[1] Univ Texas Southwestern Med Ctr Dallas, Dept Neurol Surg, Dallas, TX USA
[2] Univ Texas Hlth Sci Ctr Houston, McGovern Med Sch, Houston, TX USA
[3] Michigan State Univ, Coll Human Med, E Lansing, MI USA
[4] Univ Penn, Sch Med, Philadelphia, PA 19104 USA
[5] Childrens Hlth, Ctr Cerebrovasc Dis Children, Dallas, TX USA
[6] Univ Penn, Sch Med, 3400 Civ Ctr Blvd, Philadelphia, PA 19104 USA