied component (P = 0.0096) and the edema component (P = 0.003). A significantly lower ADC was shown in the enhanced component in temporal lobes showing both short-term morphologic deterioration (P = 0.024) and occurrence of deterioration on long-term follow-up (P = 0.04) compared with the temporal lobes that showed improvement or stable morphology. Conclusions ADCs of the contrast-enhanced component, cystic/liquefied component, and edema in RT-induced cerebral necrosis was significantly higher than in normal brain parenchyma. There is association between a lower ADC in the contrast-enhanced component and morphologic deterioration.