The Schizas classification is used to categorize spinal canal stenoses[^1] into four different degrees of severity.

Classification

Grade	Characteristic	Stenosis Grade
A1	The nerve roots are dorsal and occupy less than half of the dural sac area.	No to mild stenosis
A2	The nerve roots are dorsal with contact to the dura in a horseshoe configuration.	No to mild stenosis
A3	The nerve roots are dorsal and occupy more than half of the dural sac area.	No to mild stenosis
A4	The nerve roots are central and occupy most of the dural sac area.	No to mild stenosis
B	The nerve roots occupy the entire dural sac area. CSF can still be distinguished between the nerve roots.	Moderate stenosis
C	The individual nerve roots can no longer be distinguished. The dural sac appears with a homogeneous gray signal without distinguishable CSF.	Severe stenosis
D	In addition to the lack of distinguishability of the nerve roots and the absence of a CSF signal, there is also no distinguishable epidural fat posteriorly.	Extreme stenosis

Figure