[Emerging concept of the production and absorption of cerebrospinal fluid, and recent progress in the diagnosis and treatment of iNPH].

Recently, there has been emerging a new attractive hypothesis that cerebrospinal fluid (CSF) is not circulating or absorbed from arachnoid villi, but absorbed from capillaries of the brain surface to vasculature or excreting through arterial walls and cribriform plate to cervical lymph nodes. About 90% of patients with iNPH (idiopathic normal pressure hydrocephalus) show DESH (Disproportionately Enlarged Subarachnoid-space Hydrocephalus) sign on brain CT/MRI. Identification of the DESH sign is important for the diagnosis of iNPH, and it is helpful for the judgement whether DESH sign is positive or not to detect apparent hyperperfusion in the high-convexity of the brain in iNPH patients with N-isopropyl-p-[(123)I] iodoamphetamine (IMP) single photon emission computed tomography (SPECT). We have named this characteristic finding in IMP-SPECT as the CAPPAH (Convexity APPArent Hyperperfusion) sign, and would like to emphasize its usefulness in the clinical diagnosis of iNPH.