Morphometric Analysis of the Foramen Magnum in a Brazilian Population

Abstract

The foramen magnum is an opening located at the base of the skull, more specifically in the occipital bone, and it has a remarkable anatomical significance, as many important structures, such as nerves, arteries and the medulla oblongata, pass through it. A small, large or asymmetric foramen magnum can end up causing clinical complications, such as compression, or increasing the risk of herniation. By becoming aware of the most frequent sizes and shapes in the population, it also becomes easier to detect diseases that change its morphology, such as achondroplasia, which makes it smaller, and Chiari I and II malformations, which makes it larger. In this study, we aim to observe gender‐related anatomical differences of the foramen magnum and report the frequency of the most commonly observed shapes. To achieve this, we studied the morphometry of the foramen magnum in 40 skulls. Anteroposterior and transverse length measurements were manually obtained with the aid of a digital caliper. Digital images were used to analyze the shapes of each available foramen magnum, which were then subdivided according to the following categories: oval, diamond, hexagon, egg‐shaped, pentagon and round. The differentiation between male and female was based on sexual dimorphism, using anatomical landmarks as a reference. The results obtained showed that among the 40 skulls observed, 32 were male and 8 were female. Our study revealed a statistically significant (p=0.0462) sex‐related difference between the anteroposterior diameters of the foramina, which is often larger in men and smaller in women. In contrast, the transverse diameter was not statistically significant. As for the shapes, 39 were analyzed: 12 (30.76%) of them in oval shape, 10 (25.64%) in diamond shape, 8 (20.51%) in hexagon shape, 4 (10.25%) in egg shape, 3 (7.69%) in pentagon shape and 2 (5.12%) in round shape. Therefore, we conclude that the anteroposterior length of the foramen magnum can be used as a tool to help differentiate between skulls of different sexes for academic and forensic purposes. Knowledge of the most common possible shapes for the foramen magnum can also be an important predictor, useful for clinical and anatomical knowledge. The data obtained has potential use in forensic techniques, in addition to providing information on variations in the Brazilian population.