Discrepancy between intraoperative SSEP's and postoperative function

Abstract

The authors report a case in which midline myelotomy for the removal of a C4-T4 ependymoma was immediately followed by abolition of short-latency somatosensory evoked potentials (SSEP's) in response to bilateral posterior tibial nerve (PTN) stimulation which proved irreversible intraoperatively. Subsequent intraoperative testing also revealed obliteration of median nerve (MN)-elicited responses. Postoperatively, joint and vibration sensations deteriorated in the lower extremities and there was unchanged very mild impairment of light touch, pinprick, and temperature sensibilities without significant loss of muscle strength. Nearly 5 months after surgery, despite recovery of postural and vibratory senses in the lower limbs and of SSEP's in response to MN stimulation, no SSEP's could be demonstrated on PTN stimulation. The possibility of "false positive" results (that is, intraoperative SSEP abolition without postoperative motor deficits) and of dissociations between SSEP's and deep sensation should be taken into consideration when interpreting SSEP's intraoperatively.

Reliability of perioperative SSEP recordings in spine surgery

“…Owing to the sensitivity and specificity of SSEP monitoring, the incidence of postoperative paraplegia can be significantly reduced. 3,[7][8][9][10] However, a reliable intraoperative monitoring demands appropriate procedures of anesthesia, since the anesthetic itself, as well as accompanying hypothermia and hypotension, have a serious influence on evoked potentials. The depressant effect of volatile anesthetics on evoked potentials is well known.…”

26 Electrophysiological Monitoring

“…Overall, the rate of false-positive results with the use of SSEP monitoring averages 2%, with a reported range of 0 to 7%. [24][25][26][27] In 1992, the SRS issued a position statement advocating SSEP monitoring as the standard of care for scoliosis surgery. 28 A recent survey of 37 members of the Spinal Deformity Study Group of the SRS revealed that the mode of neuromonitoring in surgery for adolescent idiopathic scoliosis (AIS) varied on a case-by-case basis, with SSEP monitoring alone being used in 10% of cases, the wake-up test in 1.1%, and no IONM in 0.6%.…”

Intraoperative Neurophysiologic Monitoring Using Evoked Potentials

“…2,3,7,[12][13][14][15] With compression or vascular compromise there tends to be involvement in multiple areas of the cord resulting in changes in the SSEPs that correspond to the damage. 2,3,7,[12][13][14][15] With compression or vascular compromise there tends to be involvement in multiple areas of the cord resulting in changes in the SSEPs that correspond to the damage.…”