Background: Chronic intracranial large vessel occlusion (LVO), resulting from progressive atherosclerosis or thrombosis, contributes significantly to ischemic strokes, 8-10% in North America and up to 50% in the Chinese population. This condition leads to cerebral hypoperfusion, brain ischemia, and potentially cognitive impairment. While extra-to-intracranial bypass surgery has shown limited benefit, recent advances in endovascular treatment (EVT) for acute ischemic stroke show promise. Preliminary reports suggest EVT may be feasible for chronic intracranial artery occlusions. Still, outcomes vary and perioperative risks remain high, particularly for intradural occlusions, which are technically more challenging and less studied.

Objectives: This study aims to evaluate the feasibility, safety, and clinical outcomes of EVT for symptomatic chronic intradural large vessel occlusions. Primary endpoints include technical success, complication rates, and functional outcomes, as measured by the modified Rankin Scale (mRS) at 3 months and the last follow-up. Safety endpoints include mortality, ischemic stroke, and periprocedural complications.

Design: A multicenter, retrospective and prospective observational study involving 10-20 experienced centers worldwide. Data from approximately 40-80 patients treated between January 2020 and December 2024 will be collected by local neuroradiologists, neurologists, or neurosurgeons. Clinical data (demographics, comorbidities, symptoms, outcomes), imaging data (pre-, post-, and follow-up), procedural details, and medication regimens will be collected. Inclusion criteria target adult patients with symptomatic chronic intradural occlusions of key intracranial arteries (ICA, MCA, VA, BA). Symptomatic occlusion is defined by neurological deficits or imaging evidence of ischemia. The data analysis will be performed by the local team at the Inselspital, Bern, Switzerland.

Aim: To descriptively analyze patient characteristics, treatment approaches, complications, and hemodynamic changes post-EVT to inform future therapeutic strategies for this challenging condition.

Inclusion Criteria:

• all consecutive patients who undergone endovascular recanalization for chronic intradural large vessel occlusions between January 1st, 2020, and December 31st, 2024 involving the following locations: internal carotid artery (ICA), middle cerebral artery (MCA), vertebral artery (VA), and basilar artery (BA)

Exclusion Criteria:

• presence of documented written or verbal refusal

The intradural occlusion is defined as the occlusion entirely located or extended into an intradural vascular segment (e.g., ICA occlusion extending from the extradural ICA to the ophthalmic ICA segment).

The ICA segments are defined as follows:

• Extradural ICA segment - from the ICA origin until the distal dural ring
• Ophthalmic ICA segment - from the distal dural ring right below the origin of the posterior communicating artery (PCOM)
• Communicating ICA segment - right from the PCOM origin to the ICA termination (bifurcation)

The symptomatic occlusion is defined as acute neurological impairment and/or acute ischemic stroke or hypoperfusion within the affected vascular territory detected on baseline imaging.