Ventricular Infusion and Nanoprobes Identify Cerebrospinal Fluid and Glymphatic Circulation in Human Nerves

Cerebrospinal Fluid Flow Extends to Peripheral Nerves

Cerebrospinal fluid (CSF) is an aqueous solution responsible for nutrient delivery and waste removal for the central nervous system (CNS). The three-layer meningeal coverings of the CNS support CSF flow. Peripheral nerves have an analogous three-layer covering consisting of the epineurium, perineurium, and endoneurium. Peripheral axons, located in the inner endoneurium, are bathed in "endoneurial fluid" similar to CSF but of undefined origin. CSF flow in the peripheral nervous system has not been demonstrated. Here we show CSF flow extends beyond the CNS to peripheral nerves in a contiguous flowing system. Utilizing gold nanoparticles, we identified that CSF is continuous with the endoneurial fluid and reveal the endoneurial space as the likely site of CSF flow in the periphery. Nanogold distribution along entire peripheral nerves and within their axoplasm suggests CSF plays a role in nutrient delivery and waste clearance, fundamental aspects of peripheral nerve health and disease.

One Sentence Summary

Cerebrospinal fluid unites the nervous system by extending beyond the central nervous system into peripheral nerves.

Identification of a novel path for cerebrospinal fluid (CSF) drainage of the human brain

How cerebrospinal fluid (CSF) drains from the human brain is of paramount importance to cerebral health and physiology. Obstructed CSF drainage results in increased intra-cranial pressure and a predictable cascade of events including dilated cerebral ventricles and ultimately cell death. The current and accepted model of CSF drainage in humans suggests CSF drains from the subarachnoid space into the sagittal sinus vein. Here we identify a new structure in the sagittal sinus of the human brain by anatomic cadaver dissection. The CSF canalicular system is a series of channels on either side of the sagittal sinus vein that communicate with subarachnoid cerebrospinal fluid via Virchow-Robin spaces. Fluorescent injection confirms that these channels are patent and that flow occurs independent of the venous system. Fluoroscopy identified flow from the sagittal sinus to the cranial base. We verify our previous identification of CSF channels in the neck that travel from the cranial base to the subclavian vein. Together, this information suggests a novel path for CSF drainage of the human brain that may represent the primary route for CSF recirculation. These findings have implications for basic anatomy, surgery, and neuroscience, and highlight the continued importance of gross anatomy to medical research and discovery.