Leptomeningitis and Perivascular Spread

Many blood vessels that supply the brain and spinal cord initially run within the covering layers on the external surface, called the leptomeninges (also known as the pia-arachnoid), before plunging into the deeper neural tissue. As the vessel transitions from the outer layers into deeper tissue, the perivascular space immediately surrounding the vessel, called Virchow-Robin space, may provide a conduit for infectious/inflammatory processes.  The inflammatory cells in this image of the spinal cord, which are concentrated in the pia-arachnoid (thereby indicating the presence of leptomeningitis), are easily able to traverse into the inner regions of the spinal cord by following along the blood vessels in the perivascular spaces.