Mark,
    Subsequent to the publication of Biology & Diseases of the Ferret, by
James G.  Fox, DVM (the source you cited), additional information concerning
the disease you described has been published.  We now know that ferret
adrenal hyperplasia or neoplasia is not the same as Cushings.  If you
haven't done so already, please download the Ferret Adrenal Disease FAQ
(which IMHO should be required reading for every potential/actual ferret
guardian!)
 
    Regarding the pre-opertative examination of the adrenal gland(s), your
vet **might** be able to palpate the gland(s).  Ultrasound, which you
mentioned, and bloodwork, are additional aids to diagnosis.  All of the
aforementioned methods were successfully employed with several of my ferrets
who presented as having "classic" signs of adrenal disease.  One of them was
also found to have insulinoma.  Each subsequently underwent surgery and were
thus able to again enjoy life :-)
 
    Yet another ferret I had presented as suffering from hepatic (liver)
involvement.  Briefly, I requested the vet consider using ultrasound to
assist her making the diagnosis.  I did this because Stretch's physical
condition had rapidly deteriorated to the point I worried that he might not
tolerate exploratory surgery; too, the findings would determine the
treatment plan.  Without going into details, I (and the vet) were thankful
this option was selected because exploratory surgery would have only caused
him pain.
 
    Perhaps the vets on this list will shed light on the issues you raised.
Their postings on this list are no doubt highly valued by all of us.
     Irene & Kids
[Posted in FML issue 1327]