Neuroimaging in the diagnosis of idiopathic intracranial hypertension.

Traditionally, the primary role of imaging in the diagnosis of idiopathic intracranial hypertension (IIH) has been to exclude other conditions that can cause increased intracranial pressure (ICP) and papilledema. Over the years multiple attempts have been made to define objective signs on cross-sectional imaging as well as on cerebral angiography that would actually identify IIH patients rather than only exclude other underlying conditions. There was also hope that mechanism-derived' imaging techniques such as magnetic resonance venography (MRV) and diffusion weighted imaging would potentially provide insight into the still unknown underlying etiology of this disease. It was recently shown in a double blind controlled study that flattening of the posterior aspect of the globe is the only sign on cross-sectional imaging that, if present, strongly suggests the diagnosis of IIH. In addition, evaluation of extra-luminal and intra-luminal narrowing of the transverse and sigmoid dural sinuses with contrast enhanced MRV using a simple grading system provides a highly sensitive and specific test for identifying patients with IIH. Unfortunately none of the imaging based studies published to date can explain the pathogenesis of IIH whether it be a primary vascular venous disorder causing the increase in ICP or rather the disorder itself secondarily affecting the cerebral veins.