Age-Related Changes and Reference Values of Bicaudate Ratio and Sagittal Brainstem Diameters on MRI

Cranial magnetic resonance imaging (MRI) plays an important role in the diagnosis of neurometabolic diseases, and, in addition, temporal patterns of signal and volume changes allow insight into the underlying pathogenesis. While assessment of volume changes by visual inspection is subjective, volumetric approaches are often not feasible with rare neurometabolic diseases, where MRIs are often acquired with different scanners and protocols. Linear surrogate parameters of brain volume, for example, the bicaudate ratio, present a robust alternative that can be derived from standard imaging sequences. Due to the continuing postnatal brain and skull development and later brain involution, it is, however, necessary to compare patient values with age age-adapted normal values.In this article, we present age-dependent normal values derived from 993 standard scans of patients with normal MRI findings (age range: 0-80 years; mean = 19.9; median = 12.8 years) for bicaudate ratio as a measure of global supratentorial volume, as well as the maximal anteroposterior diameters of mesencephalon, pons, and medulla oblongata as parameters of brainstem volume. The provided data allow quantitative, objective assessment of brain volume changes instead of the usually performed visual and therefore subjective assessment.