神經(jīng)監(jiān)測技術(shù)在甲狀腺手術(shù)中幫助識別喉上神經(jīng)外支的臨床意義

張軍 綜述 高明 審校

喉上神經(jīng)外支（external branch of the superior la?ryngeal nerve，EBSLN）損傷是甲狀腺癌手術(shù)并發(fā)癥之一，該神經(jīng)損傷引起聲音嘶啞、發(fā)聲疲勞、聲頻范圍降低等癥狀，導(dǎo)致語言溝通障礙、工作能力下降，嚴重影響患者的生存質(zhì)量［1］。甲狀腺癌手術(shù)中是否對喉上神經(jīng)外支進行常規(guī)的識別一直存在諸多的爭議，經(jīng)驗性的認為通過被膜的精細操作，緊鄰甲狀腺上極骨骼化游離及單支鉗夾切斷甲狀腺上極血管足以保護喉上神經(jīng)免受損傷。美國甲狀腺醫(yī)師協(xié)會（ATA）指南最新版建議在解剖甲狀腺上極時要對喉上神經(jīng)外支進行肉眼識別以達到保護神經(jīng)的目的。甲狀腺癌手術(shù)導(dǎo)致喉上神經(jīng)外支損傷十分常見，國外文獻報道甲狀腺術(shù)后喉上神經(jīng)外支永久性損傷的發(fā)生率為0.3%～3.5%，暫時性損傷的發(fā)生率高達58%［2-5］。由于不同研究中使用的方法不同及數(shù)據(jù)有限，喉上神經(jīng)外支損傷的確切概率很難評價。鑒于損傷后聲音癥狀的改變較為輕微，術(shù)后喉鏡的改變各有不同，環(huán)甲肌的肌電圖表現(xiàn)是診斷喉上神經(jīng)外支損傷的唯一方法［6］。國際神經(jīng)監(jiān)測學(xué)組（INMSG）已將術(shù)中神經(jīng)監(jiān)測視為幫助肉眼識別神經(jīng)的“金標準”，而且此項技術(shù)也可同時應(yīng)用于甲狀腺癌手術(shù)中喉返神經(jīng)和喉上神經(jīng)外支的識別。

1 喉上神經(jīng)外支的解剖

喉上神經(jīng)是迷走神經(jīng)節(jié)發(fā)出的分支，沿頸動脈的后方下行約2 cm到達舌骨大角平面，于頸內(nèi)動脈及頸外動脈分叉處的深面或頸內(nèi)動脈的深面分為內(nèi)外兩支。內(nèi)支為感覺神經(jīng)，外支屬運動神經(jīng)。內(nèi)支和喉上動靜脈伴行，穿過舌甲膜后分布于聲門上區(qū)黏膜，傳遞該處黏膜感覺。外支通常與頸內(nèi)動脈的內(nèi)側(cè)緣或頸總動脈的后方形成交叉，在甲狀腺上動脈的后方及頸中交感神經(jīng)節(jié)的內(nèi)側(cè)下降，最終與動脈伴行，自咽下縮肌與胸骨甲狀肌形成的通道進入環(huán)甲肌，支配環(huán)甲肌運動［7］。其于咽下縮肌與胸骨甲狀腺肌在甲狀軟骨斜線上附著處之間通過，然后穿過咽下縮肌［8］。在甲狀軟骨上角水平喉上神經(jīng)外支稍轉(zhuǎn)向內(nèi)側(cè)，與甲狀軟骨斜線平行，下行時靠近甲狀軟骨下緣突起隨后轉(zhuǎn)向內(nèi)側(cè)進入環(huán)甲肌。喉上神經(jīng)行徑路線左右兩側(cè)無明顯差異，喉上神經(jīng)外支直徑約0.8 mm，其總長度為8.0～8.9 cm［9］。

