The relationship between the duration of acute cauda equina compression and functional outcomes in a rat model

Study Design. Immunohistochemical and behavioral study using a rat model of acute cauda equina syndrome (CES). Objective. To determine the effect of duration of extradural cauda equina compression (CEC) on bladder, sensory, and motor functions. Summary of Background Data. Cauda equina syndrome is a devastating injury treated with surgical decompression. Controversy exists regarding the optimal timing of surgery. Animal models of CES have focused on motor recovery but have not evaluated pain behavior or bladder function. Methods. A 4-mm balloon-tipped Fogarty catheter was inserted between the fifth and sixth lumbar lamina into the dorsal epidural space and inflated to compress the nerve roots at the L5 level. Maximal inflation was maintained at a constant balloon pressure of 304 Kpa for 1 or 4 hours. The catheter was inserted but not inflated in sham animals. During a 4-week period, pain behavior, bladder function, and locomotor function were assessed. Postmortem bladders and the lesi n ite were collected for analysis. Results. Mechanical allodynia was 2-fold greater in 1-hour CEC rats than 4-hour CEC (P = 0.002) and sham-operated (P = 0.001) rats at 4 weeks after injury. Hind limb locomotor function was not different between groups at 4 weeks after injury. Both the 1-hour and 4-hour CEC group rats retained greater volumes of urine than the sham-operated rats throughout the 4-week period (P < 0.05). At 4 weeks, bladder weight and volume were 2-fold greater in the 4-hour CEC group than in the 1-hour CEC group (P = 0.006 and P = 0.01, respectively). Histology of the bladder wall revealed an overall thinning after 4-hour CEC. Histology of the lesion site revealed a greater overall severity of injury after 4-hour CEC than after 1-hour CEC (P = 0.04) and sham operation (P = 0.002). Conclusion. Our data suggest that recovery of motor function is less affected by the timing of decompression compared with bladder function and pain behavior. Early decompression preserved bladder function but was associated with allodynia.