李劍秋 綜述,呂發(fā)金審校
(重慶醫(yī)科大學(xué)附屬第一醫(yī)院放射科 400016)
顱內(nèi)動(dòng)脈瘤是一種常見(jiàn)的腦血管病,人群發(fā)病率為3.6%~6%[1-2]。在蛛網(wǎng)膜下腔出血的患者中,約有68%為動(dòng)脈瘤破裂所致,其破裂的發(fā)生率(占動(dòng)脈瘤人群)為1%~2%[2],破裂后致殘、致死率很高。近年來(lái),隨著神經(jīng)影像學(xué)技術(shù)的發(fā)展和診斷水平的提高[3],顱內(nèi)動(dòng)脈瘤的檢出率不斷提高。但是,對(duì)顱內(nèi)動(dòng)脈瘤的治療,尤其是對(duì)未破裂動(dòng)脈瘤的治療仍存在爭(zhēng)議,加之開(kāi)顱夾閉術(shù)及介入栓塞術(shù)的手術(shù)風(fēng)險(xiǎn)大,因此,對(duì)顱內(nèi)動(dòng)脈瘤破裂風(fēng)險(xiǎn)評(píng)估的研究顯得尤為重要。動(dòng)脈瘤形態(tài)學(xué)特征的改變,可以反映其發(fā)生、發(fā)展及破裂過(guò)程,但其具體的預(yù)測(cè)價(jià)值尚存在爭(zhēng)議。近年來(lái),國(guó)內(nèi)外做了不少關(guān)于動(dòng)脈瘤形態(tài)學(xué)特征與破裂風(fēng)險(xiǎn)關(guān)系的研究。本文著重對(duì)影響動(dòng)脈瘤破裂的形態(tài)學(xué)因素作一綜述。
動(dòng)脈瘤的位置是導(dǎo)致動(dòng)脈瘤發(fā)生破裂的重要因素。Weir等[4]報(bào)道不同位置的動(dòng)脈瘤破裂概率分別為前交通和胼緣動(dòng)脈86%,基底動(dòng)脈77%,大腦中動(dòng)脈61%,后交通動(dòng)脈58%,眼動(dòng)脈65%。Marieke等[5]指出不同位置的動(dòng)脈瘤破裂RR及95%CI分別為頸內(nèi)動(dòng)脈0.8(0.3~2.8),大腦前動(dòng)脈0.7(0.4~1.5),大腦中動(dòng)脈0.4(0.2~1.0),后交通動(dòng)脈1.8(0.7~4.5),后循環(huán)0.8(0.3~2.8)。Sadatomo等[6]報(bào)道了44個(gè)大腦中動(dòng)脈瘤,發(fā)現(xiàn)在血管分叉處動(dòng)脈瘤更容易破裂。Huttunen等[7]研究認(rèn)為,未破裂動(dòng)脈瘤多見(jiàn)于大腦中動(dòng)脈分叉處。雖然文獻(xiàn)報(bào)道結(jié)果有差異,但前交通動(dòng)脈、后交通動(dòng)脈、大腦中動(dòng)脈和后循環(huán)動(dòng)脈是動(dòng)脈瘤的好發(fā)部位。還有大部分學(xué)者認(rèn)為后循環(huán)動(dòng)脈瘤破裂率高于前循環(huán)。Nahed等[8]研究認(rèn)為,在小于或等于7mm的動(dòng)脈瘤中,后循環(huán)的破裂率是前循環(huán)的3.5倍(P=0.048;95%CI:0.95~19.4)。同樣 White等[8]也指出,后循環(huán)動(dòng)脈瘤年破裂率高于其他部位脈瘤,且后循環(huán)動(dòng)脈瘤年破裂率與大小成正比,直徑小于或等于7、7~12、13~24、>25mm的后循環(huán)動(dòng)脈瘤年破裂率分別為0.5%、3.0%、3.7%和10%。Sato等[10]研究提出,動(dòng)脈瘤的大小、蛛網(wǎng)膜下腔出血病史及動(dòng)脈瘤位于后循環(huán)是預(yù)測(cè)動(dòng)脈瘤破裂的顯著危險(xiǎn)因子。Beck等[11]卻得到相反的結(jié)果,指出小于7mm的破裂動(dòng)脈瘤多位于前循環(huán)。
