Multimodal Quantitative Characterization of Intracranial Epidermoid Cysts: Preliminary Results

Background and purpose - The differentiation of epidermoid cysts from other intracranial lesions with CT and conventional MR imaging is challenging. The risk of residual and recurrent disease is high and multimodal imaging should therefore promote a precise differential diagnosis. Since epidermoid cysts are histologically identical to middle ear cholesteatomas, MRI methods that are useful in the diagnosis of cholesteatoma; specifically EPI DWI and a non- EPI diffusion subtype (HASTE DWI) may possibly be applicable to epidermoid cysts. Besides testing the diagnostic utility of these methods on epidermoid cysts, our goal was to quantify the T1 and T2 relaxation times, the ADC values and the magnetization transfer ratios in order to acquire objective, characteristic information about their structure and contents. Finally, our goal was to provide the physician with a reliable, multimodal diagnostic tool that supports accurate surgical planning. Methods - Two patients with epidermoid cysts were examined. Besides the conventional MR scans EPI DWI, HASTE DWI, quantitative T1, T2 and magnetization transfer measurements were performed mappingwith a 3T MR scanner. After image registration, T1, T2 relaxation times and the magnetization transfer ratio inside a ROI were determined according to the lesion location on HASTE DWI. Mean ADC values inside the epidermoid cysts were also calculated by both mono-exponential and bi-exponential diffusion models. Results - Our results revealed relatively high T1 and T2 relaxation times and ADC values, and low magnetization transfer ratios in both subjects. Conclusion - HASTE-DW MRI provides accurate morphologic information on epidermoid cysts, while T1, T2, ADC and magnetization transfer ratio maps are quantitative techniques. Thus the combination of these methods results in a confident preoperative diagnosis and aids to determine the indication of retreatment in the event of recurrence.