Non-invasive assessment of intracranial compliance in idiopathic intracranial hypertension: an MRI-ICP study

Idiopathic intracranial hypertension (IIH) is a disease which threatens vision and causes disabling headaches, affecting women of childbearing age with obesity. It is characterised by raised intracranial pressure (ICP), measured invasively either with lumbar punctures or intracranially-inserted monitors. There is an unmet clinical need to develop non-invasive means to assess ICP. This study aims to utilise the MRI-ICP imaging technique to measure intracranial compliance index and assess its suitability as surrogate biomarker of ICP.

Nine IIH patients and ten age, sex, and body mass index matched healthy controls were recruited. All participants underwent lumbar puncture, visual assessments, detailed headache phenotyping, and MRI-ICP scans to calculate intracranial compliance index at baseline. Following treatment, patients were invited to attend a one-year visit when all assessments were repeated.

There was significant (p = 0.017) reduction in intracranial compliance index in IIH (mean = 1006.0 cc/mmHg/cm, SD = ± 384.6 cc/mmHg/cm) compared to controls (mean = 1493.0 cc/mmHg/cm, SD = ± 411.8 cc/mmHg/cm), inversely correlating with lumbar puncture opening pressure (r = -0.502, p = 0.029). A significant inverse correlation between compliance index and headache disability was also found (r = -0.458, p = 0.049) and a trend for an association between lower compliance index and increased frequency of headaches (r = -0.430, p = 0.066). This latter became significant (p = 0.018) after accounting for use of analgesics. Following successful treatment, compliance index was increased in all patients at one year (mean of differences = 380.7 cc/mmHg/cm, p = 0.031).

This is the first study to apply the MRI-ICP technique longitudinally in IIH. It illustrates reduced intracranial compliance index in IIH, correlating with opening pressure and headache disability and ameliorating with treatment.