Morphological Types of Foramen Magnum

Introduction: The foramen magnum (FM) is a unique and complex anatomical area located in the central basal region of the occipital bone. It is a three-dimensional opening through which vital structures pass, such as the medulla oblongata and its membranes, the spinal accessory nerve, the vertebral arteries, the anterior and posterior spinal arteries, the tectorial membrane and the alar ligaments. Because of this vital relationship between the FM and its content, it is of great importance to study the morphological types of FM. Findings from such evaluations have essential applications in clinical practice and in surgery.
Objective: To determine the incidence of different morphological types of FM.
Materials and Methods: 110 FM from dry human crania of known sex and age were analyzed. The specimens belong to the anatomical collections of Tiradentes University (UNIT) and the Metropolitan University of Education and Culture (UNIME). Among these, 66 were male, 44 were female and their ages ranged from 11 to 91 years (mean: 58.01 years). FM morphology was studied using photographic images and with the aid of Corel Draw Photo-Paint X5.
Results: Among the 110 FM analyzed, nine morphological types were found: pear-shaped 37.27%, rounded 15.45%, tetragonal 10.91%, biconvex 10.91%, hexagonal 9.09%, oval 5.45%, pentagonal 2.73% and heptagonal 1.82%. In the remaining 6.36% of the FM, it was not possible to define a regular and specific form.
Conclusions: Pear-shaped FM predominated, followed by rounded FM. In relation to sex, the tetragonal and biconvex forms occurred five times more frequently in males than in females, while the hexagonal form occurred twice as frequently in females than in males.