Correlation between glymphatic dysfunction and cranial defect in severe traumatic brain injury: a retrospective case-control study based on a diffusion tensor image analysis along the perivascular space (DTI-ALPS) investigation

Background: To date, limited research has been conducted on the functionality of the glymphatic system during the recovery phase of severe traumatic brain injury (sTBI). This study aimed to use a diffusion tensor image analysis along the perivascular space (DTI-ALPS) to evaluate glymphatic system function in patients recovering from sTBI who underwent unilateral decompressive craniectomy, and to examine the correlation between the ALPS index and the size of the cranial defect. We hypothesized that assessments would reveal ongoing impairments in glymphatic system function among sTBI patients during the recovery phase. Methods: A total of 23 patients with a history of sTBI who had previously undergone unilateral decompressive craniectomy at Xiangya Hospital of Central South University from January 2020 to December 2020 were enrolled in the study, along with 33 healthy control (HC) subjects. All the subjects underwent magnetic resonance imaging (MRI) with DTI scans, and the ALPS index was subsequently calculated to assess glymphatic system functionality. Additionally, the circumference and sectional area of the cranial defect were measured for each patient. An analysis of variance (ANOVA) was used to compare the ALPS index values between the sTBI patients and HC subjects, while a Pearson correlation analysis was used to examine the correlation between the ALPS index and cranial defect characteristics. Results: The ALPS index values of both the craniectomy side (t=-9.08, P<0.001) and non-craniectomy side (t=-5.06, P<0.001) of the sTBI group were significantly lower than those of the HC group. However, no statistically significant differences were observed between the ALPS index values of the craniectomy and non-craniectomy sides. Additionally, no significant differences were observed in the ALPS index values of both the craniectomy and non-craniectomy sides among the early, intermediate, and late recovery phases. In the sTBI patients, a moderately strong negative correlation was found between the circumference of the cranial defect and the ALPS index of the craniectomy side (r=-0.62, P=0.002), and a moderately negative correlation was found between the sectional area of the cranial defect and the ALPS index of the craniectomy side (r=-0.56, P=0.005). = 0.005). Conclusions: The non-invasive DTI-ALPS technique revealed significantly reduced ALPS index values during the recovery phase of sTBI, indicating persistent impairment in glymphatic system function. A significant negative correlation was found between the ALPS index value of the craniectomy side and the size of the cranial defect. These findings suggest that the ALPS index may serve as a valuable prognostic factor in the recovery phase of sTBI.