[1] UNIV HOSP UPPSALA,DEPT NEUROSURG,S-75185 UPPSALA,SWEDEN
[2] HUDDINGE HOSP,DEPT ORTHOPAED SURG,S-14186 HUDDINGE,SWEDEN
[3] KAROLINSKA HOSP,DEPT NEUROSURG,S-10401 STOCKHOLM 60,SWEDEN
[4] KAROLINSKA INST,ST GORANS CHILDRENS HOSP,DEPT PSYCHIAT,S-11281 STOCKHOLM,SWEDEN