​​Focus: This paper is a review article focusing on the significant role of meningeal lymphatic drainage in central nervous system (CNS) diseases.

Method: This paper is a review article.

Finding: Meningeal lymphatic vessels play a crucial role in draining CSF, metabolic byproducts (such as amyloid-β proteins), and immune cells from the CNS, and their dysfunction is increasingly recognized as a significant factor in the pathogenesis and progression of various CNS diseases, including neurodegenerative disorders, stroke, and traumatic brain injury.

Limitation: Understanding of regulatory and damage mechanisms of meningeal lymphatics under physiological and pathological conditions is currently limited.

​​Focus: New evidence regarding CSF transport mechanisms at the brain–meningeal border, including glymphatic and meningeal lymphatic systems, and their implications for neurological health and diseases.

Method: Review article synthesizing current knowledge on CSF transport.

Finding: “The existence of specialized structures that allow a continuous exchange of CSF between different anatomical compartments at the brain–meningeal border is challenging conventional notions around molecular transport within the brain.“

Limitation: The precise mechanisms of CSF-to-dura mater transport and immune cell trafficking remain poorly understood, particularly in humans.

​​Focus: Provide proof-of-principle evidence that the perivascular space in humans functions as a conduit for CSF flow into the brain parenchyma.

Method: Contrast agent administers intrathecally in 5 neurosurgical patients. Two postcontrast brain MRIs performed at 12, 24, or 48 hours.

Finding: CSF flows through perivascular spaces into the brain parenchyma, confirming the existence of a glymphatic pathway in humans.

Limitation: Small sample size.

​​Focus: CNS lymphatic drainage to cervical lymph nodes in humans in-vivo.

Method: MRI following intrathecal contrast agent administration.

Finding: “The time course of lymph node enhancement coincided with brain glymphatic enhancement rather than with CSF enhancement.”

Limitation: Measurement errors may arise from image noise and partial averaging effects, despite efforts to minimize them.

​​Focus: Investigating whether sleep-active glymphatic function contributes to the overnight clearance of amyloid beta (Aβ) and tau from the human brain.

Method: A clinical randomized crossover study where participants underwent both overnight normal sleep and overnight sleep deprivation conditions. Plasma AD biomarkers measured at evening and morning timepoints.

Finding: Sleep-active glymphatic function significantly enhances the overnight clearance of Aβ and tau from the human brain into plasma in healthy individuals.

Limitation: The study included a large number of regressors given the relatively small number of amyloid-positive participants.

Dr. John Kipnis

Reveals how meningeal lymphatics, cerebrospinal fluid (CSF) dynamics, immune signaling, and sleep-dependent clearance mechanisms are integral to brain health, aging, and neurodegenerative diseases.

​​Focus: This study focuses on cerebrospinal fluid (CSF)-mediated brain clearance, particularly insights gained from human studies. It investigates the essential role of brain fluids, primarily CSF and interstitial fluid exchange, in removing waste products from brain metabolism and by-products of brain injury.

Method: Intrathecal Contrast-Enhanced Magnetic Resonance Imaging (gMRI), Phase-Contrast MRI, CSF Clearance Test (Blood-based).

Finding: CSF is essential for brain clearance, exchanging with interstitial fluid to remove waste products. Impaired clearance leads to the accumulation and aggregation of proteins, a hallmark of neurodegenerative and dementia diseases.

Limitation: A key question remains unanswered: to what extent does CSF-mediated brain clearance contribute to overall brain solute clearance compared to local proteolytic degradation and active transport over the blood-brain barrier in various brain regions.

​​Focus: The study’s primary focus is to investigate the extent to which the subarachnoid cerebrospinal fluid (CSF) compartment directly communicates with the extravascular compartment of human brain tissue.

Method: This study was a prospective and observational investigation that examined the distribution and clearance of a CSF tracer in the human brain using MRI.

Finding: The study provides in vivo evidence, for the first time, of brain-wide CSF tracer enhancement and clearance in humans at a rate suggesting a significant role for bulk flow and vascular pulsations rather than pure diffusion. It also showed a delayed tracer clearance in patients with dementia.

Limitation: Assessment of cerebral clearance with MRI by absolute quantities is not possible at the current level, as the normalized T1 signal cannot be assumed to be strictly proportional to the amount of contrast agent in each image voxel.

​​Focus: The study’s focus is to determine the effect of acute sleep loss on Alzheimer’s disease (AD) biomarkers in plasma, specifically amyloid beta (Aβ) and tau.

Method: This study utilized a cross-over design involving five cognitively normal, amyloid-negative participants. Each participant underwent both a sleep-deprived condition and a normal sleep control condition, separated by 4-6 months. During both conditions, cerebrospinal fluid (CSF) and blood samples were collected every 2 hours over a 36-hour period using venous and lumbar catheters.

Finding: A key finding of the study is that one night of sleep deprivation has opposing effects on AD biomarkers in CSF and plasma. This suggests that sleep loss decreases the clearance of these biomarkers from the central nervous system and disrupts their transport between CSF and blood.

Limitation: A small number of participants. All five participants were cognitively normal and amyloid-negative, which prevents the extension of these results to individuals with amyloid deposition, cognitive impairment, or medical comorbidities that might affect brain clearance or alter plasma AD biomarkers.