Detection of tumour invasion into the pyramidal tract in glioma patients with sensorimotor deficits by correlation of (18)F-fluoroethyl-L: -tyrosine PET and magnetic resonance diffusion tensor imaging.

PURPOSE

Standard magnetic resonance imaging (MRI) does not depict the true extent of tumour cell invasion in gliomas. We investigated the feasibility of advanced imaging methods, i.e. diffusion tensor imaging (DTI), fibre tracking and O-(2-[(18)F]-fluoroethyl)-L: -tyrosine ((18)F-FET) PET, for the detection of tumour invasion into white matter structures not visible in routine MRI.

METHODS

DTI and fibre tracking was performed on ten patients with gliomas, WHO grades II-IV. Five patients experienced preoperative sensorimotor deficits. The ratio of fractional anisotropy (FA) between the ipsilateral and contralateral pyramidal tract was calculated. Twenty-one stereotactic biopsies from five patients were histopathologically evaluated for the absolute numbers and percentages of tumour cells. (18)F-FET PET scans were performed and the bilateral ratio [ipsilateral-to-contralateral ratio (ICR)] of (18)F-FET-uptake was calculated for both cross-sections of pyramidal tracts and biopsy sites.

RESULTS

The FA ratio within the pyramidal tract was lower in patients with sensorimotor deficits (0.61-1.06) compared with the FA ratio in patients without sensorimotor deficits (0.92-1.06). In patients with preoperative sensorimotor deficits, we found a significantly (p = 0.028) higher ICR of (18)F-FET uptake (1.01-1.59) than in patients without any deficits (0.96-1.08). The ICR of (18)F-FET-uptake showed a strong correlation (r = 0.696, p = 0.001) with the absolute number of tumour cells and a moderate correlation (r = 0.535, p = 0.012) with the percentage of tumour cells.

CONCLUSIONS

Our data show an association between preoperative sensorimotor deficits, increased (18)F-FET uptake and decreased FA ratio in the pyramidal tract. We demonstrated a correlation between tumour invasion and (18)F-FET uptake. These findings may help to distinguish between edema versus tumour-associated neurological deficits and could prevent the destruction of important structures, like the pyramidal tract, during tumour operations by allowing more precise preoperative planning.