The human skull base angle during the second trimester of gestation.

In an attempt to demonstrate and explain the radiographic findings and changes in the skull base angle (SBA) during the second trimester of gestation, we examined 26 human fetal heads of 15-25 weeks gestational age by direct sagittal and axial high resolution computed tomography. The fetuses were preserved in 10% formalin. On magnified sagittal tomograms tracings of the skull base were made and three anatomical landmarks (nasion, sella turcica and the lowest part of the clivus) were used to define the SBA formed between them. The changes in the SBA during the second trimester were related to the gestational age of the fetuses. We found a significant increase of the SBA, of approximately 27 degrees, during the second trimester of gestation. This is different from previous measurements.