Outflow of cerebrospinal fluid is predominantly through lymphatic vessels. Reduced in aged mice.

"Dynamic imaging suggested that lymphatic outflow was the major outflow route for CSF [Cerebrospinal Fluid] rather than venous routes, with even small molecular tracers not demonstrating immediate blood uptake. Finally, we have demonstrated a significant decline in CSF outflow in aged mice, a finding that may have significance for many aging-associated neurological disorders."

Source: Nature Communications