CSF enters the brain along para-arterial channels for exchange with interstitial fluid (ISF), which is in turn cleared from the brain along paravenous pathways for ultimate clearance via cervical lymphatic vessels [17, 19].
Such a paravascular "retino-orbital" continuity has previouslybeen suggested  and would include a para-arterial CSF influx route around the central retinal artery to enter the paravascular spaces of the retina, followed by a paravenous clearance efflux route around the central retinal vein (Figures 1(a) and 1(b)) .
approach for the saphenous nerve block.
Bilateral macular coloboma and pigmented paravenous
Studies [7, 8] indicate the existence of a brain-wide pathway facilitating the exchange of CSF and interstitial fluid via para-arterial CSF influx, paravenous
interstitial clearance, and a transparenchymal pathway dependent on water transport through astrocytic AQP4 channels.
Because the initial manifestations can be subtle, extravasation must be differentiated from other paravenous
reactions, such as flare or recall reactions.