Abstract
Since the initial publication of the International Study of Unruptured Intracranial Aneurysms (ISUIA), management of unruptured intracranial aneurysms has been mainly based on the size of the aneurysm. The contribution of morphological characteristics to treatment decisions of unruptured aneurysms has not been well studied in a systematic and location specific manner. We present a large sample of basilar artery tip aneurysms (BTA) that were assessed using a diverse array of morphological variables to determine the parameters associated with ruptured aneurysms. Demographic and clinical risk factors of aneurysm rupture were obtained from chart review. CT angiograms (CTA) were evaluated with Slicer, an open source visualization and image analysis software, to generate 3-D models of the aneurysms and surrounding vascular architecture. Morphological parameters examined in each model included aneurysm volume, aspect ratio, size ratio, aneurysm angle, basilar vessel angle, basilar flow angle, and vessel to vessel angles. Univariate and multivariate analyses were performed to determine statistical significance. From 2008–2013, 54 patients with BTA aneurysms were evaluated in a single institution, and CTAs from 33 patients (15 ruptured, 18 unruptured) were available and analyzed. Aneurysms that underwent reoperation, that were associated with arteriovenous malformations, or that lacked preoperative CTA were excluded. Multivariate logistic regression revealed that a larger angle between the posterior cerebral arteries (P1-P1 angle, p = 0.037) was most strongly associated with aneurysm rupture after adjusting for other morphological variables. In this location specific study of BTA aneurysms, the larger the angle formed between posterior cerebral arteries was found to be a new morphological parameter significantly associated with ruptured BTA aneurysms. This is a physically intuitive parameter that can be measured easily and readily applied in the clinical setting.
Highlights
Because of the availability of imaging, it has been been determined that nearly 3% of the population has an unruptured intracranial aneurysm. [1,2] Since the completion of the International Study of Unruptured Intracranial Aneurysms (ISUIA), the management of unruptured intracranial aneurysms has been mainly based on the size of the aneurysm. [3,4,5,6,7] with the recent publication of the large, prospective Unruptured Cerebral Aneurysm Study (UCAS) of Japan there has been mounting evidence for the importance of size, and of the location and morphology of the aneurysm in predicting rupture risk
Definition of morphological parameters We examined well-studied parameters of aneurysm morphology that have been utilized in the study of aneurysms of other subtypes including aneurysm size, volume, aspect ratio, aneurysm angle, vessel angles, size ratio, flow angles, and vessel to vessel angles. [9,19,20,21] We defined several novel parameters that were specific to the unique anatomy of basilar tip aneurysms (BTA) including posterior cerebral artery to posterior cerebral artery angle (P1-P1 angle), superior cerebellar artery to superior cerebellar artery angle (SCASCA angle). (Figures 1 and 2) Aneurysm maximum height is measured as the largest cross-sectional diameter of the aneurysm measured from the base of the aneurysm. [19,22,23] The maximum perpendicular height was the height of the aneurysm determined from the mid-point of the base to the dome
Ruptured BTAs were nearly significantly associated with larger basilar vessel angles and were significantly associated with larger P1-P1 angles in a relationship that was preserved in multivariate analysis
Summary
Because of the availability of imaging, it has been been determined that nearly 3% of the population has an unruptured intracranial aneurysm. [1,2] Since the completion of the International Study of Unruptured Intracranial Aneurysms (ISUIA), the management of unruptured intracranial aneurysms has been mainly based on the size of the aneurysm. [3,4,5,6,7] with the recent publication of the large, prospective Unruptured Cerebral Aneurysm Study (UCAS) of Japan there has been mounting evidence for the importance of size, and of the location and morphology of the aneurysm in predicting rupture risk. [8] There have been several recent aneurysm location specific studies of the contribution morphology to increased rupture risk and possible management decisions but none has addressed the morphological characteristics unique to basilar tip aneurysms (BTA) [9,10,11,12].Unruptured basilar tip aneurysms account for nearly 3% of all intracranial aneurysms. [1,13] The International Subarachnoid Aneurysm Trial (ISAT) demonstrated that the basilar apex location, in addition to size, was the strongest predictor of hemorrhage. [3,4,5,6,7] with the recent publication of the large, prospective Unruptured Cerebral Aneurysm Study (UCAS) of Japan there has been mounting evidence for the importance of size, and of the location and morphology of the aneurysm in predicting rupture risk. [8] There have been several recent aneurysm location specific studies of the contribution morphology to increased rupture risk and possible management decisions but none has addressed the morphological characteristics unique to basilar tip aneurysms (BTA) [9,10,11,12]. We present a large sample of basilar tip aneurysms that were assessed using a diverse array of morphological variables both intrinsic to the aneurysm and related to its surrounding vasculature to determine the parameters associated with rupture
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