Table 5.

Comparison of hemodynamic and hydrodynamic parameter according to the type of surgery. All results are expressed as a percentage change. This is calculated as the ratio between the preoperative and postoperative values. A change of less than 100% indicates a decrease. A value greater than 100% indicates an increase. SVaqu: stroke volume of CSF in Sylvius aqueduct, SVforamen: stroke volume of CSF at the foramen magnum level, SVtonsils: stroke volume of tonsils (it is analyzed by a semi-automatic segmentation of the tonsils according to the same method as the CSF, this allows a quantification of the pulsatility of the tonsils during a cardiac cycle), SVcerv: stroke volume of CSF at cervical level, SVvasc: stroke volume of arteriovenous system, AMPvenous: amplitude of venous flow curve, SVsyrinx: stroke volume into the syringomyelia.

Variations in the Measurement of the Parameters Studied before and after Surgery (%)	Extradural Approach	Duraplasty	p
SVaqu	101 ± 24	71 ± 35	0.21
SVcerv	145 ± 99	106 ± 46	0.59
SVforamen	399 ± 236	453 ± 330	0.43
SVtonsils	35 ± 59	48 ± 55	0.52
SVvasc	89 ± 22	95 ± 29	0.26
AMPvenous	105 ± 18	97 ± 52	0.78
Correction factor	86 ± 11	65 ± 27	0.36
SVsyrinx	25 ± 35	20 ± 30	0.70