I am sure that there will be many responses to this one, but just in case I
thought I would throw my own in since I just went through the same thing
with my Kali.
 
Most likely it is the sign of adrenal gland disease, although fragments from
an incomplete spay can also cause it (since your ferret has the tattoos, she
probably already has been spayed).  You didn't mention an age for your
ferret, but I was told by the vet that treats all of the local shelter
ferrets that since mine was over two years old the possibility of it being
caused by an incomplete spay were slim to none as she would have shown signs
earlier.  She recommended proceeding immediately with surgery to "check out"
the situation.
 
I did my own research and everything I found confirmed what she was saying.
I asked about testing to be sure that really was the problem and she told me
that in marginal cases it might help, but she said in my case there was no
need for it even though the swollen vulva was the only symptom.  She said
that alone was enough evidence and surgery was the only recommended
treatment (there are some drugs being used to treat this disease, but from
what I have read, they are usually only used in ferrets that aren't good
surgical candidates due to other illnesses or age).  I also got a lot of
good information from the FAIML and from other ferret owners that confirmed
all of these things.
 
Needless to say, I had the surgery done (by my own vet and not the one I
had the consult with) and it was the left gland.  The lab results showed
adenocarcinoma.  I would like to add however that when we did the surgery,
neither gland looked bad.  There were no signs of enlargement,
discoloration, and no obvious difference in texture in either gland.  We
took the left one anyway because I had read and been told you don't ever
come out empty handed in a case like this.  It has now been 3 weeks since
the surgery, and Kali's vulva has just started to retain its normal size.
It's still a little bit swollen, but nothing compared to what it was.
 
I hope this helps you!
 
Stacia
[Posted in FML issue 2379]