MRI of CSF flow in normal pressure hydrocephalus

MR imaging is the premier imaging modality for diagnosing the various forms and causes of hydrocephalus. Although CT is satisfactory for imaging in the axial plane, MR imaging is capable of imaging in any plane to better demonstrate any cause of observation. MR imaging also is more sensitive than CT to interstitial edema (transependymal flow of cerebrospinal fluid [CSF]) and to the hyperdynamic CSF flow seen with shunt-responsive normal-pressure hydrocephalus (NPH). MR imaging also is sensitive to the presence of deep white matter ischemia that may contribute to the cause of the idiopathic form of NPH.

Superficial siderosis is associated with chronic blood loss into the cerebrospinal fluid. The pattern of hemosiderin deposition and clinical signs in superficial siderosis suggest that cerebrospinal fluid is recirculated into the ventricular system. Patterns of deposition of corpora amylacea and findings in normopressure communicating hydrocephalus also support the recirculation theory. ‘Free’ iron with excess production of hydroxyl radicals is the probable mechanism of tissue damage. The arachnoid villus-superior saggital sinus theory of cerebrospinal fluid circulation should be abandoned.

Evidence is presented to support the hypothesis that cerebrospinal fluid (CSF) is transported through the tela choroidae and recirculated in the ventricular system. The concept that the CSF is resorbed by the arachnoid villus-superior sagittal sinus system is accepted as fact. The experimental studies on which the currently accepted theory is based were published in 1914 by Dr Lewis Weed. Weed used a low pressure (near physiologic) method and a high pressure (non-physiologic) method. His observations with the high pressure method are a basis for the theory of arachnoid villus absorption. On the other hand, his low pressure method provides evidence that CSF is absorbed in the area of the basilar cisternae. Studies of communicating hydrocephalus and chemical analysis of ventricular melatonin give evidence that CSF recirculates through the tela choroidae back into the ventricles.