Direct Connections Between the Spinal Epidural Space and the Venous Circulation in Humans

Our previous studies in pigs indicate that direct connections exist between the spinal epidural space and the venous circulation. We wondered if similar connections occur in humans and have extended our investigations to human cadavers awaiting autopsy. We studied 10 recently dead human bodies. We inserted 2 Tuohy needles into the epidural space of the lower thoracic spine at adjacent interspaces. We infused saline with a constant-flow pump into 1 needle and measured the resulting pressure through the other. Epidural pressure increased to a steady plateau during fluid infusion, and this value was recorded at several flow rates. The pressure decay after flow stopped was also recorded. Then we infused radiopaque contrast, removed the needles, and obtained a computed tomographic scan of the spine from the foramen magnum to the coccyx. Pressure in the epidural space increased to a plateau during saline infusion. Higher flow rates produced higher plateau pressures. Plots of plateau pressure versus infusion rate were linear in all bodies. The slope of the flow-pressure plot gave a steady-state resistance (543 ± 638 mm Hg·s/mL). The time constant of the pressure decay curve allowed calculation of initial capacitance (0.090 ± 0.062 mL/mm Hg). Contrast could be identified in veins around the spinal column in all bodies. Contrast was found most commonly in the deep veins of the neck (7 bodies) and in veins originating in the area of the brachial plexus (7 bodies). Contrast was found less commonly and in smaller amounts in veins draining into the azygous system (5 bodies) and the lumbar veins (5 bodies). No contrast was found in veins in the sacral area. A direct connection between the spinal epidural space and the venous circulation has been demonstrated in human cadavers. The connection is most commonly found in the cervical and upper thoracic spine.