Quantifying response to intracranial pressure normalization in idiopathic intracranial hypertension via dynamic neuroimaging

Background: Idiopathic intracranial hypertension (IIH) is characterized by elevated intracranial pressure without a clear cause.

Purpose: To investigate dynamic imaging findings in IIH and their relation to mechanisms underlying intracranial pressure normalization.

Study type: Prospective.

Population: Eighteen IIH patients and 30 healthy controls.

Field strength/sequence: T₁ -weighted, venography, fluid attenuation inversion recovery, and apparent diffusion coefficients were acquired on 1.5T scanner.

Assessment: The dural sinus was measured before and after lumbar puncture (LP). The degree of sinus occlusion was evaluated, based on 95% confidence intervals of controls. We studied a number of neuroimaging biomarkers associated with IIH (sinus occlusion; optic nerve; distribution of cerebrospinal fluid into the subarachnoid space, sulci and lateral ventricles (LVs); Meckel's caves; arachnoid granulation; pituitary and choroid plexus), before and after LP, using a set of specially developed quantification techniques.

Statistical tests: Relationships among various biomarkers were investigated (Pearson correlation coefficient) and linked to long-term disease outcomes (logistic regression). The t-test and the Wilcoxon rank test were used to compare between controls and before and after LP data.

Results: As a result of LP, the following were found to be in good accordance with the opening pressure: relative compression of cerebrospinal fluid (R = -0.857, P < 0.001) and brain volumes (R = -0.576, P = 0.012), LV expansion (R = 0.772, P < 0.001) and venous volume (R = 0.696, P = 0.001), enlargement of the pituitary (R = 0.640, P = 0.023), and shrinkage of subarachnoid space (R = -0.887, P < 0.001). The only parameter that had an impact on long-term prognosis was cross-sectional size of supplemental drainage veins after LP (sensitivity of 92%, specificity of 20%, and area under the curve of 0.845, P < 0.001).

Data conclusion: We present an approach for quantitative characterization of the intracranial venous system and its implementation as a diagnostic assistance tool. We conclude that formation of supplementary drainage veins might serve as a long-lasting compensatory mechanism.

Level of evidence: 2 Technical Efficacy: Stage 3 J. Magn. Reson. Imaging 2018;47:913-927.