The tentorial angle is measured between a line connecting the nasion with the tuberculum sellae and the the angle of the straight sinus. Normally it should measure between 27 and 52 degrees.
Abnormalities of the posterior fossa / base of skull can alter this. For example this angle is elevated in achondroplasia.
- 1. Kao SC, Waziri MH, Smith WL et-al. MR imaging of the craniovertebral junction, cranium, and brain in children with achondroplasia. AJR Am J Roentgenol. 1989;153 (3): 565-9. doi:10.2214/ajr.153.3.565 - Pubmed citation