Body position influence on cerebrospinal fluid volume redistribution inside the cranial and spinal CSF compartments

Abstract

Introduction: It is generally accepted that during body position changes from horizontal to vertical there is a short-lasting shift of a certain CSF volume from the cranium into the hydrostatically lower parts of the spinal space, which leads to transitory CSF pressure decrease to negative values.

Methods: In order to test this, we performed MRI volumetry of cranial and spinal part of the CSF space in healthy volunteers of both genders (n = 22) in three different body positions [horizontal (H); elevated head and upper body (H-UP) under an angle about 30° from the base; elevated lower body (B-UP) under an angle about 30° from the base].

Results: Volumes of brain and spinal cord tissue did not change during body position changes. Significant CSF volume (ml) changes occur inside the spinal space in the tested body positions, primarily in the lumbosacral segment (H-UP - 38.1 ± 7.0; H - 34.4 ± 6.5; B-UP - 28.7 ± 6.5), while at the same time no significant CSF volume changes have been observed inside the cranium in two tested positions (H and B-UP) in which it was possible to measure intracranial CSF volume changes or if we sum up cervical and cranial CSF volumes in those positions.

Conclusion: Observed results suggest that during the changes of body position CSF volume redistribution occurs, primarily inside the spinal and not the cranial space. This is in accordance with the new hypothesis by which spinal intradural space can significantly change its volume due to its elasticity, thus adjusting to the influence of gravity and pressure changes.

Keywords: MR volumetry; body position; cranial CSF volume; segmentation; spinal CSF volume; volume redistribution.

Figure 1

Schematic representation of the body position during MRI imaging: (A) horizontal position (H), (B) elevated lower body position (B-UP) under the certain angle α (about 30°) in relation to the base, (C) elevated head and the upper body position (H-UP) under the certain angle β (about 30°) in relation to the base.

Figure 2

Schematic representation of the volumetric analysis process of MRI images of the brain (volBrain) and spine (ITK-SNAP). The final result of the segmentation of the spinal part (cervical-red, thoracic-green and lumbosacral-blue part) in the ITK-SNAP programme is shown in the down part of scheme.

Figure 3

Differences between the measured values of intracranial, ventricular and subarachnoid CSF volumes (ml) related to different body positions during MRI imaging. Columns represent the values of arithmetic means of intracranial, lateral ventricles and subarachnoid CSF volumes with their 95% confidence intervals in the horizontal position (H) and in the position with the elevated lower body (B-UP), while white circles and squares represent individual values of those volumes in 22 subjects. There were no statistically significant differences in intracranial, ventricular and cranial subarachnoid CSF volumes in different body positions.

Figure 4

Differences between measured values of the total spinal CSF volume (ml) related to body position during MRI imaging. Columns represent the values of arithmetic means of total spinal CSF volume with their 95% confidence intervals in horizontal position (H), in the position with elevated lower body (B-UP) and in the position with elevated head and upper body (H-UP), while white circles represent individual values of those volumes in 22 subjects. There were no statistically significant differences between the measured total spinal CSF volume in different body positions.

Figure 5

Differences between measured values of lumbosacral CSF volume (ml) related to the changes of body position during MRI imaging. Columns represent the values of arithmetic means of lumbosacral CSF volumes with their 95% confidence intervals in the horizontal position (H), in the position with the elevated lower body (B-UP) and in the position with the elevated head and upper body (H-UP), while white circles represent individual values of those volumes in 22 subjects. The analysis of variance determined significant difference between the three MRI measuring positions (p < 0.001). An additional post-hoc Bonferroni analysis showed significant differences primarily between the horizontal (H) position and the elevated lower body position (B-UP) (p = 0.016), as well as between the elevated head and upper body position (H-UP) and the elevated lower body position (B-UP) (p < 0.001).

Figure 6

Differences between measured values of total thoracic and lumbosacral CSF volume (ml) related to the changes of body position during MRI imaging. Columns represent the values of arithmetic means of the total thoracic and lumbosacral CSF volumes with their 95% confidence intervals in horizontal position (H), in the position with elevated lower body (B-UP) and in the position with elevated head and upper body (H-UP), while white circles represent individual values of those volumes in 22 subjects. A post-hoc Bonferroni analysis showed significant differences primarily between the elevated head and upper body position (H-UP) and the elevated lower body position (B-UP) (p = 0.009).