|Classification for the extracranial hemodynamic/functional venous abnormalities|
|Venous reflux/bidirectional flow:|
|Valsalva maneuver induced jugular venous reflux:||• Valsalva maneuver-like activities which increase intrathoracic pressure may lead to IJV incompetence, known as jugular vein reflux and measured on DS or IVUS.|
|*Spontaneous venous reflux:||• Present on DS examination in the IJV and vertebral veins and for more than 0.88 seconds with the head at 90° and 0°; delayed emptying time on CV.|
|*Venous reflux in the intracerebral veins:||• Reflux/bidirectional flow on DS in the deep cerebral veins is defined as reverse flow for a duration of 0.5 s in one of the intra-cranial veins.|
|Abnormal venous flow distribution in extracranial veins:||• Measurement of blood flow, blood volume and blood velocity by using DS, MR phase contrast imaging, CV or IVUS.|
|No flow in extracranial veins:||• No flow on DS or IVUS or contrast noted in the vein on CV and MRV, despite deep breaths.|
|Abnormal posture control of IJV flow:||• A negative ∆CSA on DS represents the loss of the normal postural control; altered estimation of changes in venous capacitance and venous resistance by posture change on plethysmography.|
Legend: CSA. cross sectional area; CV, catheter venography; DS, Doppler sonography; IJV, internal jugular vein; IVUS, intravascular ultrasound; MRV, magnetic resonance venography.
*The controversy regarding the methodological validity of these quantitative definitions for spontaneous and intracerebral venous reflux included recent position statements from the ISNVD , the European Society of Neurosonology and Cerebral Hemodynamics (ESNCH)  and review studies  that expressed considerable concerns regarding the accuracy of the proposed criterion.
Zivadinov and Chung
Zivadinov and Chung BMC Medicine 2013 11:260 doi:10.1186/1741-7015-11-260