Automated Quantitation of Spinal CSF Volume and Measurement of Craniospinal CSF Redistribution following Lumbar Withdrawal in Idiopathic Intracranial Hypertension

Abstract

Background and purpose: Automated methods for quantitation of tissue and CSF volumes by MR imaging are available for the cranial but not the spinal compartment. We developed an iterative method for delineation of the spinal CSF spaces for automated measurements of CSF and cord volumes and applied it to study craniospinal CSF redistribution following lumbar withdrawal in patients with idiopathic intracranial hypertension.

Materials and methods: MR imaging data were obtained from 2 healthy subjects and 8 patients with idiopathic intracranial hypertension who were scanned before, immediately after, and 2 weeks after diagnostic lumbar puncture. Imaging included T1-weighted and T2-weighted sequences of the brain and T2-weighted scans of the spine. Repeat scans in 4 subjects were used to assess measurement reproducibility. Whole CNS CSF volumes measured prior to and following lumbar puncture were compared with the withdrawn amounts of CSF.

Results: CSF and cord volume measurements were highly reproducible with mean variabilities of -0.7% ± 1.4% and -0.7% ± 1.0%, respectively. Mean spinal CSF volume was 77.5 ± 8.4 mL. The imaging-based pre- to post-CSF volume differences were consistently smaller and strongly correlated with the amounts removed (R = 0.86, P = .006), primarily from the lumbosacral region. These differences are explained by net CSF formation of 0.41 ± 0.18 mL/min between withdrawal and imaging.

Conclusions: Automated measurements of the craniospinal CSF redistribution following lumbar withdrawal in idiopathic intracranial hypertension reveal that the drop in intracranial pressure following lumbar puncture is primarily related to the increase in spinal compliance and not cranial compliance due to the reduced spinal CSF volume and the nearly unchanged cranial CSF volume.

Fig 1.

Flow chart of the CSF segmentation method. T1- and T2-weighted brain images are used to obtain the ventricular and intracranial CSF volumes by using publicly available software packages. Spinal CSF and cord volumes are obtained using the 3 T2-weighted scans with a custom-developed software.

Fig 2.

A mid-sagittal image demonstrating complete coverage of the CNS generated by merging 3 separate acquisitions (A) with overlapping coverage indicated by red bars on the left. B, Segmentation of cranial (blue), ventricular (yellow), and spinal (red) CSF and cord (green).

Fig 3.

Sample CSF (red outline) and cord (green) segmentations along the spinal column at the level of C3, C7, T6, T10, L2, and L5 vertebrae.

Fig 4.

Average CSF cross-sectional area before and after lumbar puncture (A) and average change in CSF cross-sectional area following CSF withdrawal with respect to the distance from the foramen magnum to the caudal end of the thecal sac (B).

Fig 5.

The relationship between the CSF volume withdrawn during lumbar puncture and CSF volume change in the spinal canal between the pre- and post-lumbar puncture scan (A) and the pre- and the 2-week follow-up scan (B) as measured by the proposed method.