Not much has been known about the glymphatic pathway until recently. The glymphatic pathway is the brain’s version of the lymphatic system found in the rest of the body, though the anatomical structure of the glymphatic pathway is different from the lymphatic system. Scientists believe the pathway is a homeostatic feature that helps the brain maintain a stable extracellular environment by allowing clearance of waste materials from the brain.
Within the glymphatic pathway, cerebrospinal fluid (CSF) filters through the brain and is exchanged with interstitial fluid (ISF) to clear waste. The lymphatic system does something similar to clear waste from other organs. The glymphatic pathway operates most efficiently during sleep, clearing away “brain waste” like amyloid and tau proteins, two substances that can harm brain processes if they accumulate too much.
Medical Imaging of the Glymphatic Pathway
The glymphatic pathway is believed to be made up of three components, which are linked in series:
• The para-arterial CSF influx route
• The transparenchymal pathway
• The para-venous CSF interstitial fluid clearance route
This system can be imaged by using dynamic contrast-enhanced magnetic resonance imaging (MRI). With this type of imaging, MRI scans are taken dynamically after a contrast agent is injected. It’s used for diagnostic radiology procedures like analyzing the blood vessels generated by a brain tumor. With dynamic MRI, concentration of the contrast agent is measured as it passes from blood vessels to extracellular space of the tissues and as it goes back to blood vessels.
New Glymphatic Pathway Data
Scientific evidence is emerging showing the glymphatic system is important in cleaning waste products from the brain. When these products aren’t cleaned out, they can accumulate in the extracellular space. Glymphatic flow increases during sleep, and researchers now believe that glymphatic system dysfunction may be a factor in development of diseases like Alzheimer’s and in recovery from traumatic brain injury and stroke.
Alzheimer’s disease is characterized by decreased clearance of soluble amyloid beta, and traumatic brain injury also appears to affect clearance of waste products. In cases of repeated, low-energy impacts (like those often experienced by football players and boxers), in the weeks following an injury, bulk transport of fluid from the interstitial space to the para-venous CSF pathway is believed to be impaired, resulting in impaired clearance of products like amyloid beta. This information could potentially be extremely important to radiologists like Carl Raboi, MD, who routinely use diagnostic imaging of the brain and nervous system.
A Medical Imaging Study in Rats
Researchers at Stony Brook University School of Medicine used dynamic contrast MRI to study the glymphatic pathway in rodents, identifying and defining these pathways during sleep. They recently published a paper in The Journal of Neuroscience titled “The Effect of Body Posture on Brain Glymphatic Transport” examining CSF-ISF exchange in the brains of anesthetized rodents in three sleeping positions: lateral, prone, and supine.
Glymphatic transport was most efficient in the lateral position. In the prone (on belly) position, transport was slowed, the tracer was cleared more slowly, and there was outflow of CSF along some of the vessels. Glymphatic transport in supine (on back) position was better than prone, but lateral positions were the best as far as efficient glymphatic transport.
What Might This Mean for Diagnostic Radiology?
The researchers propose that body posture and sleep quality should be taken into account when using diagnostic imaging to assess CSF-ISF transport in humans. Assessment of clearance of damaging brain proteins that can contribute to brain diseases may become more important to radiologists like Robert Baker, MD, who specialize in neuroradiology and interventional radiology. The Stony Brook researchers have not done similar studies on humans, but recommend that such studies be conducted for further clarification.
Sleep Studies and the Future of Medical Imaging
Sleep, it appears, serves an important biological function, that of cleaning up the waste products that accumulate while we’re awake. Furthermore, sleeping position appears to affect how well the brain clears out these waste products. Further elucidation of this process may help doctors better assess patients with devastating diseases like Alzheimer’s and those who experience traumatic brain injury. To learn more about how your practice, hospital, or imaging center can benefit from the expertise of the Board-certified radiologists of SteleRAD, we encourage you to call us at 954-358-5250, or contact us online at any time.