Elsevier

World Neurosurgery

Volume 95, November 2016, Pages 108-116
World Neurosurgery

Literature Review
Neuromonitoring for Intramedullary Spinal Cord Tumor Surgery

https://doi.org/10.1016/j.wneu.2016.07.066Get rights and content

Background

Intramedullary spinal cord tumors (IMSCT) account for about 2%–4% of tumors of the central nervous system. Surgical resection continues to be the most effective treatment modality for most intramedullary tumors, with gross total resection leading to preserved neurologic function and improved survival. However, surgical treatment is often difficult and carries significant risk of postoperative neurologic complications. Intraoperative neuromonitoring has been shown to be of clinical importance in the surgical resection of IMSCT. The main monitoring modalities include somatosensory evoked potentials, transcranial motor evoked potentials via limb muscles or spinal epidural space (D-waves), and dorsal column mapping. These monitoring modalities have been shown to inform surgeons intraoperatively and in many cases, have led to alterations in operative decision.

Methods

We reviewed the literature on the usefulness of intraoperative neuromonitoring for intramedullary spinal tumor resection and its role in predicting postoperative neurologic deficits. A MEDLINE search was performed (2000–2015) and 13 studies were reviewed. Detailed information and data from the selected articles were assessed and compiled. Data were extracted showing the role of monitoring in outcomes of surgery.

Conclusions

By using intraoperative somatosensory evoked potentials, transcranial motor evoked potentials, D-waves, and dorsal column mapping, spinal injury could be prevented in most cases, thereby improving postoperative neurologic functioning and outcome in patients undergoing surgery for IMSCT.

Introduction

Intramedullary spinal cord tumors (IMSCT) account for about 2%–4% of tumors of the central nervous system and about 15% of adult intradural tumors.1, 2, 3, 4, 5 The most common IMSCT include ependymomas and astrocytomas. Unlike most brain tumors, these tumors are often benign and have an insidious onset, with presenting symptoms including paresthesia, weakness, spasticity, gait instability, and bowel/bladder dysfunction. Surgical resection continues to be the most effective treatment modality for most intramedullary tumors, with gross total resection leading to preserved neurologic function and improved survival.2, 6, 7 However, surgical treatment is often difficult and carries significant risk of postoperative neurologic complications. Studies have reported deterioration in neurologic function in patients postoperatively,4, 8, 9 with rates of dorsal column dysfunction as high as 43.6%–55.1%.4, 10, 11 These deficits severely affect the postoperative functionality of patients because they are often left with significant morbidity, worse than their preoperative disease burden.12, 13, 14 Part of the surgical difficulty stems from the inability to identify the appropriate resection plane to delineate the extent of resection. Also, the presence of tumor can distort the normal anatomic architecture of the spinal cord, making it difficult to ascertain the physiologic midline for a myelotomy. As a result of these surgical challenges, intraoperative neuromonitoring (IONM) has gained favorable grounds in facilitating maximal tumor resection and minimizing neurologic morbidity.15, 16, 17, 18

IONM has been shown to be of clinical importance in the surgical resection of intramedullary spinal cord tumors.17, 19, 20, 21, 22, 23, 24 The main monitoring modalities include somatosensory evoked potentials (SSEPs), transcranial motor evoked potentials (TcMEPs) via limb muscles or spinal epidural space (D-waves), and dorsal column mapping (DCM). SSEPs provide information about the functionality of sensory pathways. Despite earlier studies showing reduction of quadriplegia from 3.7% to 0%25 and from 6.8% to 0.7%26 using intraoperative SSEP monitoring, postoperative deficits were being reported regardless of the unchanged intraoperative SSEP.27, 28, 29, 30 As a result, TcMEP has been used as a direct method of monitoring motor pathways during surgery for intramedullary spinal tumor and other spinal diseases.31, 32, 33 Consequently, the combined use of SSEP and motor evoked potential (MEP) provides increased accuracy in detecting injury to sensory and motor pathways that can be affected differently depending on the location and morphology of the tumor.34, 35 DCM using microstimulation and SSEP recording is another modality being used to determine anatomic landmarks such as the dorsal median sulcus to guide midline myelotomy. These monitoring modalities have been shown to inform surgeons intraoperatively and in many cases have led to alterations in operative decision. Herein, we reviewed the literature on the usefulness of IONM for intramedullary spinal tumor resection and its role in predicting postoperative neurologic deficits.

Section snippets

Methods

The MEDLINE database was queried using the following search items: “intramedullary tumor”, “spine”, “spinal tumor”, “monitoring”, “neuromonitoring”, “somatosensory evoked potential”, “motor evoked potential”, and “dorsal column mapping”. Only articles in English published between 2000 and 2015 were considered. Publications excluded from our search were non-English articles, abstract-only publications, or articles not available via our electronic database queries. Individual case reports were

Results

After an extensive search for available articles, 13 studies were selected for inclusion in this review. Table 1 shows a summary of the relevant clinical studies and the intraoperative monitoring modalities and postoperative changes in neurologic status. One of the articles (study 1) was a historical control study in which patients who underwent surgery for intramedullary spinal tumor with intraoperative monitoring were matched and compared with previously operated patients without monitoring.

Discussion

Surgical resection for intramedullary spinal tumors remains a challenging operative dilemma and the extent of resection is often sacrificed for impending neurologic damage. Studies have reported transient and permanent neurologic impairment after resection of these tumors.6, 30 With the steady increase in microsurgical techniques, diagnostic imaging, and intraoperative monitoring modalities, there has been a decline in postoperative neurologic morbidities in patients undergoing surgery for

Conclusions

IONM using modalities including DCM, SSEP, muscle TcMEP, and D-waves (or a combination thereof) provides surgeons with anatomic landmarks for midline myelotomy, indications of the resection plane, and guidance to the extent of maximum tumor resection with minimal neurologic morbidity. Studies continue to show favorable postoperative outcomes when these monitoring modalities are used in combination. However, combining modalities leads to variability in false-positive and false-negative results

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    Conflict of interest statement: The authors declare that the article content was composed in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.

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