Arjen Lindenholz

172 CHAPTER 7 Discussion In the current study, we show the patterns of vessel wall changes that can be anticipated to be seen in diagnostic vessel wall MRI studies in patients with stroke after IAT with a thrombosuction device compared with patients with stroke in whomno thrombectomy is performed. MR vessel wall imaging, in the subacute and chronic stages after IAT, showed more foci of vessel wall enhancement on the side treated with thrombectomy, while no difference between ipsi- and contralateral enhancement was found in the patients with stroke without IAT. Additionally, in the IAT-group, these enhancing foci were more often concentric in the vessels ipsilateral to the thrombectomy site compared with the contralateral side. The higher number of ipsilateral foci of (concentric) contrast enhancement may be explained by several mechanisms: 1) the direct effect of the mechanical forces of the used thrombosuction device; 2) the indirect effect of the removed occluded thrombus by the release of (local) inflammatory molecules and 3) pre-existent atherosclerotic plaques with possible active inflammation. First, the direct effects of the mechanical forces of the thrombectomy procedure may induce vessel wall changes that cause vessel wall enhancement. This potential explanation is supported by previous imaging studies that studied the effect of IAT using a stent- retriever (and one also including patients treated with a thrombosuction device) on the vessel wall on 3T MRI. 10-13,24 The study that also included patients with a thrombosuction device showed that concentric vessel wall enhancement, which occurred in respectively 67% and 14% of the patients in the IAT-group ( n = 15) versus the non-IAT group ( n = 14), was associated with the number of attempts, type of device and more frequent hemorrhagic transformation of the ischemic infarct (mean interval treatment - MRI; 3.66 ± 1.52 days). 13 In another series (IAT-group n = 6 vs. non-IAT group n = 10), MR vessel wall imaging showed wall thickening in 83% versus 30% and contrast enhancement in 67% versus 20% of patients, respectively, (mean interval treatment - MRI; 3.44 ± 2.58 days). 11 Also, in a recent study more contrast-enhancing vessel wall areas were found in the post-thrombectomy group ( n = 6), scanned within 24 hours after treatment, compared with a control group ( n = 5). 12 In addition, some follow-up studies (ranging from several days up to two years) reported delayed arterial vessel wall abnormalities, postulating that these might be attributable to endothelial damage after IAT. 3,6,8,25,26 On the other hand, in a study with 23 stroke patients who were scanned within one week after thrombectomy, major vessel wall damage such as disruption and stenosis were rare. 10 We limited our study to patients treated with a thrombosuction device. In this study 7T MRI was used, but previous 3T MRI and 7T MRI comparison studies