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01.09.2009 | Clinical Article | Ausgabe 9/2009

Acta Neurochirurgica 9/2009

Validity of primary motor area localization with fMRI versus electric cortical stimulation: A comparative study

Zeitschrift:
Acta Neurochirurgica > Ausgabe 9/2009
Autoren:
Robert Bartoš, Robert Jech, Josef Vymazal, Pavel Petrovický, Petr Vachata, Aleš Hejčl, Amir Zolal, Martin Sameš
Wichtige Hinweise

Comment

The authors report a series of 18 consecutive patients who underwent surgery for a central tumor. Using a neuronavigation system, they compared the results provided by preoperative motor functional MRI (fMRI) and intraoperative electrical stimulation. They showed that the fMRI sensitivity for localizing the primary motor cortex detected by electrostimulation was 71%.
Although such comparison has been made in many previous studies, the present results provide additional arguments supporting the fact that fMRI is not so reliable. The mechanisms of such low reliability have been well discussed by the authors. Therefore, on the basis of these data, it is important to keep in mind that intraoperative electrical mapping remains the gold standard, and that neurosurgeons have to be cautious when using solely fMRI for brain surgery within eloquent areas, even in motor region—indeed, it has already been demonstrated that the reliability of fMRI was poor for language and cognitive functions. As a consequence, combination of “classical” intrasurgical electrophysiology with new neuroimaging methods (fMRI and diffusion tensor imaging) is presently still mandatory.
Hugues Duffau,
Montpellier, France

Abstract

Background

Functional magnetic resonance imaging (fMRI) is a widely used method for research and visualization of the brain function. However, its clinical use is still limited. Our objective was to study fMRI reliability in localizing the primary hand motor cortex (M1) under pathological conditions caused by the proximity of a brain tumour. The results were then compared with standard technique of cortical function mapping—electric cortical stimulation (ECS).

Method

We compared M1 areas localized with the fMRI and ECS in 18 patients with brain tumours in fronto-parietal regions. The 1.5 T blood oxygenation-level dependent (BOLD) fMRI was performed preoperatively using a motor task involving rhythmic touching of the thumb consecutively with other fingers on the same hand contralateral to the affected hemisphere. Each individual fMRI result was displayed at the P < 0.05 significance level corrected for family wise error (more conservative approach) or at the P < 0.001 level uncorrected (less conservative approach) and projected on the T1-weighted image used for neuronavigation.

Findings

In 12 patients (66.6%) we found full agreement between the fMRI and ECS. In 3 patients (16.6%) the overlap was only partial, with one ECS testing position on motor response found outside the BOLD signal cluster. In another 3 cases (16.6%) there was a discrepancy between the two methods. The fMRI sensitivity for localizing the ECS reactive M1 cortex was 71%. The fMRI/ECS consistency was within a 5-mm range in 77% of the testing positions used for ECS which complies with the inherent accuracy of the navigation system.

Conclusions

Because the overlap between the two methods never exceeded 10-mm, we found that the fMRI method correctly guided the ECS to the M1 cortex in 83% of patients. Infiltrative growth of the tumour and collateral oedema were the reasons for the BOLD signal suppression in three patients. Our results support using ECS as a more reliable tool for M1 cortical mapping than fMRI.

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