The Tegmento-vermian angle is an important measurable parameter in the assessment of posterior fossa abnormalities in the fetus. The angle is constructed on midsagittal images of the fetal brain, ideally on MRI.
The angle is formed by the intersection of the following two lines 1:
- line 1: along the dorsal surface of the brain stem parallel to the tegmentum and which should transect the nucleus gracilis at the obex.
- line 2: along the ventral surface of the vermis.
Normally the angle is close to 0 degrees and an elevated angle is often associated with posterior fossa malformations 1,2.