Detection of sexual dimorphism of the foramen magnum in cats using computed tomography

The foramen magnum is a large round or oval opening surrounded by parts of the occipital bone. It connects the cranial cavity with the vertebral canal. The foramen magnum is an important structure having various applications in veterinary practice and forensic medicine. The variability of its shape and sexual dimorphism allow it to be exploited for sex and age identification in different species. This retrospective study used computed tomographic (CT) images of the caudal region of the 102 mixed-breed cat heads (55 males and 47 females). Eight linear measurements of the foramen magnum (FM) and occipital condyles were performed on CT images. The aim of the study was to find out if the linear measurements of the CT images of the foramen magnum showed variability between the sexes of the cats. In general, the values of the linear measurements in male cats were higher than in females. The mean maximum length of the foramen magnum (MLFM) was 11.18 ± 0.84 mm and 10.63 ± 0.72 mm in male and female cats, respectively. The mean maximum internal width of the foramen magnum (MWFM) was 14.43 ± 0.72 mm in males and 13.75 ± 1.01 mm in females. The difference between FM measurements in female and male cats was statistically significant (p value; FML: 0.001, FMW: 0.000). The MLFM confidence interval was 10.41 mm to 10.86 mm in female cats and 10.97 mm to 11.39 mm in males. The confidence interval of MWFM was 13.5 mm to 14.0 mm in female cats and 14.2 mm to 14.66 mm in male cats. With these intervals, we can predict the probability of sex in cats with 95% confidence. It was noted that measurements of the occipital condyles were not sex-determining. The difference in foramen magnum index in female and male cats was statistically insignificant (p value; 0.875). As a result of the study, it was seen that the linear measurements of the foramen magnum were sex-determining.