Semi-Fowler Position MRI in Suspected Cerebrospinal Fluid Hypovolemia: A Prospective Exploratory Feasibility Study.

OBJECTIVE: To explore the feasibility of Semi-Fowler Position MRI for visualizing posture-dependent lumbosacral dural sac changes within the same individual. METHODS: This prospective single-center study enrolled 20 patients with suspected CSF hypovolemia and 10 healthy volunteers as controls. Participants underwent whole-spine MRI in the conventional supine and mildly head-elevated Semi-Fowler positions during the same imaging session. Three blinded neurosurgeons independently evaluated posture-dependent morphological changes of the lumbosacral dural sac. The patient group was defined by clinical suspicion, and the controls did not undergo reference-standard testing to exclude spinal CSF leakage. Two patients were excluded from image analysis. RESULTS: Eighteen patients and 10 controls were analyzed. Positive ratings were assigned in both groups (patients vs controls: Reviewer A, 3/18 vs 1/10; Reviewer B, 10/18 vs 6/10; Reviewer C, 10/18 vs 5/10), demonstrating substantial overlap. Interobserver agreement was fair (Fleiss' κ = 0.344 when indeterminate ratings were excluded and κ = 0.225 when included). The findings were summarized descriptively and were not used to estimate diagnostic sensitivity or specificity. CONCLUSIONS: Semi-Fowler Position MRI demonstrated the feasibility of visualizing posture-dependent lumbosacral dural sac changes within the same individual. However, substantial overlap between the groups and only fair interobserver agreement preclude conclusions regarding group discrimination, diagnostic performance, or clinical utility. Further studies using standardized positioning, objective criteria, and independently characterized cohorts are needed to determine the clinical significance of these findings and their relationship to CSF hypovolemia or spinal CSF leakage.