Intraoperative monopolar mapping during 5-ALA–guided resections of glioblastomas adjacent to motor eloquent areas: evaluation of resection rates and neurological outcome
Philippe Schucht, Kathleen Seidel, Jürgen Beck, Michael Murek, Astrid Jilch, Roland Wiest, Christian Fung, Andreas Raabe
A growing body of evidence indicates that surgery prolongs survival in glioblastoma patients if an extensive part of the contrast-enhancing tumor is resected, 21, 34, 49 although all therapies for glioblastoma are essentially palliative for most patients. 51 The greatest survival benefit is observed in patients with complete resection of enhancing tumor (CRET). 41 However, removal of the final 1%-2% of the contrast-enhancing tumor carries not only the greatest impact from an oncological point
... view 20, 42, 44, 45 but also the greatest risk for neurological impairment, especially in glioblastomas adjacent to motor eloquent areas. Several newly developed technical procedures, such as the use of 5-aminolevulinic acid (5-ALA) 41 and intraoperative MRI, 39 have been proven to increase the rate of CRET, leading resections deeper into the white matter, which in turn endangers neurological function. Balancing the oncological benefit of more extensive resections and the prerequisite of sparing neurological functionality (maximum safe resection) is particularly challenging in patients with glioblastoma close to the corticospinal tract (CST). Electrical stimulation is a validated intraoperative technique for identifying motor eloquent areas. 1,3,29 Inter-Object. Resection of glioblastoma adjacent to motor cortex or subcortical motor pathways carries a high risk of both incomplete resection and postoperative motor deficits. Although the strategy of maximum safe resection is widely accepted, the rates of complete resection of enhancing tumor (CRET) and the exact causes for motor deficits (mechanical vs vascular) are not always known. The authors report the results of their concept of combining monopolar mapping and 5-aminolevulinic acid (5-ALA)-guided surgery in patients with glioblastoma adjacent to eloquent tissue. Methods. The authors prospectively studied 72 consecutive patients who underwent 5-ALA-guided surgery for a glioblastoma adjacent to the corticospinal tract (CST; < 10 mm) with continuous dynamic monopolar motor mapping (short-train interstimulus interval 4.0 msec, pulse duration 500 msec) coupled to an acoustic motor evoked potential (MEP) alarm. The extent of resection was determined based on early (< 48 hours) postoperative MRI findings. Motor function was assessed 1 day after surgery, at discharge, and at 3 months. Results. Five patients were excluded because of nonadherence to protocol; thus, 67 patients were evaluated. The lowest motor threshold reached during individual surgery was as follows (motor threshold, number of patients): > 20 mA, n = 8; 11-20 mA, n = 13; 6-10 mA, n = 10; 4-5 mA, n = 13; and 1-3 mA, n = 23. Motor deterioration at postsurgical Day 1 and at discharge occurred in 30% (n = 20) and 10% (n = 7) of patients, respectively. At 3 months, 3 patients (4%) had a persisting postoperative motor deficit, 2 caused by vascular injury and 1 by mechanical injury. The rates of intra-and postoperative seizures were 1% and 0%, respectively. Complete resection of enhancing tumor was achieved in 73% of patients (49/67) despite proximity to the CST. Conclusions. A rather high rate of CRET can be achieved in glioblastomas in motor eloquent areas via a combination of 5-ALA for tumor identification and intraoperative mapping for distinguishing between presumed and actual motor eloquent tissues. Continuous dynamic mapping was found to be a very ergonomic technique that localizes the motor tissue early and reliably. Key WorDS • corticospinal tract • glioblastoma • tumor surgery • intraoperative neuromonitoring • motor evoked potential • subcortical mapping Abbreviations used in this paper: CRET = complete resection of enhancing tumor; CST = corticospinal tract; CUSA = Cavitron Ultrasonic Surgical Aspirator; DCS = direct cortical stimulation; EEG = electroencephalography; GTR = gross-total resection; KPS = Karnofsky Performance Scale; MEP = motor evoked potential; MRC = Medical Research Council; MT = motor threshold; SSEP = somatosensory evoked potential; STR = subtotal resection; TES = transcranial electrical stimulation; TOF = train of five; 5-ALA = 5-aminolevulinic acid.