• Alexander V Shulyakov, Richard J Buist, and Marc R Del Bigio.
• Manitoba Institute of Child Health, Winnipeg, Canada.
• Neurosurgery. 2012 Nov 1;71(5):1032-40.

BackgroundThe mechanisms of hydrocephalus formation remain unclear.ObjectiveTo measure intracranial biomechanical changes in rats with hydrocephalus.MethodsStress-strain relationships were determined by using force-controlled indentation through a craniotomy. Cortical blood flow and intracerebral pressures were monitored. In normal rats, deformability of intracranial contents was examined by applying 100 (20-100 mN) indentation cycles and during a 2-hour stress (100 mN) holding test. Hydrocephalus was induced in 56-day rats by cisternal kaolin injection. Magnetic resonance imaging was used to measure ventricle size and cortical blood flow.ResultsApplication of a constant small force for 2 hours or 100 cycles of a small indentation caused progressive intracranial deformation. Following kaolin injection, the ventricles of 3- to 4-day, 7- to 9-day, and 12- to 15-day hydrocephalic rats progressively enlarged, the dorsal cerebrum thickness decreased by >40%, and cortical blood flow decreased by ∼20%. After 3 to 4 days, intracranial pressure and intraparenchymal pulse pressure increased significantly by ∼85%, and diminished thereafter. After 7 to 9 days, there was a transient significant increase of the intracranial stiffness (indentation modulus). Viscoelastic strain during application of a constant force significantly increased by >50% at 7 to 9 and 12 to 15 days.ConclusionThe observation that very small forces applied exogenously or endogenously (through pulsatile brain micromotions) cause progressive intracranial deformation suggests that the brain behaves in a poroviscoelastic manner. Intracranial pulsatility is increased during the early phases of ventriculomegaly. Small viscoelastic property changes of the intracranial contents accompany the ventriculomegaly. Consolidation of brain tissue by the pulsatile forces likely occurs through displacement of intraparenchymal fluids.

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