Independent external validation of the foramen magnum meningioma risk score: limited discrimination and overestimation of absolute risk
- 1epartment of Neurological Surgery, School of Medicine and Public Health, University of Wisconsin-Madison, Madison, WI, United States
Abstract
ObjectiveForamen magnum meningiomas (FMMs) cause substantial operative morbidity because of their close relationship to the brainstem, lower cranial nerves, vertebral artery (VA), and upper cervical spinal cord. The Foramen Magnum Meningioma Risk Score (FMMRS) is the only published preoperative, MRI-based model for estimating postoperative complication risk. However, it has not been independently validated, and its calibration is unknown. We performed independent external validation, focusing on absolute risk transportability.MethodsIn this single-center, retrospective study, 40 consecutive adults who underwent microsurgical FMM resection were analyzed. The FMMRS was recalculated de novo from preoperative MRI by a neurosurgeon blinded to outcomes, with independent re-scoring by a second neurosurgeon. The primary outcome was any postoperative complications; a major complication was a prespecified secondary outcome. Discrimination was assessed using the area under the receiver operating characteristic curve (AUC) and calibrated the primary outcome using the calibration slope and intercept, the Brier score, and observed-vs-expected rates across the published risk groups.ResultsComplications occurred in 14/40 patients (35.0%) with major complications in 7/40 (17.5%). Point estimates suggested limited discrimination for both endpoints (AUCs of 0.64 [95% CI 0.46–0.79] and 0.67 [95% CI 0.48–0.84]), with confidence intervals that did not exclude chance. Observed complication rates were lower than predicted in the intermediate- and high-risk groups, indicating an overestimation of absolute risk. The calibration slope was 0.23 (95% CI − 0.04 to 0.57), the intercept −0.90 (95% CI − 1.45 to −0.57), and the Brier score (0.333) exceeded that of the null model (0.228). The largest discrepancy was in the high-risk group, where the expected rate was 96.4% vs. an observed rate of 42.9% (95% CI 21.4–67.4%). In exploratory threshold analysis, FMMRS ≥6 captured all major complications, whereas the published high-risk threshold of ≥8 missed approximately half.ConclusionIn this independent external cohort, the FMMRS retained only limited value as an ordinal stratifier for complication risk and overestimated absolute complication probabilities, particularly for high-risk patients. Its published probabilities should not guide individualized preoperative counseling without recalibration; larger multicenter studies with patient-level data are needed to refine and validate a clinically reliable preoperative prediction model.
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BibTeX
@article{sanlier2026independent,
title = {{Independent external validation of the foramen magnum meningioma risk score: limited discrimination and overestimation of absolute risk}},
author = {Nafiye Sanlier and Umid Sulaimanov and Ufuk Erginoglu and Behman Demir and Ahmed Rasim Bayramoglu and Mariagrazia Nizzola and Abdullah Keles and Mustafa K. Baskaya},
journal = {Frontiers in Neurology},
year = {2026},
month = oct,
doi = {10.3389/fneur.2026.1926742},
url = {https://doi.org/10.3389/fneur.2026.1926742},
note = {CC BY 4.0},
}
RIS
TY - JOUR
TI - Independent external validation of the foramen magnum meningioma risk score: limited discrimination and overestimation of absolute risk
AU - Nafiye Sanlier
AU - Umid Sulaimanov
AU - Ufuk Erginoglu
AU - Behman Demir
AU - Ahmed Rasim Bayramoglu
AU - Mariagrazia Nizzola
AU - Abdullah Keles
AU - Mustafa K. Baskaya
PY - 2026
DA - 2026/10/23
JO - Frontiers in Neurology
DO - 10.3389/fneur.2026.1926742
UR - https://doi.org/10.3389/fneur.2026.1926742
AB - ObjectiveForamen magnum meningiomas (FMMs) cause substantial operative morbidity because of their close relationship to the brainstem, lower cranial nerves, vertebral artery (VA), and upper cervical spinal cord. The Foramen Magnum Meningioma Risk Score (FMMRS) is the only published preoperative, MRI-based model for estimating postoperative complication risk. However, it has not been independently validated, and its calibration is unknown. We performed independent external validation, focusing on absolute risk transportability.MethodsIn this single-center, retrospective study, 40 consecutive adults who underwent microsurgical FMM resection were analyzed. The FMMRS was recalculated de novo from preoperative MRI by a neurosurgeon blinded to outcomes, with independent re-scoring by a second neurosurgeon. The primary outcome was any postoperative complications; a major complication was a prespecified secondary outcome. Discrimination was assessed using the area under the receiver operating characteristic curve (AUC) and calibrated the primary outcome using the calibration slope and intercept, the Brier score, and observed-vs-expected rates across the published risk groups.ResultsComplications occurred in 14/40 patients (35.0%) with major complications in 7/40 (17.5%). Point estimates suggested limited discrimination for both endpoints (AUCs of 0.64 [95% CI 0.46–0.79] and 0.67 [95% CI 0.48–0.84]), with confidence intervals that did not exclude chance. Observed complication rates were lower than predicted in the intermediate- and high-risk groups, indicating an overestimation of absolute risk. The calibration slope was 0.23 (95% CI − 0.04 to 0.57), the intercept −0.90 (95% CI − 1.45 to −0.57), and the Brier score (0.333) exceeded that of the null model (0.228). The largest discrepancy was in the high-risk group, where the expected rate was 96.4% vs. an observed rate of 42.9% (95% CI 21.4–67.4%). In exploratory threshold analysis, FMMRS ≥6 captured all major complications, whereas the published high-risk threshold of ≥8 missed approximately half.ConclusionIn this independent external cohort, the FMMRS retained only limited value as an ordinal stratifier for complication risk and overestimated absolute complication probabilities, particularly for high-risk patients. Its published probabilities should not guide individualized preoperative counseling without recalibration; larger multicenter studies with patient-level data are needed to refine and validate a clinically reliable preoperative prediction model.
SN - 1664-2295
ER -