LAUSR

We thank Dr. DavideNasi for his review of our article, BSpinal intradural extramedullary tumors: the value of intraoperative neurophysiologic monitoring on surgical outcome^ [1]. Utilization of new technologies in the surgical field often enhances surgical capabilities and improves outcome, but in other cases proves to be unnecessary. Intraoperative monitoring (IOM) in spine surgery was proven to prevent neurological injuries in deformity and intramedullary spinal cord tumor surgery, yet the technology is widely used for other spinal operations as well, increasing surgical costs and possibly monitoring induced morbidity. Our study compared historical control surgeries for intradural extramedullary tumors (IDEM) that were operated with no monitoring with a series of cases operated with IOM. The acute neurological deterioration was statistically similar in both groups. Being benign tumors, the primary goal of surgery is to maximize resection and to decompress the spinal cord and nerves with minimal iatrogenic neurological damage. According to that philosophy, a tumor compressing the cord should be resected to achieve sufficient decompression even if the IOM deteriorates. Dr. Nasi raised very interesting points; the first being the utilization of D-waves for IDEM tumor resection. Unlike muscle-MEP recording which predicts any postoperative motor deficit, D-wave recording is used to determine which deficits will remain long term. D-waves are shown to be effective for intramedullary spinal cord tumors since a large percentage of these patients suffer from expected and accepted short-term impairment, and aggressive resection improves the oncological and functional prognosis. The D-wave technique identifies impending long-term deficits, with the objective of preventing them while maximizing aggressive resection. Since IDEM tumors are benign, and sub-total resection is acceptable to prevent significant shortor long-term neurological deficit, we do not see the added value of D-waves to muscle-MEP. Dr. Nasi mentioned the short follow-up period in our study as a major limitation. Indeed, a longer follow-up time would allow better understanding of the clinical course; however, being a referral center, our institution often lacks the comprehensive conditions allowing for long-term assessment. As stated above, short-term neurological deficits should be minimized following IDEM resection; hence, we feel that immediate neurological status is of importance. The third point in the response letter quotes a paper by Westwick et al. [2] reviewing spinal meningioma literature. The authors identified 16 surgical series, of which only 4 used IOM. The average rate of neurological deterioration was 6%, ranging 0–21%. Dr. Nasi states: BIn our opinion, this data represents a sufficient motivation for the use of IOM in IDEM.^ Obviously, if IOM is proven to prevent neurological deficits, the motivation for its use is clear. The question we discussed in our paper is whether IOM has a positive and statistically significant impact on motor outcome, and based upon our findings, the answer is still unclear. The fourth point raised by Dr. Nasi is modifying of surgical strategy to mitigate neurological deficits. In all cases of an IOM alarm during surgery, blood pressure was elevated and steroids were administered. Our surgical approach includes sufficient bone resection to refrain from cord retraction, so * Ran Harel [email protected]