thecal sac compression symptomsanterior thecal sac compressionventral thecal sac compressionmild thecal sac compressionthecal sac compression cervical spinedisc bulge compressing thecal sacthecal sac impressionflattening of the thecal sacthecal sac impingement symptomsthecal sac narrowingspine thecal sacdural sac compression
