MR imaging of intracranial vessel wall pathologies and parenchymal brain damage

Abstract

The probable cause of ischemic stroke is often inferred from the size and location of the infarct, in combination with an evaluation of the heart and the presence of extracranial arterial occlusion or high-grade stenosis. The used conventional imaging techniques were designed to image the intracranial vessel lumen instead of the wall itself. Pathological changes, however, often (primarily) involve the vessel wall, even without causing luminal stenosis. Therefore, conventional imaging techniques generally underestimate the true disease burden. To image the vessel wall directly, intracranial vessel wall MRI can be used. This quickly evolving imaging technique receives more and more attention both in the clinical and the scientific setting. In this thesis, the utility of intracranial vessel wall MRI in two different cerebrovascular diseases: intracranial atherosclerosis and cerebral vasculitis is described. Focussing on the combined depiction of intracranial vessel wall pathologies and parenchymal brain damage, Chapter 3 demonstrates that the combination of infarcts and vessel wall lesions can help to differentiate between different disease entities. For instance, patients with intracranial atherosclerosis show a high prevalence of brain parenchymal lesions (both CMIs and macroinfarcts), and macroinfarcts seem to be related to specific pattern of vessel wall abnormalities (Chapter 4). For the assessment of intracranial atherosclerosis a transverse large coverage MR brain sequence seems to be most promising for clinical purposes (Chapter 5). This sequence was successfully used in patients with middle cerebral artery stenosis, demonstrating that many asymptomatic lesions can be observed next to the known symptomatic lesion(s) (Chapter 6). Finally, Chapter 7 sheds light on the use of vessel wall imaging in cerebral vasculitis. The diagnosis of this disease is very challenging and includes invasive methods in the diagnostic work-up, with a brain biopsy being the gold standard. Sensitivities of conventional methods, however, are low, necessitating a different, less invasive method, like vessel wall imaging. In this final chapter, intracranial vessel wall MRI in patients suspected of vasculitis demonstrates resolution of contrast enhancement of vessel wall lesions after therapy, suggesting that visualizing the enhancement pattern of the (pathological) vessel wall could be a first step towards a non-invasive diagnostic tool to diagnose these patients. The sequence can be easily implemented in the clinical protocol and used for diagnosis, since both 3T and 7T were equally able to image the enhancement pattern. This provides us with a new potential application of intracranial vessel wall in clinical practice.