Cerebral venous drainage in humans is thought to be ensured mainly via the internal jugular veins (IJVs). However, anatomic, angiographic, and ultrasound studies suggest that the vertebral venous system serves as an important alternative drainage route. We assessed venous blood volume flow in vertebral veins (VVs) and IJVs of 12 healthy volunteers using duplex ultrasound. Measurements were performed at rest and during a transient bilateral IJV and a circular neck compression. Total venous blood volume flow at rest was 766 ± 226 ml/min (IJVs: 720 ± 232, VVs: 47 ± 33 ml/min). During bilateral IJV compression, VV flow increased to 128 ± 64 ml/min. Circular neck compression, causing an additional deep cervical vein obstruction, led to a further rise in VV volume flow (186 ± 70 ml/min). As the observed flow increase did not compensate for IJV flow cessation, other parts of the vertebral venous system, like the intraspinal epidural veins and the deep cervical veins, have to be considered as additional alternative drainage pathways.
Quantifying cerebral hypoxia by near-infrared spectroscopy tissue oximetry: the role of arterial-to-venous blood volume ratio