Fig. 5

a Classification of foraminal stenosis on sagittal T2-WI starting from normal findings (Left) to stenosis (Right): normal width of the foramina; slight stenosis; moderate stenosis; severe stenosis. b Classification of spinal canal stenosis on axial  T2-WI starting from normal findings to stenosis. From Left to Right: Grade 0, normal width of the spinal canal, no stenosis; Grade 1, slight stenosis, without significant aggregation of the nerve roots (the reduction in size of the canal is due to bilateral hypertrophy of the ligamentum flavum—red arrow; a bilateral facet fluid joint collection is also associated—blue arrow); Grade 2, moderate stenosis (bilateral hypertrophy of the ligamentum flavum—red arrow. Nerves of cauda equina are aggregated, but cerebrospinal fluid—CSF—is still evident); Grade 3, severe stenosis (entire cauda equina appears as a bundle due to all degenerative processes’ compression, but posterior epidural fat is still visible); Grade 4, extreme severe stenosis (no rootlets and posterior epidural fat are visible)