The pathophysiology of the aqueduct stroke volume in normal pressure hydrocephalus: can co-morbidity with other forms of dementia be excluded?

Abstract

Variable results are obtained from the treatment of normal pressure hydrocephalus (NPH) by shunt insertion. There is a high correlation between NPH and the pathology of Alzheimer's disease (AD) on brain biopsy. There is an overlap between AD and vascular dementia (VaD), suggesting that a correlation exists between NPH and other forms of dementia. This study seeks to (1) understand the physiological factors behind, and (2) define the ability of, the aqueduct stroke volume to exclude dementia co-morbidity. Twenty-four patients from a dementia clinic were classified as having either early AD or VaD on the basis of clinical features, Hachinski score and neuropsychological testing. They were compared with 16 subjects with classical clinical findings of NPH and 12 aged-matched non-cognitively impaired subjects. MRI flow quantification was used to measure aqueduct stroke volume and arterial pulse volume. An arterio-cerebral compliance ratio was calculated from the two volumes in each patient. The aqueduct stroke volume was elevated in all three forms of dementia, with no significant difference noted between the groups. The arterial pulse volume was elevated by 24% in VaD and reduced by 35% in NPH, compared to normal (P = 0.05 and P = 0.002, respectively), and was normal in AD. There was a spectrum of relative compliance with normal compliance in VaD and reduced compliance in AD and NPH. The aqueduct stroke volume depends on the arterial pulse volume and the relative compliance between the arterial tree and brain. The aqueduct stroke volume cannot exclude significant co-morbidity in NPH.

The Pathophysiology of Idiopathic Normal Pressure Hydrocephalus: Cerebral Ischemia or Altered Venous Hemodynamics?

“…The hydrodynamics of NPH have been shown to involve a reduction in the compliance of the subarachnoid space, brain, and the arterial tree. 18 The reduced compliance directs a larger proportion of what would otherwise be a reduced total arterial pulsation toward the ventricles, increasing the aqueduct stroke volume. 18 With this in mind, I compared blood flow and compliance measures in a cohort of patients with NPH, selected to have arterial inflows above the normal range, to see if deep brain ischemia or superficial venous hemodynamic changes contribute to the pathophysiology of NPH in these patients.…”

Normal pressure hydrocephalus versus atrophic dilatation to distinguish and predict the benefits of surgical intervention with a phase-contrast MRI technique

“…On the other hand, among older volunteers, no significant difference has been shown between other cognitive disorders and CSF flow rate, and thus the prediction of the potential benefit from surgery. Some consider flow velocity and rate measurements adequate for a differential diagnosis and the prediction of the benefit from surgery, but others think the opposite (4,11,14,17).…”

Current and Emerging MR Imaging Techniques for the Diagnosis and Management of CSF Flow Disorders: A Review of Phase-Contrast and Time–Spatial Labeling Inversion Pulse

“…19 ) Studies of CSF flow in hydrocephalus secondary to intracranial pressure changes demonstrated by invasive monitoring have found up to a 10-fold increased pulsatile aqueductal flow 15,17,[19][20][21][22][23][24] compared with that in healthy controls. This finding has been used to build criteria for diagnosing idiopathic normal pressure hydrocephalus (NPH) based on stroke volumes of Ͼ42 L 19 or pulsatile flow rates above a threshold of 18 mL/min, for example.…”