[Flair and diffusion weighted MR imaging in differentiating epidermoid cysts from arachnoid cysts]

To explore the use of fluid-attenuated inversion recovery (FLAIR) and diffusion-weighted echo planar imaging sequences in imaging of the intracranial epidermoid and arachnoid cysts and assess the efficiency of those sequences in differentiation of epidermoid cysts from arachnoid cysts.

This study was performed prospectively by using two different MR devices in 24 patients (12 epidermoid cysts, 12 arachnoid cysts). T1-weighted spin echo, T2-weighted fast spin echo, FLAIR and diffusion-weighted echo planar imaging sequences were used. Lesions were evaluated qualitatively and quantitatively. In qualitative evaluation, the signal intensity of the lesions were compared with cerebral spinal flow. Quantitative evaluation was made from the diffusion-weighted images by measuring values of apparent diffusion coefficient (ADC) from the cystic spaces and cerebral white matters. In statistic analyses, Mann-Whitney U test was used.

Arachnoid cysts had the same intensity with cerebral spinal flow in all sequences. Mean ADC value was 3.41 +/- 0.17 x 10(-3) mm2/sn. All epidermoid cysts on diffusion-weighted trace images were more hyperintense than brain parenchyma. The mean ADC value of the epidermoid cysts was 1.15 +/- 10(-3) mm2/sn. The ADC values of the epidermoid cysts were lower than the arachnoid cysts (p < 0.001), but were higher than the cerebral white matter (p < 0.01).

FLAIR sequences were superior to conventional sequences in imaging of epidermoid cysts and in differentiation of epidermoid cysts from arachnoid cysts. It was also shown that diffusion-weighted trace imaging and measurement of ADC values might be used as problem solving tools. Furthermore, those sequences may be a guide to demonstrate postoperative residual lesions.