The Value of Integrating Fluorescent Imaging and Immunohistochemistry for Future Anatomical Studies in Aesthetic Surgery: Lessons From the Cerebrospinal Fluid Circulatory System of Human Nerves and Brain

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.

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

Growing evidence suggests that cerebrospinal fluid circulates in human nerves. Several conditions encountered by the plastic surgeon may be related to dysregulation of this system, including nerve transection, stretch injuries, and peripheral neuropathy. The purpose of this study was to show how ventricular infusion and nanoprobes identify CSF and glymphatic circulation in neural sheaths of human nerves.

METHODS

The technique of ventricular infusion using buffered saline was developed in 2017. The technique was used in a series of eight fresh cadavers before dissection of the median nerve, and combined with fluorescent imaging and nanoprobe injections in selected specimens.

RESULTS

Eight cadaver specimens underwent ventricular infusion. There were six female and two male specimens, ages 46-97 (mean 76.6). Ventricular cannulation was performed successfully using coordinates 2 cm anterior to coronal suture and 2.5 cm lateral to sagittal suture. Depth of cannulation ranged from 44 to 56 mm (mean 49.7). Ventricular saline infusion complemented by nanoprobe injection suggests CSF flows in neural sheaths, including pia meninges, epineurial channels, perineurium, and myelin sheaths (neurolemma).

CONCLUSIONS

Ventricular infusion and nanoprobes identify CSF flow in neural sheaths of human nerves. CSF flow in nerves is an open circulatory system that occurs via channels, intracellular flow, and cell-to-cell transport associated with glial cells. Neural sheaths, including neurolemma, may participate in glucose and solute transport to axons. These techniques may be used in anatomic dissection and live animal models, and have been extended to the central nervous system to identify direct ventricle-to-pia meninges CSF pathways.