DRAINAGE OF CSF THROUGH LYMPHATIC PATHWAYS AND ARACHNOID VILLI IN SHEEP - MEASUREMENT OF I-125 ALBUMIN CLEARANCE

We investigated lymphatic drainage pathways of the central nervous sys tem in conscious sheep and quantified the clearance of a cerebrospinal fluid (CSF) tracer into lymph and blood. In the first group of studie s, I-125-HSA was injected into the lateral ventricles of the brain or into lumbar CSF and after 6 h, various lymph nodes and tissues were ex cised and counted for radioactivity. Multiple lymphatic drainage pathw ays of cranial CSF existed in the head and neck region defined by elev ated I-125-HSA in the retropharyngeal/cervical, thymic, pre-auricular and submandibular nodes. Implicated in spinal CSF drainage were mainly the lumbar and intercostal nodes. In a second group of experiments, m ultiple cervical vessels and the thoracic duct were cannulated and lym ph diverted from the animals. Transport of tracer through arachnoid vi lli was taken from recoveries in venous blood. Following intraventricu lar administration, the 6 h recoveries of I-125-HSA in the lymph (sum of cervical and thoracic duct) and blood were 8.2% +/- 3.0 and 12.5% /- 4.5 respectively and at 22 h, 25.1% +/- 6.9 and 20.8% +/- 4.1 respe ctively. When I-125-HSA was injected into lumbar CSF, the 6 h recoveri es of tracer in thoracic duct and blood were 11.6% +/- 2.7 and 16.3% /- 3.7 respectively. Total lymph and blood recoveries were not signifi cantly different in any experiment. We conclude that the clearance of I-125-HSA from the CSF is almost equally distributed between lymphatic and arachnoid villi pathways.