Evaluation of laser- and radiofrequency-generated dorsal root entry zone lesions in the cat

The current study was designed to measure and compare the size of dorsal root entry zone lesions made in the midthoracic spinal cord of anesthetized cats with a carbon dioxide laser and the radiofrequency (RF) probe utilizing currently employed clinical parameters. Cats were monitored intraoperatively with somatosensory evoked potentials (SSEPs) derived from stimulation of the ipsilateral posterior tibial nerve in order to assess the acute effect of lesion production on function within the ipsilateral dorsal column. Daily postoperative neurologic evaluations were recorded. The lesioned segments of spinal cord from sacrificed animals were examined histologically to determine the extent of cord injury at 1 and 30 days. SSEPs remained normal for the laser group, but were uniformly attenuated or lost in the RF group. Neurologically, the laser group fared better, with only a mild transient monoparesis, compared to a persistent moderate paraparesis for the RF group. On histologic examination, the depths of the laser and electrode lesions were similar, but the RF lesions showed more lateral spread. Laser lesions comprised 4.4 +/- 1.6% of the cross-sectional area of the spinal cord whereas the RF lesions occupied 22.8 +/- 4%. These findings demonstrate that at the parameters employed, the carbon dioxide laser produces smaller lesions than does the RF electrode.