Primary differential cont'd

So...yes, cancer was my first differential.

I discussed this with the owner. I told her that I could not explain exactly where the small clusters of bacteria were coming from. My guess was that there was likely GI cancer that was causing leakage of the GI tract.

That was where I made the mistake. If you've ever read any of Atul Gawande's books (Complications and Better)- you'd probably be familiar with this mistake. I assumed that my primary differential was the right one - based on previous experiences. I did make sure - however - to tell them that I wasn't sure - and that the next step would be abdominal ultrasound or exploratory laparotomy.

They elected to euthanize, and because I am always, always trying to learn and improve, I requested a necropsy. The owner consented.

When I opened the abdomen, the omentum was so diffusely inflamed and erythematous that I was quite astounded. There was fibrin floating around in fluid (quite a bit of it). I examined the intestines and found nothing grossly out of the ordinary. I pulled the stomach out and found the omentum adhered to the pylorus. I pulled it away and stomach and upper small intestinal contents spilled into the abdomen. There was a hole in the pylorus about the size of a quarter. I cut over the hole with a scalpel and out popped a wood chip. I stared, amazed. The dog - instead of having cancer - AT THIRTEEN YEARS old - had a FOREIGN BODY. It had led to necrosis and perforation of the pylorus. The reason the bacterial numbers in the abdomen were so low was because the perforation was an upper-GI one - there is very little bacteria in the stomach/pyloric region - especially compared with the small intestines. Those unusual cells I was seeing were reactive mesothelial cells (reactive due to the abdominal inflammation/peritonitis).

I called the owner and let her know - feeling terrible. I had let my certainty that the dog had cancer cloud my judgment and clinical knowledge. The dog had peritonitis with some free bacteria - that screamed GI perforation. Unfortunately, I thought the perforation was secondary to cancer. It was not.

On the other hand, the dog was 13, had a whomping heart murmur, was very, very sick, and needed abdominal surgery, which the owners had already said they wouldn't go put him through.

But still. It was a vital, vital reminder to watch for the Red Herring (capitals courtesy of a friend) and to always, always remember that differentials are just differentials until you hold the answers in your hand! A 13 year old dog is certainly capable of a foreign body, just as a 1 year old dog is certainly capable of having cancer.