Quantification of corticospinal tracts with diffusion tensor imaging in brainstem surgery: Prognostic value in 14 consecutive cases at 3T-MRI

Abstract

quantitative diffusion tensor imaging (DTI) in patients with brainstem cavernoma (BSC) in terms of post-operative outcome. METHODS In this retrospective study of 14 brainstem cavernoma patients we analyzed pre- and postoperative DTI data. White matter tractography (WMT) of corticospinal tracts (CSTs) was performed using the Fiber Assignment by Continuous Tracking (FACT) algorithm and morphologic characteristics of CSTs were compared with clinically assessed motor strength. Fractional anisotropy (FA) and apparent diffusion coefficient (ADC) were measured in ipsi- and contralesional regions of interest (ROIs) at the lesion level, as well as levels caudal and rostral to the lesion. Correlation analysis was performed between lateral index (LI) of ipsi-/contralateral FA and ADC values and patients' motor function. RESULTS Preoperatively, normal morphological features of CSTs corresponded to normal motor function in 4 patients. The other 10 morphologically abnormal pre-operative CSTs didn't show corresponding motor impairment either in pre- or post-operative follow-up period. The sensitivity, specificity, positive predictive and negative predictive values of WMT morphology on pre-operative motor function were 100%, 57.1%, 70% and 100% respectively. The corresponding values on follow-up motor function were 100%, 33.3%, 20% and 100% respectively. The mean FA at lesion level was significantly lower than the corresponding FA at the contralateral hemisphere (P=0.009). In areas caudal to the lesion the same trend yet without statistic significance was observed (P=0.23). There was no significant laterality difference of mean FAs rostral to the level of the lesion. No correlation in LI of FA or ADC in the three anatomic levels with simultaneous and long-term follow up motor function was observed. Restoration of the morphology of the affected CST postoperatively was associated with a trend for decreasing ADC compared to the pre-operative measurements. CONCLUSION Intact CST morphology in DTI predicts a favorable postoperative outcome in patients with BSC. Interrupted CSTs and decreased FA-values correlate well within BSC lesion level, nevertheless morphologic characteristics and diffusion parameter changes cannot predict poor prognosis. Caudal and rostral diffusion parameters can provide more information of the integrity of CSTs compared with morphological study alone.