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3.5/6SH: Multicenter Real-World Derivation and External Validation of a CT-Based Formula for Chronic Subdural
Tao Liu1,2, Biao Zhao3, Yang Liu4
1Department of Neurosurgery, Xuanwu Hospital, Capital Medical University, Beijing, China.
Insights
A new 3.5/6SH formula accurately estimates chronic subdural hematoma (cSDH) volume at the bedside, outperforming the traditional 1/2ABC method. This simplified approach offers reliable assessment for clinical practice and research.
Area of Science:
- Neurosurgery
- Radiology
- Medical Imaging Analysis
Background:
- Accurate hematoma volume estimation in chronic subdural hematoma (cSDH) is critical for clinical decision-making.
- The conventional 1/2ABC formula may lack accuracy for cSDH due to its irregular morphology.
- A need exists for a rapid, reliable, and practical bedside method for cSDH volume assessment.
Purpose of the Study:
- To compare the accuracy and reliability of seven simplified computed tomography (CT)-based formulas for cSDH volume estimation against a 3D Slicer reference standard.
- To evaluate a newly proposed 3.5/6SH formula in both derivation and independent validation cohorts.
- To assess the efficiency and reproducibility of the 3.5/6SH formula for bedside application.
Main Methods:
- A post-hoc analysis of a multicenter, real-world study involving 129 patients in the derivation cohort and 60 in the validation cohort.
- Comparison of seven simplified CT-based formulas, including the 3.5/6SH and 1/2ABC formulas, with 3D Slicer volumetric measurements.
- Evaluation using estimation error, percentage deviation, intraclass correlation coefficients (ICCs), and Bland-Altman (BA) analysis for accuracy, agreement, and efficiency.
Main Results:
- The 3.5/6SH formula demonstrated the lowest median volume deviation (-0.82 mL) and percentage deviation (-1.00%) with the highest ICC (0.973) in the derivation cohort.
- The 3.5/6SH formula showed clinically acceptable limits of agreement (max absolute percentage deviation 29.33%) and maintained high accuracy (ICC=0.979) in the validation cohort.
- The 3.5/6SH formula exhibited excellent inter- and intrarater reproducibility (ICCs > 0.994) and a calculation time of 77.95 seconds, significantly faster than 3D Slicer.
Conclusions:
- The 3.5/6SH formula provides a highly accurate and reliable method for bedside cSDH volume estimation, surpassing the traditional 1/2ABC formula.
- This simplified formula facilitates consistent volume assessment in multicenter research and clinical practice.
- The 3.5/6SH formula is particularly valuable for sensitive monitoring of hematoma changes in resource-limited settings.
Abstract:
Accurate hematoma volume estimation in chronic subdural hematoma (cSDH) is crucial for clinical decision-making. The commonly used 1/2ABC formula, originally developed for small, regular hematomas, may be inaccurate for cSDH due to its irregular morphology. A rapid, reliable, and practical method for bedside assessment is needed. This post hoc analysis of a multicenter, real-world study compared seven simplified computed tomography-based formulas with volumetric measurements obtained using three-dimensional (3D) Slicer in a derivation cohort of 129 patients with cSDH. We further evaluated the newly proposed 3.5/6SH formula in an independent validation cohort of 60 additional patients. Accuracy, agreement, and efficiency were evaluated using estimation error, percentage deviation, intraclass correlation coefficients (ICCs), and Bland-Altman (BA) analysis. In the derivation cohort, the 3.5/6SH formula yielded the lowest median volume deviation (-0.82 mL, interquartile range [IQR] 13.12 mL), the smallest percentage deviation (-1.00%, IQR 17.08%), and the highest ICC (0.973), indicating high accuracy and close agreement with the 3D Slicer reference standard. In contrast, the widely used 1/2ABC formula exhibited a larger negative percentage deviation (-4.64%) and a lower ICC (0.910). BA analysis further confirmed that 3.5/6SH had the narrowest limits of agreement and a clinically acceptable maximum absolute percentage deviation (29.33%), whereas the maximum deviation for 1/2ABC (65.04%) exceeded the clinical acceptability threshold (33%). In an independent validation cohort of 60 patients, 3.5/6SH maintained a small bias (median deviation -1.29 mL; percentage deviation -1.27%) and excellent agreement with 3D Slicer (ICC = 0.979). Inter- and intrarater ICCs for 3.5/6SH measurements in the validation cohort were 0.994 and 0.998, respectively, supporting excellent reproducibility. The average calculation time was 77.95 sec for 3.5/6SH-longer than for 1/2ABC (35.95 sec), but substantially shorter than for 3D Slicer (19.04 min). The 3.5/6SH formula showed high accuracy and agreement with 3D Slicer across all metrics and offers a reliable, simplified method for bedside cSDH volume estimation that may facilitate more consistent volume assessment in multicenter research and clinical practice, particularly for more sensitive monitoring of hematoma changes in resource-limited environments.
