http://www.springerlink.com/content/j23 ... lltext.pdf
Some interesting snippets:
In one case the reflux appeared to be related to the arm position.
A 71-year-old female, was seen for headache, ataxia, and incoordination,
howed on the posterior angiogram a very important venous reflux,
not only jugular but reaching the lateral sinus and even the longitudinal
sinus, to the right lateral sinus and jugular vein.
The cause can be an organic more or less complete
obstruction of an innominate vein, as in some malignant
anterior mediastinal tumors, or in mediastinal
goiter  or aortic aneurysm .
The reflux was ascribed
to variations of blood flow in veins with absent or
incompetent valves, accentuated in some instances by
a Valsalva maneuver.
As a matter of fact, this kind of uncomplete intermittent
compression has been clearly described by
Aboulker et al. , who have performed a detailed
evaluation of the caval system in chronic unexplained
myelopathies. They have found with a high frequency
multiple venous abnormalities, and claim that several
major anomalies in the same patient result in chronic
stasis of the perirachidian venous plexi, which might
be responsible for the medullary disease .
Among these venous abnormalities, one of the
most frequent is precisely the extrinsic compression
B. Bok et al.: Jugular Venous Reflux 65
of the left innominate vein, which may be wedged
against the sternal notch by an atheromatous aortic
arch or its most anterior branch, the innominate artery,
as shown by phlebography and arteriography