Dynamic properties of lymphatic pathways for the absorption of cerebrospinal fluid

To study the dynamics of the outflow of cerebrospinal fluid (CSF) into the cervical lymphatic system, X-ray contrast medium or Indian ink was infused into the cisterna magna of rats at moderately increased intracranial pressure (40-50 mmHg). In the first series of experiments, while the contrast medium was being infused, the animal's head was examined using X-ray-microscopy (x4-20 direct magnification radiography) and conventional radiography. Within the first minutes of infusion, the flow of CSF was directed from the posterior fossa to the olfactory bulb. Reaching the cribriform plate approximately 7 min after starting the infusion, the contrast medium leaked into the nasal cavities. Some minutes later, it opacified the subarachnoid space (SAS) of the optic nerve, the perilymphatic space of the inner ear, the cortical SAS, and the transverse sinuses. Leakage from the optic nerve SAS into the orbit was seen after 30 min infusion. In the second series of experiments, the Indian ink was infused after microsurgical exposure of the cervical lymph vessels. During the infusion the cervical lymph ducts were observed microscopically (x40 magnification). Single dye particles draining through the cervical lymph ducts appeared 20 min after the start of cisternal infusion. Their transport was rapid, and dependent on the respiratory cycle: during inspiration the particles moved at a speed of 10-20 mm/s, during expiration the movement stopped. Thus, rapid kinetics are demonstrated for the outflow of CSF and particles from the SAS into the cervical lymphatics.