The spleen you are describing does sound enlarged.  The spleen can
be enlarged from several things.  The most common reason is called
extramedullary hematopoiesis.  This is a fancy term for the spleen making
red blood cells.  The second most common thing is cancer (especially
lymphoma).  The third most common thing is called hypersplenism.  After
these, the list includes bacterial infections, viral infections (especially
Aleutian Disease), heart disease, anemia, etc., etc.
 
Since you have both enlarged lymph nodes and an enlarged spleen, it is
suspicious for lymphoma.  I would recommend a splenic aspirate or biopsy,
and a lymph node aspirate or biopsy.  If the aspirates are normal then I
would do a biopsy of the lymph node(s).
 
Yes, ferrets do fine after their spleen is removed.
 
Hope that helps,
Jerry Murray, DVM
[Posted in FML issue 3432]