有關(guān)動(dòng)脈瘤的形狀與破裂的關(guān)系報(bào)道比較少。Raghavan等[12]認(rèn)為與動(dòng)脈瘤的大小相比,形狀可以更好地用來(lái)區(qū)分破裂動(dòng)脈瘤和未破裂動(dòng)脈瘤,但形狀能否預(yù)測(cè)動(dòng)脈瘤破裂風(fēng)險(xiǎn)還需要更深入的研究。Lauric等[13]運(yùn)用形狀預(yù)測(cè)模型分析了117個(gè)動(dòng)脈瘤,認(rèn)為形狀對(duì)動(dòng)脈瘤破裂危險(xiǎn)分層具有潛在的價(jià)值。Asari等[14]隨訪了72個(gè)未破裂動(dòng)脈瘤,22個(gè)多葉形中有7個(gè)發(fā)生破裂致蛛網(wǎng)膜下腔出血,50個(gè)單葉形中只有2個(gè),因此,多葉形未破裂動(dòng)脈瘤易發(fā)生破裂出血。破裂動(dòng)脈瘤和未破裂動(dòng)脈瘤在形狀上是有差異的,Rohde等[15]用傅立葉函數(shù)分析了45個(gè)未破裂動(dòng)脈瘤和46個(gè)破裂動(dòng)脈瘤的形狀,得出78%的破裂動(dòng)脈瘤表面是不光整的,從而得出動(dòng)脈瘤形態(tài)的不規(guī)則可能導(dǎo)致破裂風(fēng)險(xiǎn)增加的結(jié)論。近年來(lái),不少研究把瘤體長(zhǎng)度和瘤頸寬度的比值(aspect ratio,AR)作為預(yù)測(cè)動(dòng)脈瘤破裂風(fēng)險(xiǎn)的指標(biāo),大多數(shù)研究發(fā)現(xiàn)破裂動(dòng)脈瘤的AR值較未破裂動(dòng)脈瘤大,據(jù)此可以推測(cè)囊狀動(dòng)脈瘤(以窄的瘤頸與載瘤動(dòng)脈相連)破裂幾率較高,不過(guò),此結(jié)論有待進(jìn)一步研究證實(shí)。
國(guó)內(nèi)外許多文獻(xiàn)認(rèn)為動(dòng)脈瘤大小是動(dòng)脈瘤破裂最重要的因素之一。Inagawa等[16]對(duì)日本某地區(qū)285個(gè)囊狀破裂動(dòng)脈瘤的大小進(jìn)行回顧性分析,得出大于10mm的動(dòng)脈瘤再次出血的危險(xiǎn)性高于小于10mm的動(dòng)脈瘤。Amenta等[17]指出動(dòng)脈瘤破裂率最高時(shí)大小小于10mm。Lai等[18]回顧性分析了中國(guó)香港267例蛛網(wǎng)膜下腔出血的顱內(nèi)動(dòng)脈瘤患者影像資料,得出64%破裂動(dòng)脈瘤直徑小于或等于5mm。Beck等[11]通過(guò)對(duì)155個(gè)囊狀動(dòng)脈瘤的研究,得出大部分破裂動(dòng)脈瘤的最大高度和最大寬度分別小于10.7mm,并指出動(dòng)脈瘤大小在4~9 mm范圍者最容易破裂。Carter等[19]測(cè)量了854個(gè)破裂動(dòng)脈瘤及815個(gè)未破裂動(dòng)脈瘤的大小,發(fā)現(xiàn)血管末端的破裂動(dòng)脈瘤和小腦后下動(dòng)脈破裂動(dòng)脈瘤的平均大小分別為5.7mm(95%CI:4.8~6.5)和7.1mm(95%CI:6.3~7.8),小于基底動(dòng)脈、大腦中動(dòng)脈和發(fā)生在Willis環(huán)的頸內(nèi)動(dòng)脈瘤的平均大小。Rahman等[20]運(yùn)用2D血管造影的方法,對(duì)動(dòng)脈瘤大小與破裂的相關(guān)性做了一項(xiàng)前瞻性的研究。其中破裂動(dòng)脈瘤16個(gè),未破裂動(dòng)脈瘤24個(gè),結(jié)果顯示未破裂動(dòng)脈瘤的瘤體平均最大值約(6.18±0.60)mm小于破裂動(dòng)脈瘤的平均最大值(7.91±0.47)mm。Jeong等[21]對(duì)336例破裂動(dòng)脈瘤進(jìn)行研究,得出大腦前動(dòng)脈、頸內(nèi)動(dòng)脈、大腦中動(dòng)脈和基底動(dòng)脈破裂動(dòng)脈瘤的平均直徑分別為(5.47±2.536)、(6.84±3.941)、(7.09±3.652)mm和(6.21±3.369 7)mm。Huttunen等[7]指出破裂動(dòng)脈瘤大小的判斷更取決于血流的壓力??梢?jiàn),動(dòng)脈瘤的大小與研究病例的地區(qū)和范圍有關(guān)系,亞洲人和歐洲人可能存在差異,還與患者年齡、性別和自身疾病等綜合因素有關(guān),因此,應(yīng)開(kāi)展多因素綜合研究。