2 喉上神經(jīng)外支分型及變異

喉上神經(jīng)外支與甲狀腺上動脈和甲狀腺上極的關(guān)系分為：1型：喉上神經(jīng)外支與甲狀腺上動脈交叉點距離甲狀腺上極＞1 cm；2a型：交叉點距離甲狀腺上極≤1 cm；2b型：交叉點靠近甲狀腺上極或位于上極以下［10］。喉上神經(jīng)外支分型與甲狀腺的體積關(guān)系密切，在甲狀腺體積正常的人群中各型比例依次為68%、18%、14%，在甲狀腺發(fā)生病理性腫大時各型比例依次為23%、15%、54%。2a型、2b型由于位置較低，在解剖和分離甲狀腺上極的血管時更容易損傷［11］。中國學(xué)者解剖86條喉上神經(jīng)外支發(fā)現(xiàn)中國人各型比例分別為1型占16.2%、2a型占39.5%、2b型占38.3%，2a、2b型的比例高達 77.8%［12］。韓國Hwang等［13］術(shù)中行神經(jīng)監(jiān)測識別喉上神經(jīng)外支92條，發(fā)現(xiàn)1型占16.3%、2a型占56.5%、2b型占27.2%，2a、2b型的比例高達83.7%。以上報道認為喉上神經(jīng)損傷風(fēng)險高于西方報道的數(shù)據(jù)，不同種族的人群喉上神經(jīng)外支的解剖變異較大。Pradeep等［14］認為即使種族相同，喉上神經(jīng)的變異仍較大。而且隨著腺體的增大2型的比例增大，損傷的概率更高。在那些甲狀腺體積增大或短頸的患者中解剖甲狀腺上極顯得更加困難，喉上神經(jīng)外支受到損傷的風(fēng)險更大。在這些情況下，甲狀腺上極的上界明顯提高導(dǎo)致了神經(jīng)與甲狀腺上極的粘連。Cernea等［15-16］研究描述當(dāng)患者甲狀腺重量超過100 g時，最容易被損傷的2b型神經(jīng)所占的比例將高達54%。Furlan等［17］也得到了相似的結(jié)論，其根據(jù)喉神經(jīng)外支與甲狀腺的解剖關(guān)系分析了喉上神經(jīng)外支損傷一些內(nèi)在的危險因素。根據(jù)72例成人尸體頸部解剖發(fā)現(xiàn)，患者短頸或者甲狀腺體積較大是喉上神經(jīng)外支損傷的危險因素。Friedman等［18］研究發(fā)現(xiàn)有將近20%的喉上神經(jīng)外支不能被肉眼識別，因為其終末端全部被咽下縮肌所覆蓋。在大多數(shù)情況下這些神經(jīng)只能通過沿著咽下縮肌和環(huán)甲肌進行神經(jīng)刺激才能識別。近期有研究認為肥胖患者肉眼辨別喉上神經(jīng)難度較大而其他因素并無影響［19］。除此之外，喉上神經(jīng)外支易與下列結(jié)構(gòu)混淆：1）纖細的非神經(jīng)纖維；2）環(huán)甲肌或咽下縮肌的肌腱纖維；3）調(diào)節(jié)來自環(huán)甲關(guān)節(jié)沖動的傳入神經(jīng)纖維與環(huán)甲膜內(nèi)黏膜之間少見的交通支。喉上神經(jīng)外支的識別與保護在甲狀腺外科手術(shù)存在諸多困難，那么臨床有必要將術(shù)中神經(jīng)監(jiān)測技術(shù)應(yīng)用到甲狀腺癌手術(shù)中去幫助識別和保護喉上神經(jīng)外支［20］。

3 喉上神經(jīng)外支術(shù)中神經(jīng)監(jiān)測在臨床上的應(yīng)用

喉上神經(jīng)外支術(shù)中神經(jīng)監(jiān)測中的麻醉方法、設(shè)備設(shè)置、氣管插管位置以及對電極管正確位置的驗證方法均與喉返神經(jīng)監(jiān)測的方法相同［21］。監(jiān)視器設(shè)置事件閾值通常為100 uV（或者較上述值低），刺激探針電流強度應(yīng)常規(guī)設(shè)定為1～2 mA。為了確認已被肉眼識別的喉上神經(jīng)外支，目前應(yīng)使用的刺激電流強度為1 mA。但若為了標測出喉上神經(jīng)外支的行徑路線，應(yīng)使用較高的刺激電流強度為2 mA，并通過一個靈活的探針傳送頻率40 kHz的電脈沖刺激。近期有研究認為刺激胸骨甲狀肌-喉三角可快速有效的監(jiān)測喉上神經(jīng)外支情況［22-23］。喉上神經(jīng)外支在受到探針刺激后會出現(xiàn)兩種陽性結(jié)果：1）環(huán)甲肌出現(xiàn)震顫（出現(xiàn)在所有的患者）；2）通過氣管內(nèi)導(dǎo)管電極記錄到的聲帶去極化聲門肌電圖反應(yīng)（出現(xiàn)在70%～80%的患者）［6］。Potenza等［24］研究發(fā)現(xiàn)刺激喉上神經(jīng)外支引起環(huán)甲肌震顫的陽性率為100%，而出現(xiàn)的肌電圖反應(yīng)陽性率為80%。Uludag等［25］研究也得出相似的結(jié)論。隨著設(shè)備靈敏度提高以及技術(shù)的進步，神經(jīng)監(jiān)測技術(shù)將更加有效地識別和記錄喉上神經(jīng)受刺激所形成波形以及檢測前聲門的去極化水平，肌電圖的診斷率將進一步提高。

