Computed tomography-based symmetry in bilateral chronic subdural hematomas: Its prognostic significance

Previous studies have suggested that bilateral chronic subdural hematomas (CSDH) have higher recurrence rates and poorer postoperative prognosis than unilateral CSDH. The present study aimed to investigate the significance of bilateral symmetry in computed tomography (CT) findings in patients with bilateral CSDH to identify patients who are at high risk of poor outcomes. This study included 160 individuals who underwent burr hole surgery for symptomatic bilateral CSDH at two medical centers between January 2019 and December 2023. We collected data on demographics, preoperative blood tests, treatment outcomes, and CT scans. Hematomas were categorized into homogeneous, laminar, separate, and trabecular types according to Nakaguchi's classification. The concordance rate between the CT classifications of bilateral hematomas was significantly higher than would be expected under the assumption that those are independent between right and left. Albumin levels were significantly lower in individuals with bilateral symmetric hematomas than those with asymmetric hematomas. Logistic regression identified hypoalbuminemia as the only independent predictor of bilateral symmetry (odds ratio 3.79, 95 % confidence interval 1.04-18.5, p = 0.04). Although recurrence rates did not significantly differ between symmetric and asymmetric cases, the proportion of patients with modified Rankin Scale 3-6 was significantly higher in those with symmetric hematomas than in those with asymmetric hematomas (49.2 % vs. 25.0 %, p = 0.008). Additionally, preoperative albumin levels were significantly lower in patients with poor outcomes (mRS 3-6) than in those with favorable outcomes (mRS 0-2) (4.1 [IQR 3.8-4.4] vs. 3.7 [3.3-4.0], p < 0.0001). Multivariate analysis revealed that hypoalbuminemia was an independent risk factor for poor outcomes (odds ratio 7.14, 95 % CI 3.17-17.5, p < 0.0001). Bilateral symmetric CSDH may indicate more severe systemic dysfunction and worse treatment outcome. The association between specific CT patterns, hypoalbuminemia, and adverse outcomes helps in identifying patients who are at high risk and may benefit from tailored management strategies.