"Twining's line, also known as the tuberculum torcula line, is a midline measurement used in the volumetric assessment of the posterior cranial fossa and of particular relevance in Chiari 1 malformations 1. The angle between the line and the tentorium is also used for similar purposes 1. It has also been used to describe mass effect in the posterior cranial fossa due to cerebellar infarction 2. This line also used as a reference for normal upper border of fourth ventricle."
"Basilar invagination can be assessed with the Klaus height index which is the perpendicular distance between Twining's line and the tip of the dens of C2."
"On the midsagittal CT or MRI image, Twining's line is the distance from the tuberculum sellae to the torcula."