Multimodal validation of focal enhancement in intracranial aneurysms as a surrogate marker for aneurysm instability

Abstract

Purpose Circumferential enhancement on MR vessel wall imaging has been proposed as a biomarker of a higher risk of rupture in intracranial aneurysms. Focal enhancement is frequently encountered in unruptured aneurysms, but its implication for risk stratification and patient management remains unclear. This study investigates the association of focal wall enhancement with hemodynamic and morphological risk factors and histologic markers of wall inflammation and degeneration. Methods Patients with an unruptured middle cerebral artery aneurysm who underwent 3D rotational angiography and 3T MR vessel wall imaging showing focal wall enhancement were included. Hemodynamic parameters were calculated based on flow simulations and compared between enhanced regions and the entire aneurysm surface. Morphological parameters were semiautomatically extracted and quantitatively associated with wall enhancement. Histological analysis included detection of vasa vasorum, CD34, and myeloperoxidase staining in a subset of patients. Results Twenty-two aneurysms were analyzed. Enhanced regions were significantly associated with lower AWSS, lower maxOSI, and increased LSA. In multivariate analysis, higher ellipticity index was an independent predictor of wall enhancement. Histologic signs of inflammation and degeneration and higher PHASES score were significantly associated with focal enhancement. Conclusion Focal wall enhancement is colocalized with hemodynamic factors that have been related to a higher rupture risk. It is correlated with morphological factors linked to rupture risk, higher PHASES score, and histologic markers of wall destabilization. The results support the hypothesis that focal enhancement could serve as a surrogate marker for aneurysm instability.

High-Resolution Vessel Wall Magnetic Resonance Imaging of Small Unruptured Intracranial Aneurysms

“…However, we encountered both types of AWE when evaluating the images ( Figure 3 ). Several studies have investigated the relationship between focal AWE and specific hemodynamic factors [ 26 , 27 , 28 ]. The results of these studies revealed that focal AWE occurs at the location of lower wall shear stress, a hemodynamic condition that may be related to a higher risk of aneurysm rupture.…”

“…In their recent paper, Cebral et al reported that low wall shear stress is associated with atherosclerotic and hyperplastic changes in the aneurysmal wall [ 29 ]. In one of the abovementioned studies, Larsen et al provided the results of the histopathological analysis from a subset of patients who underwent microsurgical aneurysm clipping [ 26 ]. The presence of histological inflammatory markers was significantly associated with a larger extent of AWE.…”

Pseudo‐Enhancement in Intracranial Aneurysms on Black‐Blood MRI: Effects of Flow Rate, Spatial Resolution, and Additional Flow Suppression

“…VWE has been linked to vessel‐wall inflammation and associated with a higher risk of rupture 19–22 . 3D T 1 ‐weighted TSE sequences are typically applied for imaging of the vessel wall because they can effectively suppress the signal from flowing blood, providing full brain coverage within an adequate examination time 15, 32 .…”

“…Specific hemodynamic conditions, including low wall shear stress (WSS) and low oscillatory shear index (OSI) in the aneurysm, have been associated with a higher risk of rupture 24 . They have been shown to colocalize with contrast‐enhanced wall segments on BB MRI 22 …”

Imaging Inflammation – From Whole Body Imaging to Cellular Resolution

“…Therefore, risk stratification of patients diagnosed with an unruptured intradural aneurysm is crucial, but optimal management remains controversial. Recently, wall enhancement in intracranial saccular aneurysms on MR vessel wall imaging has been associated with a higher risk for rupture ( 42 – 46 ) ( Figure 2 ). Experimental studies indicated that flow triggered inflammation in the vessel wall (specifically, macrophage invasion in the vessel wall) may cause formation and growth of intracranial aneurysms ( 47 – 52 ).…”