Neuroanatomical MRI study: reference values for the measurements of brainstem, cerebellar vermis, and peduncles

Abstract

Objectives: To set age-specific normal reference values for brainstem, cerebellar vermis, and peduncles measurements and characterize values' variations according to gender, age, and age by gender interaction.

Methods: 565 normal brain magnetic resonance examinations with normal anatomy and signal intensity of the supra- and infratentorial structures were categorized into six age groups (infant, child, adolescent, young adult, middle-age adult, and old aged adults). Patients with congenital malformations, gross pathology of the supra- or infratentorial brain, brain volume loss, developmental delay, metabolic disorders, and neuropsychological disorders (n = 2.839) were excluded. On midsagittal T₁ weighted and axial T₂ weighted images specific linear diameters and ratios of the brainstem, cerebellar vermis, and peduncles were attained. Two observers assessed a random sample of 100 subjects to evaluate the inter- and intraobserver reproducibility. Intraclass correlation coefficients, means ± standard deviation, one and two-way analysis of variance tests were used in the statistical analysis.

Results: Good to excellent inter- and intraobserver measurements' reproducibility were observed, except for the transverse diameter of the midbrain, the anteroposterior diameter of the medulla oblongata at the pontomedullary and cervicomedullary junctions, cerebellar vermis anteroposterior diameter, and thickness of the superior cerebellar peduncle. Age-specific mean values of the investigated measurements were established. A significant gender-related variation was recorded in the anteroposterior diameter of the basis pontis (p = 0.044), the anteroposterior diameter of the medulla oblongata at the cervicomedullary junction (p = 0.044), and cerebellar vermis height (p = 0.018). A significant age-related change was detected in all measurements except the tectal ratio. Age by gender interaction had a statistically significant effect on the tectal ratio, inferior, and middle cerebellar peduncles' thickness (p = 0.001, 0.022, and 0.028, respectively).

Conclusion: This study provides age-specific normal mean values for various linear dimensions and ratios of the posterior fossa structures with documentation of measurements' variability according to gender, age, and their interaction.

Advances in knowledge: It provides a valuable reference in the clinical practice for easier differentiation between physiological and pathological conditions of the posterior fossa structures especially various neurodegenerative diseases and congenital anomalies.

Figure 1.

MRI mid-sagittal non-enhanced T₁WI. (a) demonstrates the modification of Oba’s method for midbrain and pons segmentation via four demarcating lines (I, II, III, and IV), line I representing the upper boundary of the midbrain connecting the mammillary body anteriorly to the superior boundary of the quadrigeminal plate posteriorly, line II separating between midbrain and pons, connecting superior pontine notch anteriorly to the inferior boundary of the quadrigeminal plate posteriorly, line III separating pons and medulla oblongata, drawn parallel to line II passing through the inferior pontine notch. Addition of line IV as a demarcation of the medullocervical junction drawn parallel to line III at the level of the foramen magnum. (b) demonstrates the vertical measurements, including line I for the vertical diameter of the tectum, line II for the vertical diameter of the midbrain, line III for the vertical diameter of the pons, line IV for cerebellar vermis height. (c) demonstrates the AP measurements as follows: line I for AP diameter of the tectum, line II for AP diameter of the midbrain, line III AP diameter of the basis pontis, line IV for AP diameter of the pons, line V for cerebellar vermis AP diameter. AP, anteroposterior; T₂WI, T₂weighted imaging.

Figure 2.

MRI axial T₂WI. (a) Dotted line expresses the transverse diameter of the midbrain, star points to the level of the superior colliculus. (b) Black arrow points to the line that expresses the thickness of the superior cerebellar peduncle, white arrow points to the level of the inferior colliculus. (c) Line expresses the transverse diameter of the pons, the dotted line refers to the thickness of the middle cerebellar peduncle, arrow points to the trigeminal nerve. (d) Black line refers to the transverse diameter of the medulla oblongata, black arrows point to the inferior olivary nucleus. (e) Black line refers to the thickness of the inferior cerebellar peduncle.