近幾年的文獻報道使用術(shù)中神經(jīng)監(jiān)測確實提高了喉上神經(jīng)外支的識別率，降低了神經(jīng)被誤傷的風(fēng)險。一項腔鏡輔助下甲狀腺癌手術(shù)研究中，Dionigi等［26］隨機將72例患者分為兩組，研究結(jié)果表明在使用術(shù)中神經(jīng)監(jiān)測組中喉上神經(jīng)外支的識別率為83.6%，在未使用術(shù)中神經(jīng)監(jiān)測的對照組中喉上神經(jīng)外支的識別率僅為42%。Lifante等［27］研究47例患者69條高危的喉上神經(jīng)外支，結(jié)果發(fā)現(xiàn)通過神經(jīng)監(jiān)測喉上神經(jīng)外支的識別率為65%，未使用神經(jīng)監(jiān)測喉上神經(jīng)外支的識別率為33%。Barczyński等［28］的前瞻性隨機對照試驗對喉上神經(jīng)外支的神經(jīng)監(jiān)測有較詳細的記錄，該試驗共入組210例患者，發(fā)現(xiàn)通過觀察肌電圖反應(yīng)和監(jiān)視器的可聽訊號可以增加喉上神經(jīng)外支的識別率，其記錄的結(jié)果是使用術(shù)中神經(jīng)監(jiān)測喉上神經(jīng)外支的識別率為83.8%，未使用術(shù)中神經(jīng)監(jiān)測喉上神經(jīng)外支的識別率為34.3%。該研究在術(shù)前術(shù)后通過電視喉鏡、最大發(fā)聲時間、音調(diào)、基本頻率以及聲音質(zhì)量評分（GRBAS）對患者的聲音進行了綜合評價。得出的結(jié)論是在甲狀腺癌手術(shù)中使用術(shù)中神經(jīng)監(jiān)測能夠有效提高喉上神經(jīng)外支的識別率，同時也能降低甲狀腺術(shù)后早期聲音改變的風(fēng)險。Glover等［29］為了研究使用神經(jīng)監(jiān)測術(shù)的喉上神經(jīng)外支的識別率和單純解剖技術(shù)喉上神經(jīng)外支識別率的差別，對228例甲狀腺手術(shù)患者（129例甲狀腺全切術(shù)，99例次全切術(shù)）進行觀察。在357例具有潛在受損風(fēng)險的喉上神經(jīng)外支中，使用神經(jīng)監(jiān)測幫助的識別率為97.2%，而通過單純解剖技術(shù)進行肉眼識別的概率為85.7%。所有識別的喉上神經(jīng)外支在結(jié)扎甲狀腺上極血管后均對神經(jīng)電刺激確保觀察到環(huán)甲肌震顫。其得出的結(jié)論是通過神經(jīng)監(jiān)測和甲狀腺上極的精細解剖可以提高喉上神經(jīng)外支的識別率。由于在甲狀腺癌手術(shù)中喉上神經(jīng)外支很容易損傷并引起聲音的改變，神經(jīng)監(jiān)測能夠幫助識別喉上神經(jīng)外支，同時還能在甲狀腺切除術(shù)后對喉上神經(jīng)外支的功能進行評價。近期研究同樣表明，神經(jīng)監(jiān)測可識別93.1%～97.5%的喉上神經(jīng)外支病例，且可有效降低喉上神經(jīng)外支損傷率［20，30］。近年有研究發(fā)現(xiàn)應(yīng)用機器人手術(shù)技術(shù)行甲狀腺切除術(shù)時，加用神經(jīng)監(jiān)測技術(shù)可有效減低喉上神經(jīng)損傷率，將神經(jīng)監(jiān)測技術(shù)與機器人手術(shù)技術(shù)結(jié)合治療甲狀腺癌的前景廣闊［31］。

4 結(jié)語

喉上神經(jīng)外支纖細、解剖復(fù)雜多變且與甲狀腺上動脈關(guān)系密切。在甲狀腺癌手術(shù)中喉上神經(jīng)外支僅靠肉眼辨別、暴露、分離出來十分困難且危險，術(shù)中神經(jīng)監(jiān)測能顯著提高喉上神經(jīng)外支的識別率。盡管術(shù)中神經(jīng)監(jiān)測無法取代熟練的外科解剖技術(shù)，隨著術(shù)中神經(jīng)監(jiān)測設(shè)備的不斷改進、標準化操作步驟的嚴格實施和監(jiān)測經(jīng)驗的不斷積累，必將在甲狀腺外科中發(fā)揮重要的臨床意義。

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