Recent years have witnessed a change in the therapeutic paradigm of stroke with the advent of mechanical thrombectomy as the reference treatment.

However, despite the achievement of effective proximal recanalization in nearly 80% of patients, nearly half of these patients have an unfavorable functional outcome. Several causes can be mentioned, such as the extent of the initial ischemic damage, the occurrence of complications related to reperfusion treatments or the occurrence of thrombosis of the downstream microvascularization. The latter is a phenomenon that has been known and studied increasingly over the last twenty years. It is the result of multiple cellular remodeling following ischemia and at the origin of an endoluminal filling by platelets, inflammatory cells and fibrin. This phenomenon introduces the fundamental difference between recanalization, i.e. the removal of the obstruction by the thrombus, and reperfusion, which translates into a satisfactory supply of oxygen to the ischemic tissues and therefore the expected result of these treatments. However, not all recanalization is necessarily accompanied by reperfusion, which is the phenomenon of no-reflow. This last situation could be explained by downstream microvascular thrombosis. Studies have shown the interest of intravenous thrombolysis associated with mechanical thrombectomy to preserve this vascular bed and improve cerebral reperfusion. More recently, a study has also shown the value of adding intra-arterial thrombolysis after mechanical thrombectomy. Nevertheless, there is currently no clinical evidence of the reality and prognostic importance of downstream microvascular thrombosis.

Advances in imaging have allowed the development of susceptibility weighted imaging (SWI) sequences with millimeter resolution, allowing a precise study of vascular damage and the appearance of previously unseen remodeling. Among them, the existence of cortical or juxta-cortical microinfarcts whose remnographic characteristics differed by the presence of a SWI hyposignal. The hypothesis evoked is that of a hemorrhagic remodeling consecutive to the barrier rupture. However, in view of the pathophysiology explained so far and the hypointense character of the thrombi on the SWI sequences, these remodeling could in fact be not microbleeding but rather markers of thrombosis in the downstream microcirculation. MRI would allow to identify the presence and the importance of microvascular thrombosis and thus to bring arguments to specifically target this microvascular component, consequence of cerebral ischemia, by antithrombotic or thrombolytic treatments.

The objective of our project is therefore to carry out a study focused on a better description and understanding of cortical and basal ganglia SWI hyposignals with a histopathological correlation and with the clinical prognosis.

Inclusion Criteria:

• Age >18 years
• Managed for sylvian ischemic stroke
• Requiring brain MRI as part of the evaluation for possible decompressive hemicraniectomy (DH).

Or

• Having undergone a post-thrombectomy brain scan showing cortical hyperdensities and indication for a possible decompressive hemicraniectomy
• Consent to participate in the study
• Affiliated or beneficiary of a health insurance plan

Exclusion Criteria:

• Absolute or relative contraindication to gadobutrol injection (history of true allergic reaction or intolerance to gadobutrol, renal insufficiency with creatinine clearance <15ml/min). In particular, if an allergic reaction was observed during the injection of gadobutrol performed for care during the acute phase MRI a few hours or days before.
• Patient benefiting from a legal protection measure
• Pregnant or breastfeeding woman