Most adrenal growths respond marvelously to surgery by a ferret
knowledgeable vet.  You can find a LOT of info which will reassure you
by using:
 
http://fhl.sonic-weasel.org (FHL Archives)
http://listserv.cuny.edu/archives/ferret-search.html (FML Archives)
http://www.ferretcongress.org/CriticalLinks.html
http://www.trifl.org/medical.html
http://www.fothferrets.com/ferretinfo.html
http://www.ferretcentral.org
 
It's never fun and surgery is always scary, but except in the rare cases
where there is lymphoma or carcinoma there, or the also rare cases where
adenoma spreads (it usually doesn't before surgery can be done) the
surgical approach is usually curative.  Luckily most are hyperplasia.
Surgery then restores quality of life and prevents the discomfort and
even pain, as well as avoiding the dangerous complications which can
result without correction.  Of course, always have pre-surgical testing
to make sure that there isn't a problem like anemia present, and always
do pathology on the specimens.
 
There is also a lot of progress being made on medical approaches for
those who aren't surgical candidates.  A search in the FML Archives
http://listserv.cuny.edu/archives/ferret-search.html
for posts with "JM from FHL" in the subject line will bring up a huge
amount of info on that.
 
It also always pays to read up on post-surgical care (no climbing,
newspaper for litter, avoiding any physical stress, stitch pulling (by
others, or by self), etc.  We all forget things between surgeries and
those write-ups help.
[Posted in FML issue 4369]