Somatotopic organization of corticospinal/corticobulbar motor tracts in controls and patients with tumours: A combined fMRI-DTI study.

Objectives: To investigate the relative somatotopic organization of the motor corticospinal/corticobulbar foot, hand, lip and tongue fascicles by combining fMRI with DTI and to examine the influence of subjacent intrinsic tumours on these fascicles.

Methods: The study was approved by the local ethics committee. Seven male and three female volunteers (median age: 35 years) and one female and eight male patients with brain tumours (median age: 37 years) were scanned on a 1.5-T MRI scanner. fMRI data, analysed using SPM5, identified the motor task-driven fMRI grey matter activations of the hand, foot, lips and tongue as seed regions for probabilistic tractography. The relationship between the components of the CST was assessed and the distances between them were measured. A statistical comparison was performed comparing these distances in the group of healthy hemispheres with those of the group of non-affected hemispheres and healthy hemispheres.

Results: Hand fascicles were identified in all subjects (38/38, 100%), followed by foot (32/38, 84%), lip (31/38, 81%) and tongue fascicles (28/38, 74%). At superior levels, the hand fascicles were anterolateral to the foot fascicles in 77-93% of healthy hemispheres (HH), in 50-71% of non-affected patients' hemispheres (pH) and in 67-89% of affected PH. At inferior levels, the hand fascicles were either anteromedial in 46-45% of HH or anterior in 75% of non-affected PH and in 67-83% of affected PH. Tongue and lip fascicles overlapped in 25-45% of HH, in 10-20% of non-affected PH and in 15-25% of affected PH. No significant difference was found between the group of affected hemispheres and that of healthy and non-affected hemispheres.

Conclusion: The somatotopy of the hand fascicles in relation to the foot fascicles was anterolateral in patients and volunteers at superior levels but anteromedial in volunteers and mostly anterior in patients at inferior levels. The lip and tongue fascicles generally overlapped. Intracranial tumours displaced the motor fascicles without affecting their relative somatotopy.