Prenatal development of cranial base in normal Korean fetuses

Background: The cranial base is not only an end result of complex segmental growth of rostral end of axial skeleton but also has a tremendous impact on the development of the brain and facial structure. However, little is known about the method for the systematic analysis of the shape of the cranial base in the developing human fetus. We used roentgenograms of the cranial base and eviscerated bones for the assessment of the development of the cranial bony complex. Methods: The cranial base was removed from 64 normal human fetuses after 18-40 weeks of gestation. Roentgenograms were taken perpendicular to the cranial base. Major anatomical landmarks are defined as follows: the center of pituitary fossa of sphenoid bone (point S), the growth center of zygomatic bone, the anterior point of nasal septum, otic cartilage, and anterior and posterior growth centers of maxilla. The anterior cranial base angle, the middle cranial base angle, the posterior cranial base angle, the maxillary trapezoid area, the horizontal middle face area, and the occipital cranial base triangle area are defined from the landmarks, and the growth of each parameter was analyzed by gestational age. Results: The proportional growth of the anterior, middle, and posterior cranial fossae could be assessed by the angles around the center of the pituitary fossa (point S) and by the anterior, middle, and posterior cranial base angles. The anterior cranial base angle was relatively constant during the fetal period at 107.4-112.5°, whereas the middle cranial base angle gradually increased, and the posterior cranial base angle decreased. With increasing gestational age, the horizontal middle face area increased rapidly, in contrast to those of the maxillary trapezoid area, occipital cranial base triangle area, or foramen magnum area. Conclusions: The important keys in the structural development of the normal human cranial base are anterior, middle, and posterior cranial base angles. We could define the developmental pattern of human cranial base, which in turn provides a model of a standard growth pattern applicable to the study of the different malformations in the craniofacial structure.