Morphometric Analysis of the Foramen Magnum and Its Application in Sex Estimation: A Combined Dry Skull and Computed Tomographic Study in a Central Indian Population

Abstract

Background: The foramen magnum (FM) exhibits population-specific sexual dimorphism of established forensic value, but classification accuracy reported across populations varies widely and no dedicated morphometric database exists for the Central Indian population.

Objective: To establish population-specific FM morphometric norms and evaluate their utility for sex estimation using a cross-validated statistical approach.

Methods: A cross-sectional study of 220 specimens (110 dry adult skulls, 110 head CT scans; 110 male, 110 female) measured FM anteroposterior diameter (APD), transverse diameter (TD), circumference, area, index, and shape morphotype using a digital vernier calliper and DICOM multiplanar reconstruction respectively. Sex differences were tested by Welch's t-test/Mann-Whitney U as appropriate; sex classification used multivariable logistic regression evaluated by leave-one-out cross-validation (LOO-CV).

Results: Mean FM APD was 33.80±2.80 mm and TD 29.06±2.26 mm. Males exceeded females on APD, TD, circumference and area (all p<0.05); the FM index did not differ by sex (p=0.856). The oval morphotype predominated (44.1%). A four-parameter logistic model classified sex with 69.1% LOO-CV accuracy (AUC=0.762), comparable to similarly cross-validated figures in the international literature.

Conclusion: FM morphometry is significantly sexually dimorphic in this population and provides a supportive, cross-validated tool for forensic sex estimation, though not a stand-alone method.