To the best of our knowledge, this is the first study to investigate the association between BUN concentration and the recurrence of CSDH after evacuation. Our results indicated that high postoperative BUN concentration was related to the prevalence of CSDH recurrence within 3 months after operation. Therefore, our findings revealed the postoperative BUN concentration could be an available risk factor for CSDH recurrence.
BUN is a waste product of protein catabolism which has been found to be linked with poor outcome and mortality in acute or chronic heart failure. In addition, a study of 3355 AIS patients by You et al observed that higher BUN had a 3.75-fold higher risk of in-hospital mortality. In reviewing the literature, little data was found on the relationship between BUN and recurrence of CSDH. In this study, we observed that cases with a higher BUN exhibited a trend toward a higher recurrence rate of CSDH. Furthermore, elevated BUN was significantly in accord with an enhancive risk of CSDH recurrence and cases with highest BUN (> 6.4 mmol/L) seemed to have a 3.124-fold increase in danger of CSDH recurrence exactly after adjusting for the potential confounders.
The precise mechanisms underlying the association between elevated BUN and CSDH recurrence remained unclear. A potential explanation for this might be that a systemic increase in serum BUN induces intracranial multiple responses, which in turn can produce hematoma expansion and bring out CSDH recurrence. Some studies have revealed that the predictive value of BUN may be induced by its connection with other variables, such as protein intake, protein catabolism, nitrogen production and neurohormonal activation[12, 13]. On the other hand, CSDH was recently suggested to be formatted through complex processes including angiogenesis, fibrinolysis and inflammation, and the recurrence of CSDH follows the same process as formation. Strong evidence has been provided that vascular endothelial growth factor (VEGF) was related to the generation and steady increase of CSDH fluid volume[15–17] as well as the risk of CSDH recurrence. Interestingly, Lin et al observed VEGF expression was positively correlated with BUN. These discoveries might explain the relatively good correlation between elevated BUN and CSDH recurrence.
Compared with CSDH cases without recurrence, our result also showed that CSDH cases with recurrence had significantly high age, which is consistent with the reports of previous studies[7, 20]. However, we found that the older cases were associated with higher BUN and the difference of patient age was not statistically significant after multivariate logistic regression analysis (supplementary table 1). It is indicated that age affects the recurrence of CSDH through the change of BUN.
In addition, reduced fibrinogen was found to be associated with the CSDH recurrence rate (OR = 0.755, 95%CI = 0.575–0.993, P = 0.044) (supplemental table 1). In fact, fibrinogen has been proven to be a potentially available risk factor for postoperative intracranial bleeding[21, 22]. Elevating serum fibrinogen was considered as a valid therapy for intracranial hemorrhage. Moreover, high levels of fibrinogen degradation products (FDPs) have been examined in CSDH fluid[24, 25] and fresh red cells were clearly identified within CSDH fluid, suggesting that bleeding is an essential part of CSDH formation. On the other hand, this study did not reveal significant difference between postoperative atorvastatin use and CSDH recurrence, which is contrary to existing studies[26, 27]. The relationship between atorvastatin administration and CSDH recurrence is still puzzling.
There were also some limitations recognized in the present study. Firstly, this study is a retrospective study and the selection bias is inevitable. Secondly, this is only a single-center clinical finding, which may impact the generalization of the results, thus a further prospective research with planty of patients might be required. Finally, considering that the role BUN played in the CSDH recurrence is still confusing, more studies need to be persued to further and better delineate CSDH formation in the future.