Changes in Aqueductal CSF Stroke Volume in Shunted Patients with Idiopathic Normal-Pressure Hydrocephalus

Proposed model demonstrating ACSV changes in iNPH. A, In healthy subjects, expansion of the cerebral hemispheres occurs both outwardly and inwardly. The outward expansion produces venous blood outflow as a result of compression on the cortical veins. Inward expansion produces flow of CSF into the aqueduct as a result of compression of the lateral and third ventricles. B, In communicating hydrocephalus, the brain has already expanded outward during diastole, compressing the cortical veins. However, during systole, with arterial blood entering, the systolic expansion is directed inwards, resulting in a much greater ACSV in the aqueduct. C, In unshunted patients with iNPH, progressive ischemia and a reduction of arterial inflow results in a decreased “ventricular CSF pump” and then in a subsequent decrease of ACSV. D, In shunted patients, the shunt creates an alternative to ventricular CSF outflow, and in the patients with reversible iNPH, the shunt recreates both outward and inward brain expansion and the renormalization of ACSV.