Intracranial Hypotension: Improved MRI Detection With Diagnostic Intracranial Angles

OBJECTIVE. Intracranial hypotension is an uncommon cause of headaches that is often misdiagnosed. The classic MRI features of intracranial hypotension can be variable and subjective. The purpose of this study was to provide objective criteria in the MRI evaluation of intracranial hypotension by quantifying normal values for the pontomesencephalic angle, mamillopontine distance, and lateral ventricular angle. MATERIALS AND METHODS. A retrospective review of patients with the clinical diagnosis of intracranial hypotension and a control group was performed with measurements of the pontomesencephalic angle, mamillopontine distance, and lateral ventricular angle. Qualitative evaluation of other MRI findings included dural enhancement, venous engorgement, subdural collections, brainstem slumping, and tonsillar herniation. RESULTS. In 29 patients with intracranial hypotension, the mean pontomesencephalic angle, mamillopontine distance, and lateral ventricular angle were 41.2 degrees (SD, +/- 17.4 degrees), 4.4 mm (SD, +/- 1.8), and 130.1 degrees (SD, +/- 9.8 degrees), respectively. In the control group, the mean pontomesencephalic angle, mamillopontine distance, and lateral ventricular angle were 65 degrees (SD, +/- 9.9 degrees), 7.0 mm (SD, +/- 1.3), and 132.2 degrees (SD, +/- 5.7 degrees), respectively. The differences in the pontomesencephalic angle and mamillopontine distance values for the intracranial hypotension group versus the control group were statistically significant (p < 0.01). The difference in the lateral ventricular angle measurements was not statistically significant (p = 0.37). Cutoff points of a 5.5-mm mamillopontine distance and 50 degrees pontomesencephalic angle were estimated using receiver operating characteristic curves. CONCLUSION. In patients with the clinical suspicion of intracranial hypotension, we found that cutoff values of 5.5 mm or less for the mamillopontine distance and 50 degrees or less for the pontomesencephalic angle were sensitive and specific in strengthening the qualitative MRI findings. Therefore, quantitative assessments may provide a more accurate diagnosis.