扩散加权成像最小ADC值对四脑室常见原发肿瘤的鉴别诊断价值

The Minimum DWI ADC Value in Differentiating Common Primary Tumors of Fourth Ventricle

目的总结归纳四脑室常见原发性肿瘤常规MRI表现及扩散加权成像(DWI)最小表观扩散系数(ADC)值的特点和差异,探讨其鉴别诊断价值。方法回顾性分析经病理证实的80例四脑室常见原发肿瘤的一般临床资料及MRI特点,测量肿瘤实质平均最小ADC值,并进行统计学分析。结果髓母细胞瘤(36例)较典型的MRI表现是小脑扁桃体下疝或小脑半球明显受压后移,肿瘤在DWI上呈扩散受限高信号,瘤体最小ADC值为(0.47±0.13)×10-3mm2/s;星形细胞瘤(25例)占位效应较显著,最小ADC值为(1.62±0.55)×10-3mm2/s;室管膜瘤(19例)典型的MRI表现是"溶蜡"样变,瘤体最小ADC值为(0.90±0.21)×10-3mm2/s。对髓母细胞瘤、星形细胞瘤及室管膜瘤3种肿瘤的平均最小ADC值进行方差分析,再两两比较行LSD-t检验,其差异有统计学意义(P<0.01)。DWI受限高信号且以平均最小ADC值0.870×10-3mm2/s为阈值,与病理结果对照,诊断四脑室髓母细胞瘤的敏感度为96.7%,特异度98.4%,阳性预测值100%,阴性预测值98.2%,与组织学结果行一致性检验,Kappa值为0.903。结论常规MRI联合DWI及ADC值测定,对于鉴别诊断四脑室常见原发肿瘤性质具有明确的应用价值。

Objective To summarize the MRI features of common primary tumors locating in the fourth ventricle,and to investigate the minimum DWI ADC value in differentiating common primary tumors of the fourth ventricle. Methods A total of 80 patients with pathologically-proved common tumors of the fourth ventricle were enrolled in this study. The clinical data and MRI findings were retrospectively analyzed. The mean minimum apparent diffusion coefficients（ ADC） values of tumors were calculated,and the results were statistically analyzed. Results The lesions included medulloblastoma（ n= 36）,astrocytoma（ n = 25） and ependymoma（ n = 19）. On MRI,the medulloblastoma was characterized by tonsil hernia or significant compression and o backward displacement of the cerebellum. The tumor presented as diffusion-limited on DWI with a minimum ADC value of（ 0. 47 ± 0. 13） × 10- 3mm2/ s. The astrocytoma had obvious space-occupying effect,the minimum ADC value was（ 1. 62 ± 0. 55） × 10- 3mm2/ s. The ependymoma was typically manifested as ＂melted wax＂appearance on MRI,and the minimum ADC value was（ 0. 90 ± 0. 21） × 10- 3mm2/ s. Variance analysis and LSD test indicated that statistically significant difference in the minimum ADC value existed between each other among the three tumors（ P 〈0. 01）. Taking the minimum ADC of 0. 870 × 10- 3mm2/ s as the threshold and compared with the pathological results,the diagnostic sensitivity,specificity,positive predictive value and negative predictive value of diffusion-weighted limited high signal were 96. 7%,98. 4%,100% and 98. 2% respectively for medulloblastomas of the fourth ventricle,and the consistency checking with histological results showed that Kappa value was 0. 903. Conclusion Conventional MRI combined with DWI and ADC value estimation has definite and practical application value in differentiating common primary tumors of the fourth ventricle.