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Table 1 Classification of the venous drainage pathways due to the extracranial structural/morphological, venous abnormalities

From: Potential involvement of the extracranial venous system in central nervous system disorders and aging

Types [10, 11, 22, 27, 37, 110, 111, 115, 120] Definition
Intra-luminal: Web: multiple septae and/or flaps located in a cluster.
This is an echogenic structure detected by DS or by IVUS extending from the endothelial lining of the vein wall with/without the presence of functional abnormality. Use of a diluted angiographic contrast may help identification of these abnormalities on CV. These abnormalities include web, flap, septum, membrane, hyperechoic filling defect, double parallel lumen and malformed valve. Flap: thin linear echogenic structure extending from the endothelial lining of a vein wall.
Septum: thin linear echogenic structure extending from the endothelial lining of a vein wall and attached to it at both ends. The septum may extend across a vein to attach on opposing sides or attach on the same side.
Membrane: membranous structure almost occluding the entire diameter of the vein.
Hyperechoic filling defect: an eccentric hyperechoic crescent with a distinct sonographic signal, reminiscent of chronic organized thrombus.
Double parallel lumen: multiple small channels in the venous wall.
Malformed valve: dysdynamic or fibrous valve.
Extra-luminal: Narrowing: presence of significant narrowing (defined as venous lumen reduction ≥50% respect to the proximal adjacent vein segment on CV or CSA measurement of proximal IJV ≤0.3 cm2 on DS.
This is a restriction of the venous wall or narrowing detected on DS, CV, IVUS or MRV. These abnormalities include narrowing and annulus. Annulus: circumferential thickened vein wall that is restricting the vein from fully expanding with respiratory or positional changes.
• Vein wall not reacting to a given change in transmural pressure on CV, IVUS or DS; non-compliant.
Abnormal IJV distensibility/pulsatility/paradox:  
  1. Legend: CSA, cross sectional area; CV, catheter venography; DS, Doppler sonography; IJV, internal jugular vein; IVUS, intravascular ultrasound; MRV, magnetic resonance venography.