Wow, have you opened an industrial strength can of worms!  I'd worry less about
what constitutes an ECA stenosis and more about defining an ICA stenosis by the
criteria you shared with us.  I know that you know the pitfalls of this
criteria (no accounting for proximal or distal disease, contralateral disease,
etc.)  I suggest you challenge the interpreting radiologists to put their
references where their mouth(es) is/are and then check your QA track record.  I
 suspect
that something  along the way got lost in the translation.  

Steve Knight, RVT
Fletcher Allen Health Care (UVM)