Introduction
Tortuosity of blood vessels is a common angiographic finding, which can occur in every organ system [
1,
2]. Increased tortuosity results from changes in mechanical factors of blood flow, such as elevated blood pressure [
3], reduced axial tension and artery elongation [
1]. It was also proved to be associated with systemic diseases, such as arterial hypertension [
3] and diabetes mellitus [
4]. Additionally, as tortuosity can be caused by vessel wall weakening, its increase can indicate the presence of vascular pathologies [
5,
6].
Higher arterial tortuosity promotes haemodynamic changes of blood flow. Tortuous arteries are characterised by decreased perfusion pressure, lower wall shear stress (WSS) and prolonged relative residence time (RRT) [
7]. Such changes in haemodynamics cause vessel wall impairment [
8,
9], which might lead to aneurysm development. In other studies, higher tortuosity was linked to aortic aneurysm presence and risk of rupture [
10], as well as to development of splenic artery aneurysm [
11]. In our previous study, we have also proved that aneurysms of the middle cerebral artery (MCA) [
12], anterior communicating artery (ACA) [
13] and internal carotid artery (ICA) [
14] are also linked to its tortuosity. However, these associations differed in terms of all used tortuosity descriptors. Therefore, we decided to similarly analyse tortuosity of the basilar artery (BA) to determine its relation with the presence and risk of aneurysm rupture.
Discussion
In our study, we found a significant association between age and BA tortuosity. A similar association was found in studies concerning coronary arteries [
17] and retinal vessels [
18]. In terms of cerebral arteries, increase of tortuosity with age was shown for the carotid artery [
19] and white matter arterioles [
20]. Such correlation is most likely associated to degenerative changes in arterial walls [
4,
21], as well as to higher probability of cardiovascular comorbidities.
Another finding of our study was the significant association of SOAM, TI, PAD and ICM with the presence of BA aneurysm. Kim et al in their study [
22] also found such correlation. It was shown before for aortic [
10] and splenic artery [
11] aneurysms. In terms of other cerebral vessels, a similar association was found for ICA [
14,
23], MCA [
12], ACoA [
13] and VA [
24]. Additionally, increased tortuosity was associated with lower risk of intracranial aneurysm rupture [
25] and inversely correlated with its size [
13]. The association of higher tortuosity with aneurysm development most likely results from weakening of the arterial wall. The study of Rikhtegar et al showed that higher tortuosity of coronary arteries results in lower WSS and prolonged RRT [
7]. Both of these changes could promote endothelial proinflammatory response and therefore lead to atherosclerotic changes in arterial walls [
8,
26]. The weakening of arterial wall resulting from atherosclerotic plaques might further contribute to aneurysm development [
8,
9]. The association of lower WSS and aneurysm formation was proved before by other authors [
27]. The fact that cerebral atherosclerosis was associated with MCA tortuosity also proves such theory [
28]. Lower WSS can additionally contribute to matrix metalloproteinases activation [
29], which results in remodelling of the arterial wall [
30]. Also, increased tortuosity might be caused by elevated blood pressure [
3] and blood flow [
31], which are considered risk factors for aneurysm development.
An interesting finding of this and our previous studies, in which we analysed tortuosity of MCA, ACA and ICA [
12‐
14,
25], are differences in contribution of certain tortuosity descriptors to risk of aneurysm development. For all four arteries, we found that increased values of TI were associated with higher risk of aneurysm presence. We also found that TI was inversely correlated with aneurysm dome size [
25]. In terms of SOAM and PAD, these factors were significantly lower among patients with MCA aneurysms, but significantly higher for other cerebral aneurysmal arteries. Also, ICM was significantly higher and RL significantly lower for patients with MCA and ICA aneurysms. On the other hand for patients with anterior communicating artery aneurysms, RL of ACA was significantly higher. The fact that we were unable to find a significant association between RL and BA aneurysm presence suggests that angles and inflexion points have more influence on aneurysm development risk than just deviation from straight line. Opposite to MCA, ACA and ICA course, natural BA course is straight; therefore, substantial lowering of RL can be caused by BA shaped like a single arch, which influences haemodynamics less than multiple angles. Also, as written in the study concerning ACA [
14], RL might not be a suitable tortuosity descriptor for the intracranial arteries. In terms of opposite findings of SOAM influence on MCA and BA aneurysm presence, it is known that both lower and higher WSS might contribute to arterial wall disfunction leading to aneurysm formation [
27]. Another explanation of differences between this study and studies concerning other cerebral arteries is the fact that posterior cerebral circulation is characterised by lower blood flow [
32] than anterior circulation and worse sympathetic innervation [
33], which ensures cerebral autoregulation. Therefore, due to different haemodynamics characteristic BA and other intracranial arteries might differ in susceptibility to WSS changes and arterial wall damage. Also, the study of Qiao et al showed the higher remodelling rate of atherosclerotic plaques in posterior circulation [
34], which could further indicate the more significant role of atherosclerosis on aneurysm formation in that location. Additionally, the fact that influence of certain tortuosity descriptors on aneurysm presence is most similar between ICA and BA might suggest the role of artery diameter in that association.
We also found a significant positive correlation between VA, PCA and BA dimensions and BA tortuosity. A similar correlation was also found in studies concerning coronary arteries [
35]. An explanation for such a finding could be the fact that both artery diameters [
35] and BA bifurcation angle [
36] increase with age, which is also related to tortuosity. Larger artery diameters could also indicate its walls weakening, as well as larger blood flow, which also promotes tortuosity [
4,
31].
Another finding of our study was the positive association between aneurysm neck size and tortuosity descriptors. Due to our knowledge, none of the previous researchers found such a correlation. A wider aneurysm neck among patients with tortuous BA could be another indication of substantial arterial wall weakening due to the above-mentioned mechanisms. Also, the study of Qiu et al showed that aneurysm neck size is significantly associated with lower WSS [
37], which further explains that correlation.
Our study has some limitations. First, our control group included patients with aneurysm in a different location other than BA, due to the fact that patients without intracranial aneurysm rarely undergo DSA. Another limitation was our inability to measure BA tortuosity before aneurysm formation; therefore, it remains unclear how aneurysm presence affects artery remodelling. Also, as BA is a rare location of aneurysm, our study group included only 71 patients with such aneurysms. Despite those limitations, we were able to precisely and objectively measure tortuosity of BA and show its association with risk of aneurysm formation.
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