Arjen Lindenholz

13 General Introduction 1 Clinical consequence of intracranial vessel wall lesions For both 3T and 7T MRI platforms, a number of intracranial vessel wall MR imaging sequences are currently available that provide clear visibility of the vessel wall and its pathology. 13,15,19,21,22,26,29 In addition, several (pictorial) reviews have recently been published addressing the current and potential clinical capabilities of intracranial vessel wall imaging in a variety of vascular pathologies. 1-4 As a result, an increasing number of radiologists and non-radiology clinicians are interested in implementing intracranial vessel wall MR imaging in clinical practice. However, apart from aiding diagnosis of central nervous system vasculitis by assessing specific vessel wall enhancement patterns, clear advantages for clinical decision- making are currently lacking. 20 One important reason is that – contrary to the extracranial arteries – histopathological validation ( in vivo versus ex vivo ) of intracranial vessel wall MR findings is virtually impossible to perform due to the lack of pathological specimens from living patients. An alternative option, solely ex vivo validation studies, show promising results, but are limited. 30-32 Therefore, the true nature of vessel wall MRI findings and their prevalence among different ethnicities has not been completely determined yet. Several alternative, more indirect methods of deducing the nature of intracranial vessel wall MR lesions are available. By studying their association with other established cerebrovascular markers and imaging findings, an assumption can be made as to the exact nature of these (at least most) lesions. For instance, if the presence and number of lesions coincide with the presence (and extent) of cerebrovascular risk factors like smoking and hypertension, they will more likely be atherosclerotic plaques ( Chapter 5 ). Furthermore, this method may aid in determining to translate these MR findings in a clinical perspective. This same reasoning may apply for parenchymal damage: if the vessel wall lesions that we see are true atherosclerotic plaques and thereby indicative of a certain atherosclerotic burden, we would expect more ischemic damage in patients with a high lesion load ( Chapter 6 ). This would also provide insight into the clinical value of visualizing these intracranial vessel wall lesions on MRI. Alternatively, an assumption can be made as to the exact nature of these lesions by monitoring the behavior of vessel wall lesions over time. Pre- and posttreatment intracranial vessel wall MRI or follow-up examinations may provide additional information in the development of a vessel wall lesion or vessel wall status. For example, lesions that disappear during follow-up without treatment are more likely transient in nature or iatrogenic in case of previous treatment with mechanical thrombectomy ( Chapter 7 ).