Alternative pathways for drainage of cerebrospinal fluid in the canine brain.

Although the brain has no formal lymphatic system, a substantial quantity of cerebrospinal fluid (CSF) has nonetheless been shown to drain via cervical lymphatics. To pursue further the issue of alternative drainage pathways for CSF, we infused a solution of Ringer's lactate (RL) into the cisterna magna of the dog brain and monitored both the flow and concentration of total protein of cervical lymph. This maneuver promoted a nearly three-fold rise in intracranial pressure and was accompanied by a rise in cervical lymph flow and fall in its protein content. In addition, a profuse nasal discharge (11.4 ml/hr) developed with a moderately high protein content of the rhinorrhea fluid (1.8 g/dl), along with similar appearance times of Evans blue dye (instilled in the cisterna magna) in both cervical lymph and the rhinorrhea fluid (48-70 minutes after infusion). These findings suggest alternative drainage pathways for CSF besides the arachnoid villi (Pacchionian bodies) including connections with lymphatics in the neck and along the olfactory nerve, and around the cribiform plate to the nasal submucosa, and with proptosis, perhaps also through the aqueous humor-canal of Schlemm and nasolacrimal duct.