Tegmentovermian angle

Last revised by Dr Rohit Sharma on 22 Oct 2022

The tegmentovermian 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 brainstem 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° and an elevated angle is often associated with posterior fossa malformations 1,2:

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