gms | German Medical Science

Objective: Diffusion tensor imaging fiber tracking (DTI FT) is becoming increasingly important for detecting functionally relevant subcortical pathways during surgical planning for the resection of motor-eloquent brain tumors. The present study investigates whether the distance between the tumor and the corticospinal tract (CST) is related to motor function deficits and could therefore be used to assess the postoperative risk of paresis.

Method: Overall, 56 high-grade glioma (HGG) patients, 20 low-grade glioma (LGG) patients, and 21 patients suffering from intracranial metastases (M) were included (median age: 56.6 years, 43 female and 54 male patients). All patients underwent preoperative motor mapping by navigated transcranial magnetic stimulation (nTMS), and all stimulation spots that elicited a motor evoked potential (=motor-positive spots) were exported for subsequent DTI FT using a standardized fractional anisotropy threshold (FAT) tracking protocol. The motor-positive spots were defined as regions of interest (ROIs), and distances between the tracked CST and the lesion were measured. The distances were then compared to the patients’ respective motor status.

Results: The patients with preoperative paresis showed lower distances to the CST in general. However, only the comparison for metastases patients was statistically significant (4.5 ± 9.2 vs. 14.7 ± 9.8 cm, p=0.01). When analyzing minimum (MIN) and maximum (MAX) distances for surgery-related paresis, HGG patients without paresis showed higher distances to the CST when compared to their counterparts with transient or permanent motor deficits (MIN / MAX: no deficit: 0.0 / 38.3 cm; transient deficit: 5.5 / 22.7 cm; permanent deficit: 0.0 / 11.4 cm). A similar trend was revealed for M patients (MIN / MAX: no deficit: 0.0 / 29.2 cm; transient deficit: 0.0 / 0.0 cm; permanent deficit: none) and LGG patients (MIN / MAX: no deficit: 0.0 / 21.8 cm; transient deficit: none; permanent deficit: 0.0 / 1.3 cm) although these patient groups were smaller.

Conclusions: Patients without deficits showed higher distances when compared to their counterparts with deficits in general. Yet, statistically significant differences could only be observed for metastases patients preoperatively, thus showing that our imaging approach matched with clinical status. Hence, no cutoff value for the minimal distance between the tumor and the CST that would allow for prediction of motor deficits with a positive predictive value of 100% was revealed.