Syringomyelia associated with Type I CMI: a 21 year retrospective study on 75 cases treated by foramen magnum decompression with a special emphasis on the value of tonsil resection - Guyotat,J.; Bret,P.; Jouanneau,E.; Ricci,A.C.; Lapras,C. (Acta Neurochir (Wien), 1998)