I am so sorry for your loss. I have to agree with Jocoyn it sounds like hemangiosarcoma.We lost our 12 and half year old GSD Daisy to it. As Courtney said the only true way to know is a necropsy. We lose to many of our beloved breed to this dreadful killer. Again my condolences.
Lucky- GSD Rescue 2/16/2002
Thunder : adopted 1/25/2013
Miss Chevy Cruz - 1/25/2013-1/29/15