The value of intraoperative neurophysiological monitoring for microsurgical removal of conus medullaris lipomas: a 12-year retrospective cohort study.

Olaf Suess,Stefanie Hammersen,Sven Mularski,Marcus A Czabanka,Mario Cabraja,Theodoros Kombos

doi:10.1186/s13037-014-0035-4

Abstract

BackgroundLipomas in the lower spinal canal can lead to progressive neurological deficits, so they may have to be surgically removed. Intraoperative neurophysiological monitoring serves to minimize the morbidity of the surgical procedure. However, so far there are no evidence-based recommendations which type of monitoring procedure or combination of procedures to choose.MethodsThe aim of this study was to evaluate the feasibility and value of various intraoperative monitoring techniques: motor and sensory evoked potentials (MEP, SEP), free-running and triggered electromyography (EMG). Thirty cases of spinal lipomas of the Conus medullaris (dorsal Type A: 20.0%; caudal Type B: 33.3%; transitional Type C: 46.7%) were retrospectively evaluated over a 12-year period.ResultsThe patients were mostly pediatric and suffered from persistent pain (73.3%), pareses (56.7%), sensory deficits (43.4%), and/or urogenital dysfunctions (60.0%). SEPs were successfully evoked in 66.7% of cases, MEPs in 86.7% of cases, and EMGs in 100%. MEP alterations correlated with direct mechanical maneuvers in the operating site. SEP changes correlated mostly with physiological events, such as rinsing/cooling of the operating site. Spike-, burst- or tonic train-activity was found in the free-running EMG that occurred only with certain manipulation patterns. Irreversible MEP changes and signal loss in the triggered EMG correlated with post-operative deficits.ConclusionsThe results of this study showed, that intraoperative monitoring could be considered a helpful tool during lipoma tumor surgery near the Conus medullaris. Most reliable results were obtained from transcranial MEPs, free-running EMGs, and triggered EMGs. That’s why the authors favor a routine set-up consisting of at least these three techniques, as this enables mapping at the beginning of the operation, continuous functional testing during surgery, and prognosis of the post-operative symptomology.

Highlights

Lipomas in the lower spinal canal can lead to progressive neurological deficits, so they may have to be surgically removed
Lipomas of the Conus medullaris are the most common form. They occur with an incidence of 1 in 4000 births in Western countries, and they have a 2:3 male:female ratio [1,5]. They are categorized into three subgroups, depending upon where they adhere to the Conus: a) dorsal, b) caudal, and c) transitional (Figure 2) [1,2,4,5]
Patients Patients were included in the analysis who had to undergo a neurosurgical operation for a lipoma in the area of the Conus medullaris under intraoperative Motor evoked potentials (MEPs)/Somatosensory evoked potentials (SEPs)/EMG monitoring

Summary

Introduction

Lipomas in the lower spinal canal can lead to progressive neurological deficits, so they may have to be surgically removed. Spinal lipomas are benign tumors of the spinal canal. They consist of up to 90% fat cells but can contain fibrous, muscular, neural, and other embryogenic tissue. Lipomas of the Conus medullaris are the most common form They occur with an incidence of 1 in 4000 births in Western countries, and they have a 2:3 male:female ratio [1,5]. They are categorized into three subgroups, depending upon where they adhere to the Conus: a) dorsal, b) caudal, and c) transitional (Figure 2) [1,2,4,5].

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