目的：总结非典型脑膜瘤MRI表现特征。材料与方法：搜集11例经病理证实的非典型脑膜瘤，所有病例均行常规MRI平扫及增强检查，其中4例行扩散加权成像（DWI）。对肿瘤部位、大小、形态与边缘、增强前后信号特点、肿瘤周围水肿、硬膜尾征以及肿瘤内血管流空表现和DWI信号进行分析。结果：病变多见于大脑凸面，平均径线多>5cm，形态多不规则，部分瘤脑界面不清，信号不均匀，增强后多呈明显不均匀强化，肿瘤内多见流空血管影，病变于DWI上多呈高及稍高信号。病变周围水肿及硬膜尾征并无特异性。其中2例病变分别出现上矢状窦和邻近硬膜、颅骨及头皮软组织侵犯。结论：当发生在常见部位脑膜瘤体积较大，并同时表现出包括形态不规则、瘤脑界面不清、增强前后信号不均等多种不典型征象和/或肿瘤内多发流空血管、侵犯周围结构时应考虑非典型脑膜瘤的可能。

Objective: To summarize the MR imaging features of atypical meningiomas. Materials and Methods: There were 11 cases with atypical meningiomas proved by pathology, both plain and post-contrast MRI were performed in all the cases. Four cases had diffusion weighted imaging(DWI). The MRI manifestations including location, size, shape and margin of tumors, the signal intensity of lesions, the peritumor edema, dural tail sign, blood vessel flow void sign and signal intensity of DWI were analyzed. Results: Most of the lesions located in the cerebral convexity with average diameter larger than 5cm, and showed inhomogeneous signal intensity before and after contrast administration with irregular shape and blurred margin. In the lesion there were multiple flow void blood vessels and on DWI the tumor showed high and slightly high signal intensity. Two cases had invasion of sinus sagittalis superior, adjacent skull and soft tissue respectively. Peritumor edema and dural tail sign are not specific signs in the diagnosis of atypical meningiomas. Conclusion: When a tumor located in the common sites of meningioma with a larger size and atypical features including irregular shape, blurred margin between cerebral parenchyma and tumor, inhomogeneous signal intensity before and after contrast administration, blood vessel flow void sign in tumor and/or invasion of adjacent tissue, the diagnosis of atypical meningiomas should be considered.