Table 3 Anomalies at catheter venography of the main extracranial cerebrospinal veins that interfere with normal blood outflow of brain parenchyma described in patients with MS ^a

(1)

 Stenosis: any venous lumen reduction >50% or presence of a trans-stenosis gradient, that is, higher pressure in the IJVs and/or azygos vein compared to pressure in the superior vena cava or the brachiocephalic trunk

(2)

 Septum/valve malformation

(3)

 Inversion of valve direction, twisting of a venous segment with consequent stenosis, hypoplasia of a venous segment or agenesis of a venous segment. In all these cases, angioplasty is not always effective or cannot be done, but it will be reported to differentiate complete from incomplete procedures.

(4)

 Anomalous presence of inverted flow with respect to the physiological direction (for example, in supine position, azygos vein that empties into the left renal vein instead of into the superior vena cava; azygos vein that refluxes into the perivertebral plexus with stasis)

(5)

 External compression, for example, aortic arch compressing the left brachiocephalic trunk with stasis and/or reflux into the IJVs or the vertebral veins; Cockett syndrome and hyperinflows into the lumbar hemiazygos circulation. Such compressions cannot always be treated with angioplasty, but they will be reported to differentiate complete from incomplete procedures.

(6)

 Dysmorphic valve apparatus in presence of fixed membrane in the M-mode test and/or absent flow and/or accelerated flow ≥90 cm/s and/or reflux-bidirectional flow ≥1.5 seconds