Marian Simka et al. elegantly suggest the possible explanation for the positional change of intracranial dural venous outflow, lacking in our published study . They hypothesized that abnormally stenotic valves preferentially formed in the left internal jugular vein might cause the positional alterations of the dural venous outflow. The hypothesis seems fascinating but should need further verification in a sufficiently large population. While, morphological valves have been identified in the intracranial dural sinuses and ophthalmic and facial veins [1, 3, 4]. Although these valves are commonly not visualized on currently available modalities, they can affect the venous outflow at positional changes. Anyway, the authors have successfully provided a useful framework for future studies in this field.
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