External validation and modification of the Oslo grading system for prediction of postoperative recurrence of chronic subdural hematoma

Recently, Oslo grading system (OGS) for prediction of recurrence in chronic subdural hematoma (cSDH) was introduced. The aim of the study was to validate and if applicable to modify the grading system. Data of all patients admitted to the Goethe University Hospital between 2016 and 2018 with chronic subdural hematoma were prospectively entered into a database. Dataset of patients with uni- (n = 272) and bilateral cSDH (n = 177) were used for the validation of OGS via logistic regression analysis. Additional predictors were identified and integrated to build a modified OGS (mOGS). Internal validation of the modified OGS was performed using same dataset of patients. The OGS showed a significant good predictive value with correlating increase of recurrence rate depending on the level of score in unilateral cSDH (p = 0.002). Regarding bilateral cSDH, there was no significant predictive value found (p = 0.921). By performing uni- and multivariate analysis, additional predictors for recurrence in uni- and bilateral cSDH were identified and integrated into the score system. Accordingly, the mOGS for unilateral cSDH inherited 4 components: previous OGS with 3 components (OR1.6) and seizure (OR2.5) (0 point, 0% recurrence rate; 1–2 points, 17.4%; 3–4 points, 30.6%; ≥ 5 points, 80%). Regarding bilateral cSDH, the mOGS consisted of 4 components as well: hypodense/gradation subtypes (OR3.3), postoperative unilateral volume > 80 mL (OR7.4), postoperative unilateral air trapping > 80 mL (OR15.3), and seizure (OR5.5) (0 point, 3.6% recurrence rate; 1 point, 30.6%; 2 points, 53.5%; 3 points, 58.3%; ≥ 4 points, 100%). Furthermore, the mOGS was internally verified showing high significant predictive power for recurrent hematoma in uni- (p = 0.004) and bilateral cSDH (p < 0.001). External validation of OGS showed accurate risk stratification of recurrence in unilateral cSDH; however, the validation failed for bilateral cSDH. Thus, mOGS was developed to strengthen its clinical utility and applicability.