Meningioma Risk Score Overestimates Surgical Complications in Independent Validation

Foramen magnum meningiomas are among the most technically demanding tumors in neurosurgery. Because they arise at the skull base, they sit in immediate proximity to the brainstem, the lower cranial nerves, the vertebral artery, and the upper cervical spinal cord, and operations in this region carry substantial morbidity. To help surgeons weigh those risks before an operation, researchers previously developed the Foramen Magnum Meningioma Risk Score, or FMMRS, a preoperative model built from MRI features that estimates the likelihood of postoperative complications. Until now, however, the score had never been independently validated, and nothing was known about how well its predicted probabilities matched real-world outcomes.

A new single-center, retrospective study set out to test exactly that. The researchers analyzed 40 consecutive adults who underwent microsurgical resection of a foramen magnum meningioma. A neurosurgeon who was blinded to the patients’ outcomes recalculated the FMMRS from scratch using the preoperative MRI scans, and a second neurosurgeon independently re-scored the same images to check consistency. The primary outcome was any postoperative complication, with major complications as a prespecified secondary endpoint. The team then evaluated how well the score distinguished patients who had complications from those who did not, using the area under the receiver operating characteristic curve, and how well its absolute predictions matched observed rates, using the calibration slope and intercept, the Brier score, and a comparison of observed versus expected rates across the published risk groups.

Complications occurred in 14 of the 40 patients, or 35.0 percent, and major complications in 7 of 40, or 17.5 percent. The point estimates for discrimination were modest: an AUC of 0.64 for any complication and 0.67 for major complications, with confidence intervals that did not exclude chance performance. In practical terms, the score’s ability to separate higher-risk from lower-risk patients was limited in this independent cohort.

The calibration findings were more striking. Observed complication rates came in well below the probabilities the published model predicted in both the intermediate- and high-risk groups, indicating a systematic overestimation of absolute risk. The calibration slope was 0.23 and the intercept was −0.90, both signaling poor agreement between predicted and observed probabilities. The Brier score of 0.333 was worse than the 0.228 achieved by a null model that ignores the score altogether. The largest gap appeared in the high-risk group, where the model expected complications in 96.4 percent of patients but they actually occurred in 42.9 percent.

An exploratory threshold analysis added a further caveat. A cutoff of FMMRS at 6 or higher captured all major complications in this cohort, whereas the published high-risk threshold of 8 or higher missed roughly half of them. The authors conclude that, in this independent external cohort, the FMMRS retained only limited value as an ordinal stratifier of complication risk and overestimated absolute complication probabilities, particularly for patients classified as high risk. They caution that the published probabilities should not be used to guide individualized preoperative counseling without recalibration, and they call for larger multicenter studies with patient-level data to refine and validate a clinically reliable preoperative prediction model for this operation.

Subject of Research: Independent external validation of a preoperative MRI-based risk score for predicting complications after foramen magnum meningioma surgery

Article Title: Independent external validation of the foramen magnum meningioma risk score: limited discrimination and overestimation of absolute risk

Article References: Sanlier, N., Sulaimanov, U., Erginoglu, U., Demir, B., Bayramoglu, A. R., Nizzola, M., Keles, A., & Baskaya, M. K. (2026). Independent external validation of the foramen magnum meningioma risk score: limited discrimination and overestimation of absolute risk. Frontiers in Neurology, 17, Article 1926742. https://doi.org/10.3389/fneur.2026.1926742

Image Credits: AI Generated

DOI: 10.3389/fneur.2026.1926742

Keywords: foramen magnum meningioma, risk score, external validation, calibration, discrimination, neurosurgery, skull base, postoperative complications, MRI, prediction model, Brier score, Independent