Diffusion tensor image analysis along the perivascular space may serve as a potential biomarker for differentiating...

Diffusion tensor image analysis along the perivascular space (DTI-ALPS) is a non-invasive technique used to investigate alterations in glymphatic system (GS) function related to glioma. This study aimed to investigate the potential of DTI-ALPS in differentiating tumor recurrence (TR) from pseudoprogression (PsP) in glioma patients and the added value of the ALPS index to diffusion tensor imaging (DTI)-derived metrics.

This retrospective study included 72 patients with histologically proven unihemispheric glioma at initial diagnosis who developed new or persisting enhancing lesions (35 with TR and 37 with PsP) on brain magnetic resonance imaging (MRI) after the completion of chemoradiation following gross total resection (GTR), and 34 matched healthy controls (HCs). Ipsilateral ALPS index, contralateral ALPS index, fractional anisotropy (FA), mean diffusivity (MD), axial diffusivity (AD), and radial diffusivity (RD) were calculated. Group comparisons were made between glioma patients and controls, as well as between TR and PsP. Each DTI metric and ALPS index was assessed via receiver operating characteristic (ROC) analysis in terms of differentiating TR from PsP.

Both the ipsilateral and contralateral ALPS indices in the TR group were significantly decreased compared with those in the HC group (ipsilateral: 1.22±0.16 vs. 1.55±0.17; P<0.001; contralateral: 1.38±0.19 vs. 1.53±0.22; P=0.003). The ipsilateral ALPS index in the PsP group was significantly decreased compared with those in the HC group (1.39±0.19 vs. 1.60±0.23; P=0.001), whereas the contralateral ALPS showed no significant difference between the two groups (1.56±0.23 vs. 1.61±0.23; P=0.378). Both ipsilateral and contralateral ALPS indices were significantly lower in the TR group than in the PsP group (P=0.001; P=0.001). DTI metrics also showed significant differences between the TR group and PsP group (P<0.05). The ipsilateral and contralateral ALPS indices demonstrated good discriminative ability between the TR group and PsP group with area under the curve (AUC) values of 0.734 and 0.706, respectively. Furthermore, combining the ALPS index with DTI metrics improved diagnostic performance. The ipsilateral ALPS index combined with FA achieved the highest AUC of 0.852 compared to that of 0.690-0.767 for a single DTI metric. The contralateral ALPS index combined with RD yielded the highest AUC of 0.819 compared to that of 0.704-0.728 for a single DTI metric.

Both ipsilateral and contralateral ALPS indices have the potential to serve as useful imaging biomarkers and add value to DTI metrics in distinguishing TR from PsP. However, a comprehensive interpretation of alterations in the ALPS index is necessary to understand its complex nature, and further investigations are warranted.