A new model of the cerebrospinal fluid (CSF) circulation, involving brain capillaries as the main site of CSF absorption, is proposed from the Karolinska MR Research Center and Department of Neuroradiology, Karolinska Hospital, Stockholm, Sweden. In communicating hydrocephalus, a decrease of CSF flow through the foramen magnum demonstrated by MRI is explained by restricted expansion of the intracranial arteries. In the new classification, communicating hydrocephalus is called “restricted arterial pulsation (RAP) hydrocephalus,” a primary hemodynamic disturbance, caused by any process that decreases compliance of arteries, eg ectasia, arteritis, spasm. In obstructive hydrocephalus, ventricular dilatation causes compression of cortical veins, a secondary hemodynamic disturbance called “venous congestion (VC) hydrocephalus.” Pharmacological treatment for hydrocephalus should consist of selective venous constrictor drugs such as dihydroergotamine. 
COMMENT. The authors caution that treatment of hydrocephalus with dihydroergotamine should not be employed in children until more studies are completed in adults. The new hemodynamic mechanism for hydrocephalus is more in keeping with studies involving flow sensitive MR imaging and radionuclide cisternography. As noted by Whitelaw A, in an editorial commentary, one of the strongest arguments against the conventional model of CSF circulation and absorption is the absence of Pacchionian granulations in children less than 12 months of age. However, the new hemodynamic concept is only a hypothesis which needs to be proven by further studies.