Computed Tomography-Based Morphology and Morphometry of the Foramen Magnum and Their Associations With Sex and Age: A Cross-Sectional Study

BackgroundForamen magnum (FM) morphology and dimensions matter in craniovertebral junction surgery and forensic sex estimation; however, computed tomography (CT) data from Gujarat, western India, are scarce.The primary aim was to compare FM diameters between men and women; secondary aims were to describe FM shape and examine the associations of shape and FM measurements with sex and age. Materials and methodsThis cross-sectional CT study analyzed 100 adults (50 men and 50 women) aged 18-55 years who were recruited using sex-stratified quota sampling.FM shape was classified into eight categories, and anteroposterior (AP) and transverse (TD) diameters were measured; estimated area and FM index were derived.Sex-and age-related associations were analyzed using Welch t-tests with 95% confidence intervals (CIs) and Holm correction, sex-adjusted regression of continuous age, and Fisher-Freeman-Halton exact tests.Intraobserver and interobserver reliability were assessed using 20 participant-linked repeat-reading records (10 per sex). ResultsHexagonal (24%), oval (19%), and irregular (15%) were the most common FM outlines.No statistically significant shape association was detected between sex (exact p = 0.509) and age group (p = 0.162).Men had larger AP diameters (mean difference: 2.04 mm, 95% CI: 0.93-3.14),TD (2.11 mm, 1.18-3.04),and estimated area (103.3 mm², 60.9-145.8;Holm-adjusted p < 0.001 for each).The FM index was not significantly different (p = 0.409).No statistically significant age effect was detected.In 20 linked scans, intraobserver and interobserver shape agreement was 90% (κ = 0.882) and 80% (κ = 0.763), respectively; absolute-agreement intraclass correlation coefficients (ICCs) for the diameters ranged from 0.989 to 0.998.The originally unusual TD > AP measurements for participant 27 were similar on both repeats, and all readings were labeled as FM pentagonal. ConclusionsIn this single-center sample, FM linear dimensions and estimated area were greater in men.Shape, index, and age comparisons were not significant, although modest associations cannot be excluded.Repeat readings showed strong within-sample observer agreement, and independent Digital Imaging and Communications in Medicine (DICOM) review confirmed the unusual wider-than-long FM without an identified osseous abnormality.The native axial measurement plane remains a limitation.The descriptive findings do not establish a validated forensic sex-estimation method.