Edzard Wiener

Jan Hoffmann

Headaches are one of the most common reasons for patients to seek medical advice. In our headache outpatient department we commonly attend patients suffering from idiopathic intracranial hypertension (IIH), which represents one of the main focus areas of our headache research. Our scientific research activities on IIH have substantially influenced the pathophysiological understanding and the highly specialized medical care of this disabling clinical condition. IIH is a relatively uncommon headache syndrome associated with elevated intracranial pressure (ICP), whose pathophysiological mechanisms are still largely unknown. Current findings indicate that altered cerebrospinal fluid dynamics, including venous outflow resistance, may constitute significant causal factors.

The diagnostic criteria have undergone several modifications and are now defined in the Headache Classification (ICHD-3 beta) of the International Headache Society (IHS). The diagnosis of IIH is based mainly on an elevated CSF opening pressure (> 25 cm H₂O) during lumbar puncture with normal CSF composition; characteristic clinical symptoms, including headache and visual disturbances; and specific MR imaging findings such as an empty sella turcica, distention of the optic nerve sheath (ONS), and flattening of the posterior aspect of the optic globe.

The interpretation of subtle changes on MR images performed for the initial diagnosis or follow-up can be challenging and the radiologic

diagnosis is critically affected by the experience of the neuroradiologist. Only in advanced disease stages do characteristic morphologic signs become clearly visible on MRI, whereas volumetric measurements, in particular if these are automated and observer-independent, could significantly improve diagnostic reliability. Therefore our research currently focuses on evaluating diagnostic strategies that may potentially offer the possibility to diagnose and evaluate treatment efforts without the need for repetitive lumbar punctures.

Our study aimed at evaluating validity and diagnostic reliability of hypophysis, optic nerve sheath, and optic nerve volumes measured on high-resolution MR images in patients with IIH and age-, sex-, and BMI-matched controls. The results show that mean values of ONS (341.86 ± 163.69 mm³ vs. 127.56 ± 53.17 mm³, P < .001) and hypophysis volumes (554.59 ± 142.82 mm³ vs. 686.60 ± 137.84 mm³, P < .05) differed significantly between healthy and diseased subjects, suggesting that volumetric measurements of the ONS and pituitary gland may enhance diagnostic accuracy in IIH. We further investigated a potential correlation between the observed structural abnormalities and the CSF opening pressures during lumbar puncture. Interestingly, we could not identify a significant correlation suggesting that anatomic abnormalities may well be indirect or even comorbid rather than being the direct consequence of elevated ICP. In this context it is still unclear to what extent the brain is compressible and CSF space is affected in response to increasing ICP. However, maybe more sophisticated MR techniques could show alteration in the microstructural connectivity of brain tissue during IIH. In a new study coming soon we will present new results using DTI and a voxelwise cross-subject permutation analysis between patients with IIH and age-, sex-, and BMI-matched healthy volunteers to evaluate the relationship between ICP and microstructural brain tissue abnormalities, helping to improve our understanding of the pathophysiologic concepts for IIH.

Read this article at AJNR.org . . .