胡步宏 賈中正 耿道穎

低級別膠質瘤(low-grade glioma,LGG)與反應性膠質增生(reactive gliosis,RG)影像特征相似,在常規(guī)CT/MRI上很難鑒別,而兩者的治療方案明顯不同。LGG容易惡變成間變性膠質瘤,甚至是膠質母細胞瘤。一旦診斷為LGG,必須盡早手術切除。RG是膠質細胞在數(shù)量上的增加,很少惡變(即使惡變成膠質瘤,也需要很長時間),所以RG只需要隨訪,不需要手術。因此,LGG與RG的準確鑒別對于患者的治療計劃與預后評估異常重要。近年來有關膠質瘤表觀彌散系數(shù)(ADC)值的研究報道越來越多。因此,我們設想ADC值在鑒別LGG與RG方面可能存在價值。本研究目的是探討最小相對ADC(rADCmin)值在LGG與RG鑒別診斷中的價值。

方 法

1.臨床資料

收集經(jīng)病理證實的58例LGG(WHO Ⅱ級)和11例RG患者,其中男40例,女29例,年齡10～69歲,平均36.2歲。在MRI檢查前所有患者未進行過干預治療,每例患者均在MRI檢查后一周內手術。

2.MRI成像與后處理

所有MRI檢查均在GE3.0 M R掃描儀 (Signa VH/I,GE Healthcare,Milwaukee)上進行,掃描使用8通道頭頸線圈。常規(guī)MRI包括FLAIR(TR/T E/T I 8502ms/124ms/2250ms,層厚 5mm,間隔 2mm,矩陣288×224,FOV24.0×24.0cm,2次采集);T1-FLAIR(T R/TE/T I2205ms/18.3ms/860ms,層厚5mm,間隔 2mm,矩陣 320×224,FOV24cm×18cm,2次采集);T2WI(T R/TE,3600/114ms,層厚5mm,間隔2mm,矩陣416×224,FOV24cm×18cm,2次采集);T1-FLAIR增強與彌散加權成像(DWI)。DWI使用自旋回波平面序列,(T R/T E4800ms/73.4ms,層厚5mm,間隔2mm,矩陣 128×128,FOV24cm×24cm,2次采集,b值為0和1000s/mm2)。

兩名經(jīng)驗豐富的放射科醫(yī)師手工設置感興趣區(qū),在ADC圖中最低信號區(qū)測量病變的ADCmin值,測量三次,取平均值。rADCmin值為病變的ADCmin值與對側正常腦白質ADC值的比值。

3.統(tǒng)計學處理

采用SPSS16.0 統(tǒng)計軟件進行數(shù)據(jù)處理,所有計量資料用表示。采用Mann-Whitney檢驗分析LGG與RG之間的差異性;檢驗水準以P＜0.05為差異有統(tǒng)計學意義。ROC曲線分析用于診斷LGG的臨界值、敏感性和特異性。

結 果

LGG的平均rADCmin為1.465±0.357,高于RG(1.062±0.120)(P＜0.05)。ROC曲線下面積為0.912,當臨界值rADCmin=1.193時,診斷LGG的敏感性為 82.8%,特異性為100%(圖 1)。

討 論

膠質瘤是中樞神經(jīng)系統(tǒng)最常見的腫瘤,其中LGG腫瘤細胞分化良好,伴有較多的膠質纖維,并含有較多的微囊變。LGG的常規(guī)CT/MRI缺乏特異性,很容易與RG、不典型腦梗死、腦炎和脫髓鞘病變混淆[1-2];尤其是RG,與LGG的臨床和影像特征非常相似。RG是在感染、中毒、外傷、缺血缺氧、輻射等因素的刺激下發(fā)生的膠質細胞增生,屬良性病變[3-7]。RG在病理上主要表現(xiàn)為膠質細胞的增生、變性伴膠質瘢痕形成,常伴有各種炎性細胞浸潤。影像表現(xiàn)缺乏特異性,與LGG相似,兩者的鑒別很難[8-11],最終需病理確診。但是兩者的生物學行為差異很大,治療方案也明顯不同。

近年來,DWI與ADC值在中樞神經(jīng)系統(tǒng)的應用越來越廣泛。ADC值是通過DWI計算得來的變量參數(shù),利用細胞外水分子運動(布朗運動)的高斯分布特性進行成像,能夠提供正常腦與腦病變的解剖和生理信息[12-13]。研究已發(fā)現(xiàn),ADCmin值在膠質瘤與淋巴瘤、腦轉移瘤、各種囊性病變的鑒別診斷中具有重要價值[14-17],同時ADCmin值也可以區(qū)分膠質瘤的各種成分,包括腫瘤實質、囊變與壞死、瘤周水腫[18-20]。但是有關RG ADC值的報道很少,Hagen等[21]研究發(fā)現(xiàn)ADC值在區(qū)分血管源性水腫與RG方面存在價值,說明ADCmin值在區(qū)分細胞成分與囊性成分方面存在優(yōu)勢。研究發(fā)現(xiàn),細胞數(shù)量增加或體積增大,可提高細胞密度,使細胞外水分子的彌散空間減小,彌散受限,ADC值將減低[22-23]。本研究中,LGG的rADCmin值(1.465±0.357)大于 RG(1.062±0.120)(圖 2,3),說明LGG與RG盡管都有細胞密度增高,但兩者之間還是存在著差別,很可能是病理上的細微差別;LGG在病理上不同于RG的主要差別之一就是LGG存在較多的微囊變,細胞外空間增大,這很可能引起水分子彌散能力增強,引起ADC值的升高。有人研究發(fā)現(xiàn)由于高級別膠質瘤(high-grade glioma,HGG)實質部分的ADC值低于LGG實質部分的ADC值,就是因為前者的細胞密度大,細胞外空間減小,水分子彌散受限,所以利用ADC值與膠質瘤分級存在的負性關系,可以對膠質瘤的術前分級提供一定的參考價值[24-27]。同樣,淋巴瘤和髓母細胞瘤的細胞密度大,其ADC值遠小于膠質瘤[14,28]。已經(jīng)有報道,可以通過測量膠質瘤瘤周水腫的ADC值來研究顱內腫瘤的鑒別診斷,但目前存在爭議[15,20,29]。所以ADC值在中樞神經(jīng)系統(tǒng)疾病的診斷與鑒別診斷中扮演著相當重要的角色。本研究的限制:第一,由于膠質瘤有時成分不均勻,可以同時含有不同級別的成分,而用于分級的組織標本不一定就是rADCmin對應的腫瘤部分,容易造成分級偏差。第二,DWI技術以水分子的高斯分布為前提,不能真正反映細胞膜、大分子等腦內微結構的復雜性。

總之,由于rADCmin能夠反映LGG與RG在病理組成上的細微差別,所以rADCmin值在LGG與RG的鑒別診斷中能夠提供重要的臨床價值,有利于降低誤診率,提高患者的預后評估。

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