Chronic communicating hydrocephalus and periventricular white matter disease: a debate with regard to cause and effect.

For an increasing number of pathologic conditions, the in vivo information obtained by radiologic brain imaging is often more accurate than that obtained from postmortem examination of the brain. This is true for the intriguing and complex condition of "normal pressure" hydrocephalus (NPH). Patients with NPH often are helped dramatically by shunting, which can mean the difference between being in a wheelchair (or bedridden) and being ambulatory, with additional improvement, though usually less dramatic, in cognitive function and memory. Though clinicians are turning increasingly to the neuroradiologist to determine whether hydrocephalus is present, a set of definitive and consistent in vivo diagnostic markers remains elusive. It is for these reasons that innovative work in this field is of great interest to radiologists as well as to clinicians. However, to convince the clinical community of the usefulness of our findings , we must apply the same stringent criteria used in other scientific disciplines. In this issue of the AJNR, Bradley et al. [1] attempt to establish a cause-and-effect relationship between white matter lesions and hydrocephalus. I would like to discuss three issues related to their article: the pathology of periventricufar I white matter lesions, the relationship of white matter disease to hydrocephalus, and the diagnosis of NPH.