Cyn,
I just got back from the state vet lab after having a Welsumner hen put down and necropsied. She was a little over a year old.
There were similar findings inside my hen. She did not have any sausages inside her abdominal cavity, but she had a mass the size of a baking potato in part of her oviduct, with a few other pieces in other areas of the oviduct.
The vet cut the big mass open and their was a yoke inside with layers of gunk circled around it. It looked like a sliced onion.
Anyway, Dr. Lanires said it was caused by an infection that traveled to her oviduct. She was not an internal layer, as all the infection was in her oviduct.
He said it could have been caused by any type of infection, but he suspected MG (CRD). He did a culture to find out exactly what it was and if it was anything I need to treat my others for. He also asked if I wanted an AI test, and I said yes.
I hate to butt into your post, but it sounds like my hen and Lorelei may have had a similar problem, and maybe others can learn from our experiences.