RT Journal Article SR Electronic T1 Sentinel Headache: A Warning Sign Preceding Every Fourth Aneurysmal Subarachnoid Hemorrhage JF American Journal of Neuroradiology JO Am. J. Neuroradiol. FD American Society of Neuroradiology DO 10.3174/ajnr.A4467 A1 H. Joswig A1 J.Y. Fournier A1 G. Hildebrandt A1 M.N. Stienen YR 2015 UL http://www.ajnr.org/content/early/2015/07/16/ajnr.A4467.abstract AB