Necropsy - warning graphic photo included help needed to narrow down cause

[H3xan01c]

Greetings,
I have been raising chickens since April (2014) not long. I purchases 17 sexlinks (now 2yrs old) from a boy up the road, a family I know. This weekend I found a hen dead in the afternoon. My first realization that I need to band their legs so I can identify the chickens better. So I could know if this was the "broody" one in the nesting box at night, or the sleepy one that was napping in the yard during the day.
I felt I had to open her up and determine how she died as there was no wounds visible. I started by removing feathers to look for wounds. I have not opened up a a healthy chicken yet so while I have researched online I can only speculate on what the cause of death was. I think the large yellow dough like thing is a tumor? the gullet was dark, black and I believe it should be pink/red the interior of that was dry and didn't seem right to me. there is also a white mass that I have not identified.
She also seems rather thin. I was thinking possibly a tumor blocked the gullet, blocking and drying it out and starving the poor hen.

If anyone can help it would be appreciated.

 

[Firekin1]

where did you find the yellow mass? I have found that in hens suffering from egg peritonitis.

 

[H3xan01c]

I found the large yellow mass just as I started in the rear near the cloaca. It was very pliable like a yellow plumber putty.

 

[H3xan01c]

and it did look like cooked egg yolk, and I dismissed that originally as silly; but from a little reading on what you mention I see it may have been just that, egg yolk.