Table 2 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.