Posterior cranial fossa measurements taken from the midline of a sagittal, T1-weighted MRI. A1 to A5 shown in red indicate the regions in which area was estimated. Additional measurements not explicitly labeled include (a) basal angle (BASAL_ANG), (b) boogaard angle (BOOG_ANG), (c) occipital angle (OCC_ANG), (d) tentorial angle (TENT_ANG), (e) basion to reference (BASTOREF), (f) opisthion to reference (OPISTOREF), (g) trapezoid height (TRAPHEIGHT), and (h) tentorium to reference (TENTTOREF). Abbreviations: TENT_OPEN = tentorial opening, TENT = tentorium, OCC = supraoccipital bone, FM = foramen magnum, PFH = posterior fossa height, and HERN = cerebellar tonsillar herniation. This figure is reproduced from , a Wiley publication.