Vessel wall enhancement of intracranial aneurysms: fact or artifact?

Abstract

<jats:sec><jats:title>OBJECTIVE</jats:title><jats:p>For patients with subarachnoid hemorrhage (SAH) and multiple intracranial aneurysms, it is often challenging to identify the ruptured aneurysm. Some investigators have asserted that vessel wall imaging (VWI) can be used to identify the ruptured aneurysm since wall enhancement after contrast agent injection is presumably related to inflammation in unstable and ruptured aneurysms. The aim of this study was to determine whether additional factors contribute to aneurysm wall enhancement by assessing imaging data in a series of patients.</jats:p></jats:sec><jats:sec><jats:title>METHODS</jats:title><jats:p>Patients with symptoms of SAH who subsequently underwent VWI in the period between January 2017 and September 2018 were eligible for study inclusion. Three-dimensional turbo spin-echo sequences with motion-sensitized driven-equilibrium preparation pulses were acquired using a 3-T MRI scanner to visualize the aneurysm wall. Identification of the ruptured aneurysm was based on aneurysm characteristics and hemorrhage distributions on MRI. Complementary imaging data (CT, DSA, MRI) were used to assess potential underlying enhancement mechanisms. Additionally, aneurysm luminal diameter measurements on MRA were compared with those on contrast-enhanced VWI to assess the intraluminal contribution to aneurysm enhancement.</jats:p></jats:sec><jats:sec><jats:title>RESULTS</jats:title><jats:p>Six patients with 14 aneurysms were included in this series. The mean aneurysm size was 5.8 mm (range 1.1–16.9 mm). A total of 10 aneurysms showed enhancement on VWI; 5 ruptured aneurysms showed enhancement, and 1 unruptured but symptomatic aneurysm showed enhancement on VWI and ruptured 1 day later. Four unruptured aneurysms showed enhancement. In 6 (60%) of the 10 enhanced aneurysms, intraluminal diameters appeared notably smaller (≥ 0.8 mm smaller) on contrast-enhanced VWI compared to their appearance on multiple overlapping thin slab acquisition time of flight (MOTSA-TOF) MRA and/or precontrast VWI, suggesting that enhancement was at least partially in the aneurysm lumen itself.</jats:p></jats:sec><jats:sec><jats:title>CONCLUSIONS</jats:title><jats:p>Several factors other than the hypothesized inflammatory response contribute to aneurysm wall enhancement. In 60% of the cases in this study, enhancement was at least partially caused by slow intraaneurysmal flow, leading to pseudo-enhancement of the aneurysm wall. Notwithstanding, there seems to be clinical value in differentiating ruptured from unruptured aneurysms using VWI, but the hypothesis that we image the inflammatory cell infiltration in the aneurysm wall is not yet confirmed.</jats:p></jats:sec>

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

“…Cornelissen et al assumed that wall enhancement is not causally linked with inflammatory processes but rather attributable to method-inherent failure of blood signal suppression in low-flow conditions [ 40 , 41 ]. The results of our study suggest that inflammatory changes probably add to the extent of wall enhancement, and that even without convincing proof of a causal link, wall enhancement indicates the presence of a hemodynamic environment promoting inflammatory and degenerative processes and might therefore still serve as a surrogate marker for aneurysm wall instability.…”

Regional Aneurysm Wall Enhancement is Affected by Local Hemodynamics: A 7T MRI Study

“…21 However, several factors other than inflammation have been proposed as potential causes of increased AWE signals, in particular low-flow patterns that lead to pseudoenhancement signals in vivo. 22 Our purpose was to further investigate possible associations between local flow characteristics and focal AWE with the hope of shedding light on the mechanisms responsible for wall enhancement. We used high-resolution 7T MR imaging in determining AWE and studied the local flow patterns in different areas of the aneurysm.…”

Significance of aneurysm wall enhancement on high-resolution vessel wall magnetic resonance imaging in clinical management of patients with intracranial aneurysms

“…However, the most promising clinical application of HR-VW MRI in patients with intracranial aneurysms is the identification of aneurysms which are at greater risk of rupture. In our view, radiologists and referring clinicians should be aware of several issues before incorporating this imaging tool into daily clinical practice [33,34]. Firstly, we do not really know if the enhancement we see on HR-VW MRI, either circumferential or focal, at the aneurysm periphery is indeed within its wall.…”