Three-dimensional analysis of foramen magnum and its adjacent structures.

The goal of this effort is to evaluate the anatomy of the foramen magnum (FM) using 3-dimensional computed tomography (3D CT), and determine whether or not the anatomical features of vascular structures and condylar foramen (CF) affect the types of FM.The CT angiography records of 101 patients (44 men and 57 women) were retrospectively examined in this study. Details of the FM, CF, and the vertebral and basilar arteries were examined using maximum intensity projection and 3D rendering images. The average age of the 101 patients was 45.28 ± 16.3 years. The 8 types of FM, in order of their frequency of occurrence, are as follows: round (19 cases; 18.8%), 2 semicircles (18; 17.8%), egg-shaped (15; 14.9%), hexagonal (14; 13.9%), tetragonal (11; 10.9%), oval (11; 10.9%), pentagonal (9; 8.9%), and irregular (4; 4%). There was no statistically significant relationship between the anatomical features of the vertebral and basilar arteries and the CF with the different types of FM (P ≥ 0.05). In our study, the diameter of the anteroposterior (AP) FM was 34.7 ± 3.6 mm, and the transverse (T) diameter was 29.5 ± 2.5 mm. The AP and T diameters were significantly higher in men than in women (P = 0.006 and P ≤ 0.001, respectively).Our study revealed that 3D CT is a safe and easy method for visualizing the anatomical structure of the FM and neighboring structures. Furthermore, this study was the first to demonstrate that there is no correlation between the 8 types of FM and the vertebral artery, basilar artery, and CF.