Advanced Neuroimaging in Idiopathic Intracranial Hypertension (IIH)

Abstract

Abstract: : Purpose: Idiopathic intracranial hypertension (IIH) is a disorder associated with intracranial pressure greater than 250 mm water, normal neuroimaging and normal cerebral spinal fluid content. Earlier studies of IIH (Lorberboym et al. 2001) have shown reduced cerebral perfusion using SPECT. The aim of this study was to investigate the effect of increased intracranial pressure on brain perfusion and white matter integrity using MRI. Methods: 3 patients with IIH were studied. All patients underwent CT and MRI scanning which were normal. The CSF pressure of all patients was above 250 mmH2O. MRI was performed on a 1.5T GE Signa MRI scanner. The MRI protocol included T­1, T2 and FLAIR images and MR Angiography. Perfusion weighted images (relative cerebral blood volume (rCBV), relative cerebral blood flow (rCBF) and mean transient time (MTT)) were acquired using a bolus injection of GdDTPA (0.5mmole/kg). In addition low b value DTI (b­max=1000 s/mm2, δ_upper;/δ=31/25ms) and high b value DWI (bmax=14,000 s/mm2, δ_upper;/δ=72/65ms) were also acquired. The q-Space displacement and probability images were computed from the high b value data set. Results: Q-space analysis demonstrated a 47% increase in diffusion displacement in the right temporal-occipital lobes compared to the contralateral side. Perfusion analysis of the affected area, demonstrated marked reduction of both blood flow and blood volume with rCBF and rCBV 30% and 27% of contralateral side respectively (see image 1). In contrast the MTT was only mildly reduced (89%). Conclusion: To date, the radiological diagnosis of IIH is one of exclusion, with no reproducible positive features described in the imaging literature. It is currently believed that there is no resultant damage to the brain in these patients. Management is focused on headache relief and retaining adequate optic nerve function. Our results in this preliminary study indicate marked hypoperfusion and in areas of subcortical white matter in IIH patients.  

Keywords: imaging/image analysis: clinical • neuro-ophthalmology: cortical function/rehabil • neuro-ophthalmology: diagnosis