The effect of tumour type and distance on activation in the motor cortex

Abstract

Functional MRI has been widely used to identify the eloquent cortex in neurosurgical/radiosurgical planning and treatment of CNS neoplasms and malformations. In this study we examined the effect of CNS tumours on the blood oxygenation level-dependent (BOLD) activation maps in the primary and supplementary motor cortex. A total of 33 tumour patients and five healthy right-handed adults were enrolled in the study. Patients were divided into four groups based on tumour type and distance from primary motor cortex: (1) intra-axial, near, (2) extra-axial, near, (3) intra-axial, far and (4) extra-axial, far. The intra-axial groups consisted of patients with astrocytomas, glioblastomas and metastatic tumours of mixed histology; all the extra-axial tumours were meningiomas. The motor task was a bilateral, self-paced, finger-tapping paradigm. Anatomical and functional data were acquired with a 1.5 T GE Echospeed scanner. Maps of the motor areas were derived from the BOLD images, using SPM99 software. For each subject we first determined the activation volume in the primary motor area and the supplementary motor area (SMA) and then calculated the percentage difference between the hemispheres. Two factors influenced the activation volumes: tumour type (P<0.04) and distance from the eloquent cortex (P<0.06). Patients in group 1 (intra-axial, near) had the smallest activation area in the primary motor cortex, the greatest percentage difference in the activation volume between the hemispheres, and the largest activation volume in the SMA. Patients in group 4 (extra-axial, far) had the largest activation volume in the primary motor cortex, the least percentage difference in volume between the hemispheres, and the smallest activation volume in the SMA. There was no significant change in the volume of the SMA in any group, compared with controls, suggesting that, although there is a gradual decrease in SMA volume with distance from the primary motor area, the effect on motor reorganisation is minimal. All the tumour patients showed a net loss in total activation volumes (both hemispheres plus SMA) compared with controls. The effect of the tumours on interhemispheric volume differences was: group 1>group 3>group 2>group 4. Within the intra-axial tumours, there was no significant effect of tumour type on the results. We conclude that BOLD-imaged activation volume is affected at least by the interplay of two factors: tumour type and distance from the motor cortex. Further, all tumours may be expected to cause some loss of activation volumes in motor areas. We suggest that, with proper precautions and planning, BOLD functional magnetic resonance imaging (fMRI) maps can be useful in minimising damage to the functional areas.

The Blood Oxygen Level–Dependent Functional MR Imaging Signal Can Be Used to Identify Brain Tumors and Distinguish Them from Normal Tissue

“…These authors suggested that the effect on the signal intensity is due to a "stealing" of blood from the active region. These results are similar to those in previous studies from our laboratory 7 showing a significant effect of malignant tumors on the activation volume in the ipsilateral motor cortex during bilateral finger tapping; the effect also decreased with distance from the tumor.…”

“…5,6 The technique uses a gradient-echo imaging sequence with parameters sensitive to the oxygenation level in blood-that is, it reflects changes in the concentrations of oxy-and deoxyhemoglobin. We, 7 and others, 8,9 have used BOLD fMRI to map motor and other areas to spare eloquent cortex during surgery.…”

Brain Tumors: The Influence of Tumor Type and Routine MR Imaging Characteristics at BOLD Functional MR Imaging in the Primary Motor Gyrus

“…Our findings seem to concur with the hypothesis that abnormal tumor neovasculature, a pathologic hallmark of GBMs, contributes to neurovascular uncoupling, which might lead to a decrease in BOLD functional MR imaging activation at the ipsilateral hemisphere (14,18,19,27). Yet, we draw attention to the fact that the significant interhemispheric difference in BOLD functional MR imaging activation observed in GBMs, but not within metastases and meningiomas, does not prove per se that there is a difference in this respect between the three tumor types.…”

“…Previous smaller-scale studies have suggested that functional MR imaging activation volumes are truncated in the presence of tumors, particularly high-grade gliomas (15,16), thus making functional MR imaging potentially less reliable in peritumoral regions. It has been suggested that in addition to the histopathologic properties, other tumor properties (edema, volume, and location) and factors (prior brain surgery, age, motor deficits, and magnetic field strength) may influence BOLD functional MR imaging activation (17)(18)(19).…”

“…Finally, the other MR imaging features examined, volume of enhancement and tumor location, did not seem to play a role. The explanation may be that BOLD response is inherently a vascular phenomenon, which is marginally affected by tumor size (18,27). However, this should be interpreted with caution, as the exact determination of tumor volumes at routine MR imaging is difficult in gliomas, in which borders are often ill defined (30).…”