Pressure changes following constriction of the cauda equina. An experimental study in situ.

During routine autopsies in 11 cadavers, the intact dural sac, including its nerve roots, was circumferentially constricted by a clamp while the pressure under the clamp among the nerve roots was recorded simultaneously. The first sign of a pressure increase--the critical size--occurred at a cross-sectional area of the cauda equina of 77 +/- 13 mm2. To achieve a pressure increase of 50 mm Hg, the cross-sectional area of the cauda equina had to be further constricted at an average of 19 +/- 8%. The corresponding constriction needed to achieve a pressure of 100 mm Hg was 26 +/- 8%. The results indicated that constriction of the cauda equina to a size less than 75 mm2 probably will affect the normal function of the nerve roots of the cauda.