Association between arterial inflow and venous outflow in idiopathic and secondary intracranial hypertension.

Twenty-four patients with a clinical diagnosis of idiopathic intracranial hypertension underwent standard magnetic resonance (MR) imaging. On the basis of MR venography, two groups of patients could be identified: (i) one group with an intrinsic venous outflow obstruction (intrinsic); and (ii) a non-intrinsically obstructed (extrinsic) group. MRI flow quantification studies of the cerebral arteries and veins, measuring arterial blood inflow as well as superior sagittal sinus (SSS) and straight sinus (ST) outflow, were performed. The MR venography confirmed that there were 12 intrinsic patients and 12 extrinsic patients. In the intrinsic group, total arterial inflow was normal; however, the SSS outflow was reduced by 35% (p=0.0001). Arterial inflow in extrinsic patients was 55% higher than normal (p=0.0001); however, the SSS flow was normal. In intrinsic venous outflow obstruction, total cerebral inflow is maintained despite a reduction in outflow. In the idiopathic cases, there was cerebral hyperaemia suggesting a derangement of autoregulation.