INTRODUCTION Intracranial aneurysms (IAs) are relatively common life-threatening diseases with a prevalence of 3%-5% in adults¹. Several imaging markers for unruptured IAs instability have been explored and aneurysm wall enhancement (AWE) as identified by contrast-enhanced vessel wall MRI (VW-MRI) has also been reported as a marker of unstable IAs². Another potential novel imaging marker of aneurysm vulnerability is irregular pulsation detected by four-dimensional computed tomography angiography (4D-CTA), which may represent a focal weakening of the aneurysm wall³. Current studies found atherosclerotic proteins might have a pivotal effect on the inflammation and remodeling of aneurysm wall⁴. But the association between AWE and irregular pulsation and the effect of atherosclerotic proteins on the two risk factors is still unknown and our study aims to investigate this open question.
METHODS This retrospective study included consecutive patients with IAs who underwent 4D-CTA and VW-MRI between January 2018 to July 2022. The values of serum Lp(a) (Lipoprotein[a]), HDL (high-density lipoprotein), LDL (low-density lipoprotein), and total cholesterol levels within 30 days of diagnosis were collected. 4D-CTA was performed on a 320-detector row CT scanner (Aquilion ONE VISION, Canon Medical System Corporation, Otawara, Japan). Vessel wall MRI was performed on a 3.0T MR scanner (Prisma, Siemens Healthcare or Ingenia, Philips Healthcare or Prisma). The imaging protocols for MR scanning on Ingenia and Prisma were as follows respectively: 1) T1WI volume isotropic turbo spin-echo acquisition (T1-VISTA) sequence with following parameters: TR/TE 800/20msec, number of slices 80, field of view 250mm×162mm, voxel size 0.6mm×0.6mm×0.6mm, acquisition matrix 416×269, and scan time 5 minutes 2 seconds. 2) T1-weighted 3D black-blood fast spin echo with variable flip angle trains (SPACE) sequence with following parameters: TR/TE 1000/15msec, number of slices 240, field of view 193mm× 193mm, voxel size 0.6mm× 0.6mm× 0.6 mm, acquisition matrix 320× 320, and scan time 9 minutes 13 seconds. Post-contrast VW-MRI sequence was acquired 5 minutes after Gadolinium-based contrast agent (Magnevist, Bayer Healthcare, Berlin, German) injection (with a dose of 0.1 mmol/kg, at a rate of 1.5ml/s). Geometric and morphologic parameters were measured and the presence of irregular pulsation (defined as a temporary focal protuberance ≥1 mm on more than three successive frames) was identified on 4D-CTA movies6. AWE was estimated on VW-MRI and classified as 4 grades (grade 0 for none or questionable focal trace enhancement, grade 1 for focal thick [<1mm] enhancement, grade 2 for thin [maximum thickness, ≤1 mm] circumferential wall enhancement, or grade 3 for thick [maximum thickness, ≥1 mm] circumferential wall enhancement)7. The association between atherosclerotic proteins and AWE and irregular pulsation was analyzed. RESULTS One hundred and thirty-one patients with 131 saccular IAs were included in this study. Irregular pulsation was observed in 38.2% (50/131) of IAs. Among 131 aneurysms, 63 (48.1%) were enhancing; 21(16.0%) were grade 1, 18 (13.7%) were grade 2, and 24 (18.3%) were grade 3. There was a significantly strong correlation between AWE and irregular pulsation (phi coefficient=0.537, p<0.001). IAs with irregular pulsation showed much higher levels of Lp(a) compared with those without irregular pulsation (median [interquartile range], 135.6 [43.5–328.9] versus 74.2 [35.9–171.0], P=0.029). similarly, IAs with enhacement showed much higher levels of Lp(a) compared with those without enhancemnet (median [interquartile range], 137.3 [44.6–322.9] versus 69.2 [25.5–137.4], P=0.001).
DISCUSSION Recent studies have showed both AWE and irregular pulsation were promising for identification of unstable aneurysms. This study demonstrated a strong positive correlation between Lp(a) and AWE and irregular pulsation. Lp(a) was reported to have possible proatherogenic and proinflammatory functions in the arterial wall⁵, which might explain its association with AWE. Persistent inflammation of aneurysm wall involves increased elastic lamina breakdown and may thereby cause focal weakening of the wall, perhaps explaining the formation of irregular pulsation. Further research is still needed, however, to study the association between Lp(a) and irregular pulsation and AWE. CONCLUSION Higher levels of Lp(a) were significantly associated with increased wall enhancement and irregular pulsation. A larger study is needed to confirm these findings.

Acknowledgements

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