Multi-signal Analysis of the Composition and Movement of Fluid in Various Cerebral Compartments in Healthy Subjects and Subjects With White Matter Pathology

Among the various indirect markers of altered drainage of neuroglial waste metabolites, there is the widening of the perivascular spaces (PVS) and the presence of white matter signal alterations.

An increase in the number of PVS and their enlargement could represent an indirect marker of obstruction to the drainage of fluids and solutes along the arterial wall at the level of the white matter. This obstruction would also be the basis of tissue hypoxia resulting in the formation of areas of signal hyperintensity in the white matter (White Matter Hyperintensities, WMH) often observed in patients with neurodegenerative diseases and small vessel disease.

It is currently unclear what the main drainage route of brain waste metabolites is. Surely there are at least two.

The glymphatic theory proposes the entry of the cerebrospinal fluid (CSF) from the subarachnoid space towards the brain parenchyma in a centripetal direction and exit of the metabolic waste along the perivenous spaces. The drainage of metabolic waste could also be explained by the more recent "intramural periarterial drainage" (IPAD) theory which shows elimination along the arterial walls in a centrifugal direction.

In magnetic resonance imaging (MRI), the study of solute drainage requires a dynamic evaluation, which is able to evaluate the temporal movement of a tracer. There are several MRI techniques, already described in the literature, which can be used to obtain information relating to perfusion processes and the coupling of neuronal and vascular activity in different brain areas.