Three-dimensional MR volumetric analysis of the posterior fossa CSF space in hemifacial spasm

Abstract

Background: We hypothesize that a smaller posterior fossa (PF) CSF space may be a risk factor for hemifacial spasm (HFS).

Objective: We conducted a case-control 3-dimensional magnetic resonance (MR) volumetric study in patients with HFS and determined the clinical predictive factors of PF CSF volume.

Methods: Patients with clinically diagnosed HFS and controls matched for age, sex, race, and hypertension underwent MRI/magnetic resonance angiography examination. The PF CSF space was segmented and quantified on a heavily T2-weighted high-resolution 3-dimensional MR volume slab, centered over the porus acusticus.

Results: Eighty-two study subjects (41 patients and 41 controls) were included. The mean PF CSF volume in patients with HFS and controls was 17,303.0 +/- 3,900.0 vs 19,216.0 +/- 3,912.0 mm(3). The mean volume in patients with HFS was 11.4% smaller than in controls (p = 0.015). Analysis of differences between individually matched pairs and controls also revealed that PF CSF for controls was larger than that for patients with HFS (p = 0.007). A multivariate linear regression analysis revealed that a small PF CSF volume was associated with HFS (p = 0.01). Decreasing age (p = 0.001) and female gender (p < 0.0005), but not hypertension (p = 0.892), were also found to be predictors of a low PF CSF volume.

Conclusions: Our results showed that the posterior fossa (PF) CSF volume was lower in patients with HFS compared with matched controls. HFS, female gender, and younger age were associated with smaller PF CSF volume. These observations could explain the strong female preponderance in both clinic- and population-based epidemiologic studies.

Figure 1 Segmentation of posterior fossa CSF space The segmented posterior fossa CSF space is represented by the hyperintense space between the outer red line, defining the dural contours, and the inner red line, defining the brain outline. This is demonstrated on representative axial constructive interference at steady state magnetic resonance images from the superior-most (A), mid (B), and inferior-most (C) sections from the 2-cm volume slab centered over the porus acusticus, depicted as a box over the midsagittal image of the brainstem in D.

Figure 2 Posterior fossa CSF volume in a patient with HFS and a control Comparison of 3-dimensional volume rendered constructive interference at steady state images of segmented posterior fossa CSF in a 58-year-old male control subject (left) and a 56-year-old female patient with hemifacial spasm (HFS) (right) when viewed (A) posteriorly, superiorly, and left and (B) below and right of the midline. The control subject has a large posterior fossa CSF volume of 30,070 mm³ compared with a small volume of 10,947 mm³ in the patient with HFS.

Figure 3 Scatterplot of CSF volumes in patients with HFS and controls Scatterplot showing the differences in posterior fossa CSF volume (mm³) between matched pairs of patients with hemifacial spasm (HFS) and controls.