Sometimes very, very odd things happen.
Today I did a spay on a normal, healthy, happy puppy that I have been seeing for the last couple of months for routine preventative care. All of the pre-anesthetic blood tests were normal and we proceeded with the surgery. When we first go into an abdomen on a spay, most vets "fish" inside using an instrument called a spay hook (also sometimes called a snook hook). The purpose of the instrument is to gently hook around the uterus and pull it out of the belly so we can work with it. Using this hook allows us to make a smaller incision than we would need if we explored the abdomen with our fingers. It's not uncommon to have difficulty finding the uterus, especially in a small pet. The uterus itself can be pretty small, and we're searching among all of the other abdominal organs. However, most of the time I can find the uterus within five minutes or so.
But not today. We're taught to start on the right side to avoid accidentally snagging the spleen and potentially tearing it. I fished, and fished and simply could not find it. In case like this I normally extend the incision slightly to allow me to reach in with my finger and try to feel for it, a trick that normally works well. Again, not so in this case. I was getting pretty confused and worried, so I extended the incision more to explore the abdomen better. At one point I thought I found part of the uterus with a cyst on it, but there was something very strange about the anatomy since I kept searching. After doubling the length of the incision I was finally able to locate the left horn of the uterus.
Let me pause here to give a brief anatomy lesson. A dog's uterus is a bit different than a human's. The uterus is Y-shaped, with the "body" being the main part of the uterus and each arm of the Y called "horns". The ovaries are at the end of each horn, and puppies develop in the horns. When we spay a dog we ligate at the ovaries and then at the uterine body, removing the uterus entirely. Here's an image showing what I'm talking about....
So I found the left horn and ovary and everything looked okay. I traced it back to the cervix, and normally when doing so I'll find the bifurcation leading to the opposite horn. Nope. Nothing there but some blood vessels and connective tissue. I extended the incision further and started digging around where I thought I found the other uterus. As I looked around more, I found what appeared to be an abnormally shaped ovary and a little section of uterus, though not in the normal place. I followed the connective tissue and ended up at the other horn.
This is a rare condition, but it can happen. Part of the uterus doesn't fully develop or doesn't develop at all. In 14 years of practice and a couple of thousand spays (literally), this is only the second time I've seen this happen. In cases like this we remove the identifiable tissues and proceed relatively normally. Because there is already abnormal anatomy, we cannot rule out the possibility of pockets of ovarian tissue that develop unconnected to the rest of the reproductive tract, which I warned the owners of. However, usually in cases like this it's an incidental finding and the dog does fine afterwards.
It's pretty true that you never know what you're going to face on any given day as a vet.