The Vermian-Crest Angle: A New Method to Assess Fetal Vermis Position within the Posterior Fossa Using 3-Dimensional Multiplanar Sonography

Background: Normal morphometry of the vermis and its relation to the posterior fossa (PF) rule out most major anomalies of the cerebellum. However, accurate categorization of the position and size of the fetal vermis remains a challenge. Objective: Our aim was to test a new method to assess the position and size of fetal vermis on 3-dimensional ultrasound (3D-US). Methods: We measured the vermian-crest angle (VCA) in normal fetuses using multiplanar 3D-US. We also assessed the diameters (superoinferior, anteroposterior, and horizontal) and volume of the vermis. The Spearman rank test and linear and polynomial regression analyses were used for statistical purposes. Results: We included 126 fetuses. Mean ± SD gestational age (GA) was 26.3 ± 4.6 (range 17–35.5) weeks. Mean ± SD superoinferior, anteroposterior, and horizontal diameters were 16.2 ± 4.9, 11.2 ± 3.6, and 5.6 ± 1.6 mm, respectively. Median (range) vermian volume was 0.50 (0.05–2.9) cm 3 . The VCA was 64.49° ± 11.45. We found no correlation between GA and VCA (r = 0.15; p = 0.13), a linear correlation between GA and vermian diameters, and a quadratic correlation between GA and vermian volume. Conclusions: We provide a new method to assess vermian position and size within the PF using 3D-US. The combined information may be of value for screening purposes, particularly to differentiate between the various pathological situations encountered within the PF.