Fig. 2

Schizas classification: (a) Grade A1: the rootlets lie dorsally and occupy less than half of the dural sac area; (b) Grade A2: the rootlets lie dorsally, in contact with the dura but in a horseshoe configuration; (c) Grade A3: the rootlets lie dorsally and occupy more than half of the dural sac area; (d) Grade A4: the rootlets lie centrally and occupy the majority of thedural sac area; (e) Grade B: the rootlets occupy the whole of the dural sac, but they can still be individualized; (f) Grade C: no rootlets can be recognized, here is epidural fat present posteriorly; (g) Grade D: in addition to no rootlets being recognizable there is no epidural fat posteriorly