Cerebrovascular Reactivity in Idiopathic Intracranial Hypertension Measured by Blood Oxygen Level-Dependent MRI (P04.248)

Abstract

Objective: To characterize cerebrovascular reactivity (CVR) in idiopathic intracranial hypertension (IIH) before and during treatment with acetazolamide. Background IIH is defined by its clinical characteristics: symptoms and signs of raised intracranial pressure (ICP), confirmed by high opening pressure on lumbar puncture with normal cerebrospinal fluid (CSF) content, in the absence of any space-occupying lesion. The pathophysiology remains unknown, though a hypothesized positive feedback loop involving venous hypertension, reversal of the pressure gradient across the arachnoid granulations, and extrinsic compression of venous structures due to high CSF pressure may contribute. It has further been proposed that impaired cerebral autoregulation may be the primary trigger. Measuring the blood oxygen level-dependent (BOLD) MRI response during hypercapnea allows quantification of the cerebral autoregulatory reserve and may be a useful diagnostic test in IIH. Design/Methods: Five patients were studied. Three patients presenting with new onset IIH, confirmed by papilledema, high opening pressure, benign CSF content, and normal MRI/MRV, underwent MRI CVR mapping. In addition, 2 patients with IIH improving on acetazolamide were scanned using the same protocol. CVR maps were individually compared to a group of 29 normal control subjects. Results: In patients with new onset, untreated IIH, CVR was globally reduced throughout the parenchyma, with greatest reductions in the lenticular nuclei bilaterally. Six days following initiation of acetazolamide in one patient, CVR remained globally impaired. After 7 weeks of acetazolamide in a different patient, there was normalization of symptoms and CVR. Conclusions: The MRI measurement of CVR is a promising method to identify patients with IIH and to monitor their response to therapy. Whether the reduction in CVR reflects a primary failure of autoregulation in IIH or is the result of elevated ICP is unclear. Disclosure: Dr. Hui has nothing to disclose. Dr. Sharpe has nothing to disclose. Dr. Poublanc has nothing to disclose. Dr. Chmielewski has nothing to disclose. Dr. Fierstra has nothing to disclose. Dr. Mandell has nothing to disclose. Dr. Mikulus has received personal compensation for activities with the University Health Network. Dr. Mikulus has received royalty payments from RespirAct. Dr. Mikulus holds stock and/or stock options in Thornhill Research Inc.