[1] Univ Pittsburgh, Dept Surg, Med Ctr, Pittsburgh, PA 15213 USA
[2] Univ Virginia, Sch Med, Charlottesville, VA 22908 USA
[3] El Bosque Univ, Dept Neurosci & Neurosurg, Bogota, Colombia
[4] South Colombian Univ, Sch Med, Neiva, Colombia
[5] North Hampshire Hosp, Dept Surg, Basingstoke, Hants, England
[6] Valle Univ, Dept Surg, Cali, Colombia
[7] Angeles Lomas Hosp, Dept Surg, Mexico City, DF, Mexico