Rationale: Recently our study group reported the results of the Basilar Artery International Cooperation Study (BASICS), a prospective registry of patients with an acute symptomatic basilar artery occlusion (BAO). Our observations in the BASICS registry underscore that we continue to lack a proven treatment modality for patients with an acute BAO and that current clinical practice varies widely. Furthermore, the often-held assumption that intra-arterial thrombolysis (IAT) is superior to intravenous thrombolysis (IVT) in patients with an acute symptomatic BAO is challenged by our data. The BASICS registry was observational and has all the limitations of a non-randomised study. Interpretation of results is hampered by the lack of a standard treatment protocol for all patients who entered the study.

Objective: Evaluate the efficacy and safety of IAT in addition to best medical management (BMM) in patients with basilar artery occlusion.

Study design: Randomised, multi-centre, open label, controlled phase III, treatment trial.

Study population: Patients, aged 18 years and older, with CTA or MRA confirmed basilar occlusion.

Intervention: Patients will be randomised between BMM with additional IAT versus BMM alone. IAT has to be initiated within 6 hours from estimated time of BAO. If treated with as part of BMM, IVT should be started within 4.5 hours of estimated time of BAO.

Main study parameters/endpoints: Favorable outcome at day 90 defined as a modified Rankin Score (mRS - functional scale) of 0-3.

Inclusion criteria

• Symptoms and signs compatible with ischemia in the basilar artery territory.
• Basilar artery occlusion (BAO) confirmed by CTA or MRA.
• Age 18 years or older (i.e., candidates must have had their 18th birthday).
• If IVT is considered as part of best medical management, IVT should be started within 4.5 hours of estimated time of BAO. (Estimated time of BAO is defined as time of onset of acute symptoms leading to clinical diagnosis of BAO or if not known last time patient was seen normal prior to onset of these symptoms).
• Initiation of IAT should be feasible within 6 hours of estimated time of BAO.

Exclusion criteria

• Pre-existing dependency with mRankin ≥3.
• Females of childbearing potential who are known to be pregnant and/or lactating or who have positive pregnancy tests on admission.
• Patients who require hemodialysis or peritoneal dialysis.
• Other serious, advanced, or terminal illness.
• Any other condition that the investigator feels would pose a significant hazard to the patient if thrombolytic therapy is initiated.
• Current participation in another research drug treatment protocol (patient cannot start another experimental agent until after 90 days).
• Informed consent is not or cannot be obtained.

Imaging exclusion criteria

• High-density lesion consistent with hemorrhage of any degree.
• Significant cerebellar mass effect or acute hydrocephalus.
• Bilateral extended brainstem ischemia.