椎動脈及基底動脈之血行動力變化與後循環梗塞的關係

Abstract

因為臨床表徵的複雜多元，使得脊椎基底動脈的血管疾病長期以來被視為診斷上的難題。 若因任一脊椎動脈或基底動脈的血流量不足而產生的腦部症狀，於臨床上統稱為脊椎基底動脈循環不全。脊椎基底動脈循環不全可能會演變成後腦循環梗塞。而這樣的梗塞容易再發，尤其當病患具有該處血管的狹窄或發育不良的時候。 單側或雙側的脊椎動脈發育不良的狀況已被視為是後腦循環梗塞的一個危險因子；可是這樣的異常可能還伴隨其他的血管異狀，比如：該處血管的延長擴張及胎兒型後大腦動脈。 基於對後腦循環的臨床症狀以及血管疾病的興趣，我們採用了不同族群的回朔性對列研究加以分析。 第一組是關於脊椎基底動脈循環不全的病患研究。我們發現若穿顱超音波偵測到脊椎基底動脈的流速偏低時，暗示其後腦循環不足，並且這些病患有比較高的後腦梗塞比例，甚至連前腦梗塞的比例也較高。在這個分析中，我們注意到，若脊椎基底動脈血液流速低於15cm/sec，其後循環梗塞相對危險值為2.55倍;若脊椎基底動脈血液流速低於20cm/sec，其後循環梗塞相對危險值為1.75倍。 接下來針對後腦梗塞的病人做比較。在這個研究中，對於超音波判斷的異常值，我們採用了第一組研究中所得到的顱內血流數據(<20cm/sec)並加入了另一個危險因子的評估：脊椎動脈發育不良。在這個部分，我們證實了：脊椎動脈發育不良及顱內血流偏低的這些異常的確於後腦梗塞病患族群有明顯差異；中風分佈的區域也和顱內外血流不足的區域相呼應。此外，我們還發現，在這一組病患，脊椎基底動脈狹窄處的血液流速,在超音波測量出的數據,往往是流速偏低而並非增加。 在接下來的研究中,我們分析了椎動脈發育不良與脊椎基底動脈延長擴張(vertebrobasilar dolichoectasia)的臨床相關性與可能的致病機轉。79.36% 的脊椎基底動脈延長擴張病患共伴有椎動脈發育不良的這種血管異常。藉由Receiver Operating Characteristic (ROC) 曲線分析，發現當一大一小的椎動脈兩者間超音波測量血液流量的差異大於55.65 mL/min,其鑑別的AUC為0.786 或其兩者流量比例大於5.28 (中間值) 其鑑別的AUC為0.747 。 在第四組研究中，我們發現雙側椎動脈發育不良者伴有高比例(75%)的胎兒型後大腦動脈的發育。而雙側椎動脈發育不良者，其後腦梗塞的區域均為兩側性、多發性的；這些病患發病的年齡也比一般中風病患更年輕。 傳統上後腦循環的血流動力結構，認為應該由全體加總後所得的血流狀況來加以評估。常見的會多為加總兩側的椎動脈血流量評估，有時認為需要再加上來自脊柱動脈或前循環支援的後大腦動脈來的側枝循環。 但是在我們這些研究中發現，不論單側或雙側的椎動脈發育不良，其實對後腦梗塞都相當重要。而且在我們的研究中連結了椎動脈發育不良與這個區域先天及後天的血管畸形的互動關聯。所以臨床上，若發現有這些危險因子的病患，及早適時的藥物或手術矯正是有必要的。 在這些研究中，我們獲得了不同於傳統的腦部血管超音波的判斷標準。並將其與椎基底動脈循環不全，後腦梗塞，後腦血管狹窄以及脊椎基底動脈延長擴張做結合應用。 為證實這些標準在臨床上的準確性，更大規模的臨床案例分析實為必須。期待我們這些研究能幫助提升臨床診斷的敏感性。

The clinical presentation of vertebrobasilar vascular disorders varies and the diagnosis remains a challenge. The vertebrobasilar insufficiency (VBI) results from insufficient blood flow to the posterior portion of the brain due to restricted flow to either the vertebral or the basilar artery. VBI may evolve to posterior circulation infarction (PCI). PCI is at higher risk of early recurrent stroke especially in those with vertebrobasilar stenosis or hypoplasia. Unilateral or bilateral vertebral artery hypoplasia is considered as a risk factor for PCI; however, they are usually associated with different vascular disorders, such as dolichoectasia and fetal type PCA. In our studies, these clinical symptoms and vascular diseases are analyzed by retrospective cohort studies . In the first study of VBI, we found that low VB velocity noted by sonography reveals insufficient flow over posterior circulation and may indicate a higher risk of PCI, and even total ischemic stroke . Increased PCI risk was noted if the mean velocity of vertebrobasilar arteries is below than 15 cm/sec (adjusted odds ratio: 2.55, 95% confidence interval, 1.58-4.13; P<0.001) or 20 cm/sec (adjusted odds ratio: 1.75, 95% confidence interval, 1.14-2.66; P=0.009). In the 2nd study of posterior infarction patients, we adapted sonographic criteria getting from 1st study and added the VAH criteria for extracranial ultrasound analysis. Significant higher frequency of vertebral artery hypoplasia (VAH) and decreased intracranial vertebrobasilar velocity in PCI group (44.75% and 64.33%) is documented (P<0.0001 and P=0.035). Ischemic lesion distributions were correlated with VAH (55.56 %), low vertebral and basilar artery velocity (44.44%, 25.53%) documented by sonography. Low vertebrobasilar velocity is higher correlated with magnetic resonance imaging documented vascular stenosis (48.98%). In the 3rd study, we evaluated the clinical association and pathophysiology of unilateral VAH with vertebrobasilar dolichoectasia(VBD). In the group of VBD, 79.36% patients were found with the coexistence of VAH and VBD. In the group with VAH and VBD co-occurrence and VAH without VBD, Receiver Operating Characteristic (ROC) curve analysis showed a cut-off value of 55.65 mL/min in the differences in side-to-side extracranial vertebral artery flow volume on Doppler sonography, with an area under the curve (AUC) of 0.786 (sensitivity 90.0% ; specificity 62.6% ) indicating an acceptable discrimination. Side-to-side extracranial vertebral artery flow ratio (median) , ROC curve analysis showed an optimal threshold value of 5.28, with an AUC of 0.747(sensitivity 78.0% and specificity 66.1%). In the 4th study, bilateral VAH is found with high frequency (75%) of fetal variant posterior cerebral arteries. The infarction patterns of these patients were all bilateral and in multiple vascular territories. In this group, younger age at stroke onset was also found. Traditionally, the hemodynamic stability of posterior circulation is evaluated from the net Vertebral arterial flow, the collateral flow from spinal artery and combined with the anterior circulation from the posterior cerebral arteries , Our studies emphasized the importance of VAH , whatever unilateral or bilateral . We also connected the pathological evolution with VAH and intracranial vascular abnormalities. From the viewpoints of clinical practice, for patients with such risky characteristics , early medical prevention or surgical correction is suggested. New and applicable criteria for sonographic exam of vertebrobasilar insufficiency and dolichoectasia were analyzed in our studies. They are different from the previous criteria . We hope to get larger scale studies for these criteria and these criteria may be beneficial for a higher sensitivity in clinical diagnosis.