The pulsating brain: A review of experimental and clinical studies of intracranial pulsatility

The maintenance of adequate blood flow to the brain is critical for normal brain function; cerebral blood flow, its regulation and the effect of alteration in this flow with disease have been studied extensively and are very well understood. This flow is not steady, however; the systolic increase in blood pressure over the cardiac cycle causes regular variations in blood flow into and throughout the brain that are synchronous with the heart beat. Because the brain is contained within the fixed skull, these pulsations in flow and pressure are in turn transferred into brain tissue and all of the fluids contained therein including cerebrospinal fluid. While intracranial pulsatility has not been a primary focus of the clinical community, considerable data have accrued over the last sixty years and new applications are emerging to this day. Investigators have found it a useful marker in certain diseases, particularly in hydrocephalus and traumatic brain injury where large changes in intracranial pressure and in the biomechanical properties of the brain can lead to significant changes in pressure and flow pulsatility. In this work, we review the history of intracranial pulsatility beginning with its discovery and early characterization, consider the specific technologies such as transcranial Doppler and phase contrast MRI used to assess various aspects of brain pulsations, and examine the experimental and clinical studies which have used pulsatility to better understand brain function in health and with disease

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

BACKGROUND/OBJECTIVES: 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.SUBJECTS/METHODS: 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.RESULTS: 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).CONCLUSIONS: 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.</p