Quantitative analysis of thecal sac volume and morphology as a diagnostic tool in intracranial hypotension.

Objectives/background: This study was undertaken to determine whether thecal sac volume and morphometry can be used to differentiate patients with spontaneous intracranial hypotension (SIH). The mechanisms underlying SIH appear to be multifactorial. Association with connective tissue disorders is established, suggesting that increased thecal sac compliance and volume may contribute to SIH.

Methods: This study is an observational cross-sectional study that used magnetic resonance imaging (MRI) to compare thecal sac volume between patients with SIH and healthy controls. Patients with SIH and matched controls were prospectively recruited from December 1, 2020 to March 1, 2022. All participants underwent volumetric MRI of the entire spine. Semiautomated segmentation was used to extract three-dimensional volumetric models of the thecal sac. A single average thecal sac model was created for each group. Signed model to model distance function was used to compute and visualize the correspondent vectors that quantify the localized differences, including shape, between control and SIH thecal sacs.

Results: Twenty-eight patients with SIH (mean age = 45.9 years, mean body mass index = 27.7, 57% male) and 28 controls (mean age = 44.4 years, mean body mass index = 26.8, 57% male) were recruited. The thecal sac was significantly larger in patients with SIH (mean = 131.7 cm³, 95% confidence interval [CI] = 108.1-155.3) than controls (mean = 116.5 cm³, 95% CI = 105.1-127.9, p < 0.001). Thecal sac volume demonstrated excellent discrimination for SIH (area under the curve = 0.91, 95% CI = 0.83-0.98, p < 0.001). Volume > 122 cm³ was 82% sensitive and 82% specific for SIH; volume > 126 cm³ was 100% specific. Regional thoracic volume was slightly higher in patients with SIH (61.6 and 57.8 cm³, respectively, p = 0.020), and lumbar volume was notably higher (46.6 and 33.0 cm³, respectively, p < 0.001).

Conclusion: Patients with SIH have a significantly larger thecal sac than controls, which can be an effective tool to diagnose these patients.