胡步宏 賈中正 耿道穎

低級別膠質(zhì)瘤(low-grade glioma,LGG)與反應(yīng)性膠質(zhì)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(zhì)瘤,甚至是膠質(zhì)母細(xì)胞瘤。一旦診斷為LGG,必須盡早手術(shù)切除。RG是膠質(zhì)細(xì)胞在數(shù)量上的增加,很少惡變(即使惡變成膠質(zhì)瘤,也需要很長時(shí)間),所以RG只需要隨訪,不需要手術(shù)。因此,LGG與RG的準(zhǔn)確鑒別對于患者的治療計(jì)劃與預(yù)后評估異常重要。近年來有關(guān)膠質(zhì)瘤表觀彌散系數(shù)(ADC)值的研究報(bào)道越來越多。因此,我們設(shè)想ADC值在鑒別LGG與RG方面可能存在價(jià)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(jià)值。

方 法

1.臨床資料

收集經(jīng)病理證實(shí)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(jìn)行過干預(yù)治療,每例患者均在MRI檢查后一周內(nèi)手術(shù)。

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(jìn)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(qiáng)與彌散加權(quán)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(yàn)豐富的放射科醫(yī)師手工設(shè)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(cè)正常腦白質(zhì)ADC值的比值。

3.統(tǒng)計(jì)學(xué)處理

采用SPSS16.0 統(tǒng)計(jì)軟件進(jìn)行數(shù)據(jù)處理,所有計(jì)量資料用表示。采用Mann-Whitney檢驗(yàn)分析LGG與RG之間的差異性;檢驗(yàn)水準(zhǔn)以P＜0.05為差異有統(tǒng)計(jì)學(xué)意義。ROC曲線分析用于診斷LGG的臨界值、敏感性和特異性。

結(jié) 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(dāng)臨界值rADCmin=1.193時(shí),診斷LGG的敏感性為 82.8%,特異性為100%(圖 1)。

討 論

膠質(zhì)瘤是中樞神經(jīng)系統(tǒng)最常見的腫瘤,其中LGG腫瘤細(xì)胞分化良好,伴有較多的膠質(zhì)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(zhì)細(xì)胞增生,屬良性病變[3-7]。RG在病理上主要表現(xiàn)為膠質(zhì)細(xì)胞的增生、變性伴膠質(zhì)瘢痕形成,常伴有各種炎性細(xì)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(xué)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(yīng)用越來越廣泛。ADC值是通過DWI計(jì)算得來的變量參數(shù),利用細(xì)胞外水分子運(yùn)動(dòng)(布朗運(yùn)動(dòng))的高斯分布特性進(jìn)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(zhì)瘤與淋巴瘤、腦轉(zhuǎn)移瘤、各種囊性病變的鑒別診斷中具有重要價(jià)值[14-17],同時(shí)ADCmin值也可以區(qū)分膠質(zhì)瘤的各種成分,包括腫瘤實(shí)質(zhì)、囊變與壞死、瘤周水腫[18-20]。但是有關(guān)RG ADC值的報(bào)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(jià)值,說明ADCmin值在區(qū)分細(xì)胞成分與囊性成分方面存在優(yōu)勢。研究發(fā)現(xiàn),細(xì)胞數(shù)量增加或體積增大,可提高細(xì)胞密度,使細(xì)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(xì)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(xì)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(xì)胞外空間增大,這很可能引起水分子彌散能力增強(qiáng),引起ADC值的升高。有人研究發(fā)現(xiàn)由于高級別膠質(zhì)瘤(high-grade glioma,HGG)實(shí)質(zhì)部分的ADC值低于LGG實(shí)質(zhì)部分的ADC值,就是因?yàn)榍罢叩募?xì)胞密度大,細(xì)胞外空間減小,水分子彌散受限,所以利用ADC值與膠質(zhì)瘤分級存在的負(fù)性關(guān)系,可以對膠質(zhì)瘤的術(shù)前分級提供一定的參考價(jià)值[24-27]。同樣,淋巴瘤和髓母細(xì)胞瘤的細(xì)胞密度大,其ADC值遠(yuǎn)小于膠質(zhì)瘤[14,28]。已經(jīng)有報(bào)道,可以通過測量膠質(zhì)瘤瘤周水腫的ADC值來研究顱內(nèi)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(dāng)重要的角色。本研究的限制:第一,由于膠質(zhì)瘤有時(shí)成分不均勻,可以同時(shí)含有不同級別的成分,而用于分級的組織標(biāo)本不一定就是rADCmin對應(yīng)的腫瘤部分,容易造成分級偏差。第二,DWI技術(shù)以水分子的高斯分布為前提,不能真正反映細(xì)胞膜、大分子等腦內(nèi)微結(jié)構(gòu)的復(fù)雜性。

總之,由于rADCmin能夠反映LGG與RG在病理組成上的細(xì)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(jià)值,有利于降低誤診率,提高患者的預(yù)后評估。

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