Functional Magnetic Resonance Imaging (fMRI) in Brain Tumour Patients
European Association of NeuroOncology Magazine 2012; 2 (3): 123-128
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Keywords: brain mapping, brain neoplasms, functional, glioma, magnetic resonance imaging, motor cortex
Functional magnetic resonance imaging (fMRI) is increasingly used in the work-up of brain tumour patients preoperatively to assess the relationship between the functionally eloquent cortex and brain pathology. In cases of presumed tumour localisation in or near eloquent brain areas, such as the motor cortex or language areas, fMRI may be advantageous to guide the neurosurgical approach, shorten surgery duration, and obtain prognostic information prior to surgery. For the assessment of the primary motor cortex a good correlation between fMRI and intraoperative electrocortical mapping (ECM) has been reported, with sensitivities and specificities ranging from 88–100 %. For the localisation of language representation areas validation results are controversial with sensitivities from 22–100 % and specificities from 0–100 %, rendering fMRI less suitable as the sole technique for language cortex localisation. For the assessment of hemispheric language lateralisation, however, > 90 % agreement between fMRI and the invasive Wada test has led to fMRI now mostly having replaced the Wada test for this indication. There are several limitations of fMRI including issues that are inherent to the technique such as spatial and geometric uncertainty, tumour effects on the fMRI signal, interand intra-individual variability, lack of discrimination between essential and modulating brain regions, and lack of information on the underlying white matter. Such shortcomings need to explicitly be taken into account in every patient. The careful use of fMRI is justified to aid neurosurgical planning but intraoperative ECM remains the gold standard for localising the eloquent brain cortex.