Flat skull base is a congenital developmental malformation of the skull base that is often combined with other congenital developmental malformations such as depression of the skull base, reduced volume of the posterior cranial fossa, and atlantoaxial dislocation. Flat skull base is diagnosed by measuring the angle of the skull base on lateral bone films. On the lateral skull film, two lines are first made, one from the root of the nose to the center of the pterygoid saddle, and one from the center of the pterygoid saddle to the anterior border of the occipital foramen magnum. The angle formed by these two lines is between 109-145 degrees in normal adults. If the angle formed by these two lines is greater than 145 degrees, the diagnosis is flat skull base.