Angle between vein of Galen and straight sinus: a novel marker on microvascular flow imaging for prenatal assessment of tentorium cerebelli position.

Objectives: Posterior fossa anomalies (PFAs) are associated with a wide spectrum of neurodevelopmental disabilities, with presentation ranging from no obvious clinical symptoms to severe neurodevelopmental delay. The differential diagnosis of fetal PFAs using imaging is crucial for prenatal counseling and prognostic evaluation. Imaging of the tentorium cerebelli (TC) is critical for the differential diagnosis of fetal PFAs; however, achieving this using prenatal grayscale ultrasound is challenging. This study aimed to establish a reference range for a new measurement, the angle between the vein of Galen and the straight sinus (AVGS), measured using microvascular flow imaging, and to evaluate prospectively the effectiveness of AVGS for assessment of the position of the fetal TC.

Methods: This was a single-center prospective validation study including singleton pregnancies examined between 16 and 38 gestational weeks at Beijing Obstetrics and Gynecology Hospital, Capital Medical University, Beijing Maternal and Child Health Care Hospital, between January 2022 and July 2023. AVGS was measured in normal fetuses and used to establish a reference range. AVGS was then used to predict prospectively the position of the TC in 50 fetuses with one or more intracranial malformations, using cut-offs of ≤ 5^th centile or ≥ 95^th centile to define abnormal AVGS. All intracranial malformations and the position of the TC in these fetuses were confirmed using fetal brain magnetic resonance imaging. The sensitivity, specificity, positive and negative predictive values and likelihood ratios were calculated to assess the performance of AVGS in the prediction of abnormal position of the fetal TC.

Results: The study group comprised 602 singleton pregnancies, including 522 normal fetuses and 50 fetuses with an intracranial anomaly. A reference range for fetal AVGS was established. Fetal AVGS decreased with advancing gestational age. Ten of the 50 fetuses with an intracranial anomaly had an abnormally positioned TC. The sensitivity and specificity of AVGS for the prediction of abnormal position of the TC in fetuses with an intracranial malformation were 90.0% (95% CI, 71.4-100.0%) and 95.0% (95% CI, 88.2-100.0%), respectively. The positive and negative predictive values were 81.8% (95% CI, 47.8-96.8%) and 97.4% (95% CI, 84.9-99.9%), respectively, and the positive and negative likelihood ratios were 18.000 (95% CI, 4.590-70.592) and 0.105 (95% CI, 0.016-0.677), respectively.

Conclusions: AVGS is a new and useful marker for the prenatal evaluation of fetal TC position. Increased AVGS (≥ 95^th centile) suggests an abnormally elevated position of the TC, while decreased AVGS (≤ 5^th centile) suggests an abnormally low TC. AVGS is helpful for differential diagnosis in fetuses with PFA and can inform appropriate prenatal counseling. © 2024 International Society of Ultrasound in Obstetrics and Gynecology.