Superficial siderosis of the brain: roles for cerebrospinal fluid circulation, iron and the hydroxyl radical.

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.