Background and purpose: Neural structures in the posterior fossa grow at different rates during development. While there are computationally intensive approaches to analyze growth of the cerebellum and brainstem, there is a paucity of information about summary measures of normal posterior fossa development suitable for real-time clinical use. The present study investigates changes in the trajectory of the tentorium as measured by the occipital and tentorial angles at different stages of development.
Methods: A retrospective study was conducted drawing from a Boston Children's Hospital database of over 1500 magnetic resonance imaging (MRI) studies. The imaging study population included fetuses older than 20 gestational weeks and children between the ages of 0 and 10 years. Two parameters were measured for all subjects: (1) the tentorial angle (the angle between the tentorium and a line from the internal occipital protuberance to the tuberculum sellae) and (2) the occipital angle (the angle between the tentorium and a line from the internal occipital protuberance to the opisthion). Descriptive statistics were used to analyze the study cohort.
Results: We reviewed 1510 brain MRI studies, and 367 studies met the inclusion criteria (125 fetal and 242 postnatal studies). During fetal development, the inclination of the tentorium showed an ascending course, while it plateaus after birth.
Conclusions: During the second and third trimesters, the tentorial and occipital angles steadily increase reflecting the dynamic growth of the posterior fossa structures. Postnatally, the tentorial angle decreases and the tentorium slopes downward and plateaus, possibly due to stabilization of posterior fossa development and ongoing growth of the cerebrum. Together, these findings suggest that the tentorial angle can serve as an imaging biomarker of posterior fossa development during the second half of fetal life.
Keywords: Cerebellum; Fetal development; MRI; Occipital angle; Tentorial angle; Tentorium.