Intraoperative monitoring for tethered spinal cord syndrome.

Functions of the lower extremities and bowel and bladder must be monitored during releasing surgery for tethered spinal cord syndrome, because neural elements are embedded in lipoma or anomalous tissues. Evoked muscle action potentials of the external anal sphincter muscle, external urethral sphincter muscle, and lower extremity muscles can indicate promptly whether or not neural elements are involved before the surgeon releases or cuts the tissue for cord release. It is also important to monitor vesical pressure because of different types of innervation from the external urethral and anal sphincters, in spite of slow reaction times of vesical pressure elevation. Evoked muscle action potentials indicate only motor function; therefore, it is more appropriate to record evoked spinal cord potentials from the spinal cord above a lumbosacral operative field, because sensory function can also be monitored. Evoked muscle action potentials are an easy and extremely sensitive monitoring system; nevertheless, monitoring of vesical pressure and evoked spinal cord potentials should also be done to achieve optimum monitoring. For the past 5 years, 10 patients have undergone cord-release surgery with such a monitoring system, and the results indicate no exacerbating case.