動(dòng)脈瘤瘤頸對(duì)于控制進(jìn)入動(dòng)脈瘤內(nèi)的血流量有重要作用。目前,對(duì)瘤頸與動(dòng)脈瘤破裂之間的關(guān)系研究較少,但瘤頸寬度對(duì)動(dòng)脈瘤手術(shù)方式的選擇具有較大的臨床價(jià)值。Hassan等[22]和Hoh等[23]發(fā)現(xiàn)破裂與未破裂動(dòng)脈瘤平均瘤頸寬度均在2~3mm之間,差異無(wú)統(tǒng)計(jì)學(xué)意義(P>0.05)。但大部分研究證實(shí)瘤頸寬度與動(dòng)脈瘤破裂有關(guān)系。You等[24]對(duì)未破裂動(dòng)脈瘤的特點(diǎn)進(jìn)行研究,從而預(yù)測(cè)動(dòng)脈瘤破裂的危險(xiǎn)因素。他們將290個(gè)動(dòng)脈瘤進(jìn)行分組對(duì)照研究,其中破裂組167個(gè),未破裂組123個(gè),得出最大瘤頸寬度小于或等于3mm(OR 2.56)與動(dòng)脈瘤破裂密切相關(guān)(P<0.05)。Rohde等[15]比較了46個(gè)破裂動(dòng)脈瘤和45個(gè)未破裂動(dòng)脈瘤的瘤頸寬度,分別為3.0mm和4.0mm。Beck等[11]通過(guò)3D血管造影對(duì)破裂動(dòng)脈瘤(83個(gè))與未破裂動(dòng)脈瘤(72個(gè))研究顯示,69.4%破裂動(dòng)脈瘤的瘤頸寬度在4~6mm之間。
AR值即瘤體長(zhǎng)度/瘤頸寬度,在評(píng)價(jià)動(dòng)脈瘤的破裂風(fēng)險(xiǎn)中具有良好的敏感度及特異度。Dhar等[25]指出,AR值是一項(xiàng)評(píng)價(jià)動(dòng)脈瘤破裂很好的形態(tài)學(xué)指標(biāo),但未對(duì)AR值與破裂風(fēng)險(xiǎn)的相關(guān)性做進(jìn)一步研究。Hoh等[23]得出AR值越大越易導(dǎo)致動(dòng)脈瘤破裂,但也有得出相反結(jié)論的,Beck等[11]則認(rèn)為AR值越小動(dòng)脈瘤越容易破裂。AR值作為評(píng)價(jià)動(dòng)脈瘤破裂的指標(biāo)尚具有一定的局限性,各個(gè)研究的結(jié)果不盡相同,沒(méi)有得出一個(gè)可靠的臨界值。Nader-Sepahi等[26]研究得出破裂動(dòng)脈瘤的平均AR值為2.7,而未破裂動(dòng)脈瘤的平均AR值為1.8。Sadatomo等[6]得出的結(jié)論是破裂動(dòng)脈瘤的平均AR值為2.24,而未破裂動(dòng)脈瘤的平均AR值為1.56,AR值大于或等于1.8動(dòng)脈瘤更容易破裂。Amenta等[17]分析了5 134個(gè)顱內(nèi)動(dòng)脈瘤(34.90%為破裂動(dòng)脈瘤),得出AR>1.6動(dòng)脈瘤破裂率較高。
SR值即瘤體長(zhǎng)度/載瘤動(dòng)脈直徑,由Dhar等[25]首次提出,可以把SR作為評(píng)估動(dòng)脈瘤破裂的一項(xiàng)新指標(biāo)。Rahman等[20]研究指出,通過(guò)2D血管造影技術(shù)可以很清楚地觀察顱內(nèi)動(dòng)脈瘤瘤體及載瘤動(dòng)脈情況,從而準(zhǔn)確計(jì)算SR值,并得出SR值與動(dòng)脈瘤破裂有關(guān),但SR值對(duì)動(dòng)脈瘤破裂風(fēng)險(xiǎn)的預(yù)測(cè)還需在進(jìn)一步多病例的前瞻性研究中得到證實(shí)。Ma等[27]回顧性研究38個(gè)經(jīng)3D血管造影證實(shí)的顱內(nèi)動(dòng)脈瘤,其中16個(gè)破裂,對(duì)其SR值進(jìn)行Logistic回歸模型分析,SR值的優(yōu)勢(shì)比為3.52(P=0.04;95%CI:1.035~11.938),結(jié)果表明SR值與動(dòng)脈瘤破裂有較強(qiáng)的關(guān)聯(lián)性,可以作為評(píng)價(jià)動(dòng)脈瘤破裂的重要指標(biāo)。Tremmel等[28]得出77%破裂動(dòng)脈瘤的SR值大于2,而83%未破裂動(dòng)脈瘤SR值小于或等于2。Sadatomo等[6]研究顯示,破裂動(dòng)脈瘤的平均SR值為1.53,而未破裂動(dòng)脈瘤的平均SR值為2.14,SR值小于或等于1.7,動(dòng)脈瘤更容易破裂。
