Assess the Penumbra System in the Treatment of Acute Stroke

Current therapies for acute stroke are limited to the intravenous administration of a intravenous (IV) recombinant human tissue plasminogen activator (rtPA) for thrombolysis of the affected cerebral arteries within 3-4.5 hours from symptom onset, and the use of intra-arterial (IA) endovascular mechanical clot retrieval devices within 8 hours from ictus, all of which have limitations as mono therapies. For example, IV rtPA may not be very efficacious in large vessel occlusion and the long term effects of mechanical thrombectomy devices on patient functional outcome is unknown. This is a randomized, concurrent controlled study to assess the safety and effectiveness of the Penumbra System as adjunctive therapy to IV rtPA in the acute intervention of acute ischemic stroke. Patients presenting with symptoms of acute ischemic stroke who have evidence of a large clot burden (clot length \> 8mm) in the anterior circulation will be assigned to either IV rtPA therapy alone (0.9mg/kg to a maximum of 90mg) or a combined IV rtPA therapy (0.9mg/kg to a maximum of 90mg) and intra-arterial (IA) adjunctive treatment with the Penumbra System. Each treated patient will be followed and assessed for 3 months after enrollment.