TABLE 1:

Grading system for lateral recess root compression

Grade	Myelography	CT Myelography or MR Imaging
0	Normal	Normal
1	Reduced contrast material within the lateral recess, indentation on the dural sac, nerve root is normal and unaffected	Reduced size of the corner of the lateral canal or recess; trefoil shape to the lateral recess, either congenital or acquired; early acute angular narrowing of the corner of the canal and thecal sac; nerve root is visualized and not widened, flattened, or altered
2	Reduced contrast material within the lateral recess (not obliterated); indentation on the dural sac; nerve root is flattened, widened, or laterally pinched and medially displaced due to canal corner changes	Reduced size of the corner of the lateral canal or lateral recess, trefoil shape and narrowing of the lateral recess, angular pinch-like shape and narrowing of the lateral canal and thecal sac, nerve root judged compressed in the small trefoil recess or angled pinch but recess judged not totally obliterated, nerve root may be deviated medially
3	Complete obliteration of contrast material from the lateral recess or corner of the canal; thumbprint-like obliteration of contrast material in the lateral recess; severe lateral pinch of the corner of the canal with obliteration of contrast material at the lateral margin; nerve root is trapped in the thumbprint compression, widened-flattened on the thumbprint, displaced medially and widened and flattened laterally due to lateral canal corner changes	Severe facet hypertrophy and disc/end plate changes, no CSF or space identified in the lateral recess or corner of the canal, severe angular pinch of the lateral corner of the canal, root may or may not be clearly visible, root may be seen coursing through the compressed lateral recess, root may be seen as medially displaced