子囊也是判斷破裂動(dòng)脈瘤的重要根據(jù)之一,且它同時(shí)也是將破裂的重要危險(xiǎn)信號(hào),Meng等[29]對(duì)子囊的形成提出一種假設(shè),認(rèn)為是血管的自我保護(hù)機(jī)制,由于動(dòng)脈瘤是由薄弱的血管壁局限性擴(kuò)張而形成的,所以瘤壁比正常血管壁薄,而子囊是由主瘤體向外擴(kuò)張而成,因此,新生子囊壁更加薄弱,加上其他血流動(dòng)力學(xué)等相關(guān)因素,易導(dǎo)致動(dòng)脈瘤破裂。Sadatomo等[6]研究也認(rèn)為,子囊形成對(duì)動(dòng)脈瘤破裂存在影響。Zhang等[30]對(duì)54個(gè)動(dòng)脈瘤(69個(gè)子囊)的血流動(dòng)力學(xué)研究發(fā)現(xiàn),子囊與主瘤體相比,具有更低的壁切應(yīng)力(WSS)和更高的振蕩切變指數(shù)。Cebral等[31]研究也顯示,低的壁切應(yīng)力是子囊形成的原因,這些因素都會(huì)增加動(dòng)脈瘤的破裂率。
顱內(nèi)血管變異與動(dòng)脈瘤的發(fā)生、發(fā)展關(guān)系密切,血管變異將引起血流動(dòng)力學(xué)的改變,而血流動(dòng)力學(xué)的改變又是引起動(dòng)脈瘤破裂的重要因素,所以血管變異可能與動(dòng)脈瘤的破裂存在關(guān)系,但這尚需更加深入的研究。以前交通動(dòng)脈復(fù)合體為例,此處變異較多,并以大腦前動(dòng)脈A1段缺如多見(jiàn),當(dāng)A1段發(fā)生缺如變異時(shí),缺如側(cè)頸內(nèi)動(dòng)脈僅供應(yīng)該側(cè)的大腦中動(dòng)脈瘤致血流量減少,而相應(yīng)的缺如對(duì)側(cè)頸內(nèi)動(dòng)脈供應(yīng)該側(cè)大腦中動(dòng)脈及雙側(cè)大腦前動(dòng)脈致血量增加,從而引起血流動(dòng)力學(xué)改變[32]。Alnaes等[33]研究表明,大腦前動(dòng)脈A1段變異與前交通動(dòng)脈瘤關(guān)系緊密,以左側(cè)A1段優(yōu)勢(shì)多見(jiàn),前交通動(dòng)脈瘤偏左側(cè)也較多見(jiàn)。范曉等[34]發(fā)現(xiàn)前交通動(dòng)脈瘤的形成與 Willis環(huán)變異有關(guān),后交通動(dòng)脈瘤的形成與Willis環(huán)變異的關(guān)系尚不明了。
綜上,目前對(duì)于動(dòng)脈瘤的形態(tài)學(xué)特征和破裂風(fēng)險(xiǎn)的關(guān)系的研究雖然不少,但大部分為回顧性研究,動(dòng)脈瘤破裂前、后形態(tài)和大小可能發(fā)生變化,這給動(dòng)脈瘤形態(tài)參數(shù)測(cè)量帶來(lái)誤差。且很少對(duì)未破裂動(dòng)脈瘤進(jìn)行隨訪,這樣可能會(huì)漏掉隨訪過(guò)程中破裂的動(dòng)脈瘤,動(dòng)脈瘤的破裂率會(huì)隨時(shí)間發(fā)生變化[35]。加之,國(guó)內(nèi)外相關(guān)文獻(xiàn)中提到的各個(gè)形態(tài)學(xué)指標(biāo)評(píng)價(jià)結(jié)果有所不同,尚未得到統(tǒng)一的可靠的臨界值,因此,在今后動(dòng)脈瘤形態(tài)學(xué)特征與破裂風(fēng)險(xiǎn)的關(guān)系的研究中,需要大樣本前瞻性的研究,定期進(jìn)行隨訪,這樣才能準(zhǔn)確地對(duì)動(dòng)脈瘤破裂的危險(xiǎn)程度進(jìn)行分層,為動(dòng)脈瘤患者提供更加完善的術(shù)前評(píng)估。
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