Threshold Selection Criteria for Quantification of Lumbosacral Cerebrospinal Fluid and Root Volumes from MRI

Correlation between individual physical characteristics and spinal cerebrospinal fluid volume

Spinal cerebrospinal fluid (CSF) volume is the primary determinant for the spread of spinal anesthesia. However, it cannot generally be obtained during spinal anesthesia, and patient physical characteristics are always adopted to obtain a suitable spinal spread. In this study, we sought to explore the relationship between individual physical characteristics and thoracosacral CSF volume to provide a theoretical basis for more accurate spinal anesthesia. In total 35 healthy volunteers were enrolled in this study. Three-dimensional magnetic resonance imaging was used to reconstruct and measure the spinal CSF volume. Physical characteristics and spinal CSF volume were recorded. Bivariate and multiple linear regression analyses were used to analyze the correlation between the individual physical characteristics and thoracosacral CSF volume. Total of 31 participants were included in the final analysis. Bivariate linear correlation analysis showed that the volume of thoracosacral CSF was correlated with both individual dorso-sacral distance and height (both p < 0.01), but not with abdominal girth (p > 0.05). Multiple linear regression analyses revealed that the adjusted R² values were 0.404 for the regression equation between thoracosacral CSF volume, dorso-sacral distance, and abdominal girth. Our study showed that dorso-sacral distance and abdominal girth were essential factors contributing to thoracosacral CSF volume. A longer dorso-sacral distance and smaller abdominal girth mean larger spinal CSF volume.

Microanatomy Relevant to Intrathecal Drug Delivery

This chapter describes the microanatomy of the spinal cord that is relevant to intrathecal drug delivery started with covering of the spinal cord that are pierced to enter the intrathecal space. The dural sac is mostly constituted by the outer layer of dura and the inner layer called arachnoid membrane, which regulates diffusion of drugs into the intrathecal space. The pia matter surrounding the spinal cord is a permeable structure allowing the passage of drugs through intercellular spaces. The relationship between nerve roots, CSF, and subarachnoid catheters determines the passage of an intrathecal catheter which can cause damage to nerve roots and spinal cord. Multiple factors may be involved in the mechanisms of drug diffusion across the membranes of the spinal cord, as well as in their dilution with the CSF, which will lead to the final drug distribution and availability at nerve roots and the spinal cord.

Abdominal girth and dorso-sacral distance can be used to estimate lumbosacral cerebral fluid volume

BACKGROUND

Patients' abdominal girth and vertebral column length are highly correlated with the spread of local anaesthetics after spinal anaesthesia. Lumbosacral cerebrospinal fluid volume is the primary determinant for spinal spread. Thus, we attempted to verify the hypothesis that abdominal girth and dorso-sacral distance are correlated with lumbosacral cerebrospinal fluid volume.

METHODS

Forty-five healthy volunteers were enrolled in this study to measure lumbosacral cerebrospinal fluid volume using magnetic resonance imaging. The age, height, weight, abdominal girth, dorso-sacral distance and lumbosacral cerebrospinal fluid volume of the volunteers were recorded. Multiple linear regression analysis was used to analyse the correlation between age, height, weight, abdominal girth, dorso-sacral distance and lumbosacral cerebrospinal fluid volume.

RESULTS

Two volunteers were excluded because of lumbar disc herniation, leaving 43 volunteers for analysis. Multiple linear regression analysis showed a strong correlation between abdominal girth, dorso-sacral distance and lumbosacral cerebrospinal fluid volume (both P < 0.01). The adjusted R² was 0.644. Volunteers with small abdominal girth showed clear images of cerebrospinal fluid in the nerve root cuff at the intervertebral foramen in the three-dimensional magnetic resonance imaging reconstruction of lumbosacral cerebrospinal fluid, while the images were vague in volunteers with large abdominal girth. Clearer images implied larger lumbosacral cerebrospinal fluid volume, while vaguer images, smaller lumbosacral cerebrospinal fluid volume.

CONCLUSIONS

Multiple regression analysis revealed that abdominal girth and dorso-sacral distance were correlated with lumbosacral cerebrospinal fluid volume. Smaller abdominal girths and larger dorso-sacral distances predict larger lumbosacral cerebrospinal fluid volume.

A 3D subject-specific model of the spinal subarachnoid space with anatomically realistic ventral and dorsal spinal cord nerve rootlets

BACKGROUND

The spinal subarachnoid space (SSS) has a complex 3D fluid-filled geometry with multiple levels of anatomic complexity, the most salient features being the spinal cord and dorsal and ventral nerve rootlets. An accurate anthropomorphic representation of these features is needed for development of in vitro and numerical models of cerebrospinal fluid (CSF) dynamics that can be used to inform and optimize CSF-based therapeutics.

METHODS

A subject-specific 3D model of the SSS was constructed based on high-resolution anatomic MRI. An expert operator completed manual segmentation of the CSF space with detailed consideration of the anatomy. 31 pairs of semi-idealized dorsal and ventral nerve rootlets (NR) were added to the model based on anatomic reference to the magnetic resonance (MR) imaging and cadaveric measurements in the literature. Key design criteria for each NR pair included the radicular line, descending angle, number of NR, attachment location along the spinal cord and exit through the dura mater. Model simplification and smoothing was performed to produce a final model with minimum vertices while maintaining minimum error between the original segmentation and final design. Final model geometry and hydrodynamics were characterized in terms of axial distribution of Reynolds number, Womersley number, hydraulic diameter, cross-sectional area and perimeter.

RESULTS

The final model had a total of 139,901 vertices with a total CSF volume within the SSS of 97.3 cm³. Volume of the dura mater, spinal cord and NR was 123.1, 19.9 and 5.8 cm³. Surface area of these features was 318.52, 112.2 and 232.1 cm² respectively. Maximum Reynolds number was 174.9 and average Womersley number was 9.6, likely indicating presence of a laminar inertia-dominated oscillatory CSF flow field.

CONCLUSIONS

This study details an anatomically realistic anthropomorphic 3D model of the SSS based on high-resolution MR imaging of a healthy human adult female. The model is provided for re-use under the Creative Commons Attribution-ShareAlike 4.0 International license (CC BY-SA 4.0) and can be used as a tool for development of in vitro and numerical models of CSF dynamics for design and optimization of intrathecal therapeutics.