Wow. I am amazed that this is your first chicken health issue in 18 years. Well done!
Thank you!

Well, only my first internal organ issue for hens. Lots of wounded hens/roosters (my very first chicks were 4 males and only 2 hens)

. We live on an acre, but I had to re-home "the boys" (because of neighbors too close - we are the only acre property) - Just for a laugh -- we knew our neighbors were fed up, when we would come home and they would start crowing (really - are you humans with voices? Can't you just say, your roosters are really bothering us???).
Anyway I soon found real homes for the roosters (not for food - because I am a raised in the CA bay area and a total city girl)and added in new hens.
But, in the beginning years as we live across the street from a greenbelt, and we had a lot of raccoon/possum raids, then a persistent and wiley coyote for 5 years. And had some local dog raids which massacred our hens and ducks.
My approach is to trap the wild animalsand find them a new area to live in outside of the Bay Area, but I could not catch that coyote. I think I lost about 25 hens over that time frame.
Physical external wounds have been pretty easy for me because of feral cat rescue, owning horses and sick dogs and 2 wonderful vets, that were both friends and lots of issues. But both my friend vets have both passed - one very young and another older vet mentor, both from cancer (they were large animal/farm vets). I sadly miss them both greatly. Wildlife animal rescue helped me gain experience when I was younger (birds, squirrels). This enabled me to help a lot of my hen/rooster issues...broken legs, external wounds.
But this is entirely new for me, and I have learned a lot. I hope I am able to pass it on. This site has been fantastic and very helpful. Though I have been a member and visited occasionally, I had not been active in discussion.