Is enhanced-MRI a way for non-invasive evaluation of the glymphatic-meningeal lymphatic system in patients with cerebral small vessel disease? What we currently know

Excerpt

The glymphatic system is a recently discovered waste clearance pathway in the brain [1]. Traditionally, the central nervous system was thought to lack a conventional lymphatic drainage system [2]. However, recent studies have demonstrated that the cerebral spinal flow (CSF) and the interstitial fluid continuously interchange [1, 3]. From the subarachnoid space, CSF is driven into the perivascular spaces, and subsequently into the brain parenchyma, via aquaporin-4 channels in the astrocyte end feet [3, 4]. The CSF exchanges with the interstitial fluid and exits along with waste products toward the perivenous spaces and the meningeal lymphatic vessels of the dura. From these vessels, the CSF drains out of the brain toward the cervical lymph nodes [2, 5]. This drainage has been designated the glymphatic or glymphatic-meningeal lymphatic system (GMLS), because of its similarity to the lymphatic system in the peripheral tissue, and to the role of the glial aquaporin-4 channels. Clearance of brain waste metabolites by the GMLS is enhanced during sleep [6]. On the other hand, impaired drainage is reported in normal aging, sleep disturbances, and in Alzheimer’s and non-Alzheimer dementia [1, 4, 6]. Thus, the knowledge of the GMLS can reveal potential practical implications in neurodegenerative diseases. …