Protocols The rationale and design of the Giant Intracranial Aneurysm Registry: a retrospective and prospective study Julius Dengler 1 , Peter U. Heuschmann 2 , Matthias Endres 2,3 , Bernhard Meyer 4 , Veit Rohde 5 , Daniel A. Rufenacht 6 , and Peter Vajkoczy 1à , on behalf of the Giant Intracranial Aneurysm Study Group Aims and Hypothesis Giant intracranial aneurysms have a poor prognosis mainly due to their high risk of rupture. Because their incidence is low, clinical trial evidence for adequate treatment is lacking. The Giant Intracranial Aneur- ysm Registry is designed to document current treatment strategies in giant aneurysm care and to monitor the course of the disease over five-years. It aims to evaluate the hypoth- esis that all three possible branches of therapy (conservative/ endovascular/surgical) lead to equal rupture rates. Design The Giant Intracranial Aneurysm Registry is an inter- disciplinary multicenter observational study. Each center re- cruits patients diagnosed with a giant intracranial aneurysm both prospectively and retrospectively. Primary outcome will be the aneurysm rupture rate at five-years of follow-up. Study Outcome Patient enrollment has begun at 20 neuro- vascular centers throughout Germany, with 19 further centers applying for local ethics approval to take part in the study. The first nine months are designed as a pilot phase followed by the integration of study centers throughout the EU and the initiation of separate sub-studies. Discussion Giant intracranial aneurysms have often been ignored or marginalized due to their low incidence. The Giant Intracranial Aneurysm Registry aims to lead to a better under- standing of these complex lesions and to serve as a basis for the development of future clinical studies. Key words: cerebral revascularization, clipping, coiling, giant intracranial aneurysm, Giant Intracranial Aneurysm Registry, SAH Executive Summary Aim Giant intracranial aneurysms remain among the most challen- ging neurovascular lesions. They have a poor prognosis mainly due to their high risk of rupture. As their incidence is low, clinical trial evidence for adequate treatment strategies is lacking. The Giant Intracranial Aneurysm Registry is designed to document the current treatment strategies in giant aneur- ysm care and to monitor the course of the disease. It is expected to serve as a basis for the development of future clinical studies. Design The Giant Intracranial Aneurysm Registry is an interdisciplin- ary multicenter observational study. Each center recruits patients diagnosed with a giant intracranial aneurysm both prospectively and retrospectively. Past medical history, events leading to the diagnosis, clinical presentation at admission, radiological findings, therapeutic intervention, complications of therapy and outcomes will be documented using standar- dized criteria at different time points up to five-years after the initial diagnosis. The primary outcome will be the aneurysm rupture rate at five-years of follow-up. Study outcomes Patient enrolment has begun at 20 neurovascular centers throughout Germany, with 19 further centers applying for local ethics approval to take part in the study. The first nine- months are designed as a pilot phase, followed by final DOI: 10.1111/j.1747-4949.2011.00588.x Conflict of Interest: None declared. Correspondence: Peter Vajkoczy à , Department of Neurosurgery, Charite ´, Universitaetsmedizin Berlin, CVK, Augustenburger Platz 1, 13553 Berlin, Germany. E-mail: peter.vajkoczy@charite.de 1 Department of Neurosurgery, Charite ´, Universitaetsmedizin Berlin, CVK, Berlin, Germany 2 Center for Stroke Research, Charite ´, Universitaetsmedizin Berlin, CCM, Berlin, Germany 3 Department of Neurology, Charite ´, Universitaetsmedizin Berlin, CCM, Berlin, Germany 4 Department of Neurosurgery, Technical University of Munich, Munich, Germany 5 Department of Neurosurgery, Universitaetsmedizin Goettingen, Goettingen, Germany 6 Department of Neuroradiology, Klinikum Hirslanden, Zurich, Switzerland & 2011 The Authors. International Journal of Stroke & 2011 World Stroke Organization Vol 6, June 2011, 266–270 266