Vet Talk

X-rays are Black and White but they aren’t Black and White

An X-ray is uncertainty made manifest

Published: June 08, 2015

Photo by Dr. Teri Ann Oursler

We all need to expand our minds a little.

I’m not talking 60s-style mind alteration, complete with flower stickers and creative pharmacotherapy. I’m talking about our tolerance for uncertainty. Specifically, I’m talking about our faith in medical tests, chiefly X-rays.

X-rays are one of those medical advances that are so commonplace as to be almost boring. As advances in imaging such as MRI and PET scans have progressed, good old X-ray now can seem downright folksy and a little retro. But step back for a moment and consider just what you get when your veterinarian takes an X-ray. (Technically, an X-ray is the actual ray of charged particles emitted by an X-ray machine, and the resulting image is known as a radiograph, but for the sake of brevity and levity I’m going to just refer to the image itself as an X-ray.)

When you look at a radiograph, er…X-ray, you’ve just developed the miracle of X-ray vision. Long the staple of those eensy-weensy ads in the back of questionable magazines, X-ray vision lets us check out things inside patients like bones and assorted giblets that are invisible to the naked eye. You can also tell what kind of underwear a dog has on, too (if any). Without surgically opening up a dog or cat, you just can’t see a kidney, a tumor on the spleen, or 34 socks stuck in the intestinal tract. With an X-ray you (sometimes) can. That’s pretty amazing!

The problems all crop up with the parenthetical “sometimes.” It’s not 100% - nothing is in medicine, but X-rays are especially prone to misleading results. An X-ray is uncertainty made manifest. It’s all shadows and way more than 50 shades of grey; rarely is a diagnosis made on an X-ray without a certain degree of self-doubt.

You’ve heard of a cancer scare – in many cases that’s some blurry little blob on an X-ray that someone is worried about. To ignore the blob would be to ignore something that could be important, while to say “that there is definitely badness” is to imbue the humble X-ray with a level of certainty that just isn’t there. We’re left with a head-scratching “I dunno, that just kinda seems off” and the cancer scare begins.

This radiographic uncertainty comes into play all the time. Dogs are like perma-toddlers, always trying to see just how much of the world is edible. Most of the time the inedible stuff passes out the back end of the dog to the amazed stares of their doggy friends and owners alike, accompanied by awed exclamations of “you passed that?!” But sometimes there’s disagreement between the offending item(s) and the intestine, say a length of ribbon or 34 tube socks, and the works get gummed up by a blockage. Food can no longer pass through and mayhem and unhappiness ensue. If the blockage persists long enough, the intestines start to die and leak and infection can spread throughout the abdominal cavity in a condition known as septic peritonitis, which is Latin for “this is really most sincerely not good, old chap.”

Trying to diagnose an intestinal blockage with an X-ray is only one or two steps more accurate than trying to predict crop yields using pig innards. True, in a few cases it’s obvious, usually when the offending object shows up clear as day, something like a rock or metal. Then off we go to the OR to cut out the offending badness. Unfortunately, many things that dogs eat in their quest to consume the universe don’t actually show up on an X-ray because the beam just goes right through them, such as cloth, plastic, rubber, and rope. That means we’ll see Grandma’s wedding ring but not plastic milk rings, tampons, or underwear; we won’t see an eraser but we will see the metal around a pencil eraser. We have to expand our minds a bit (which is much easier in Colorado these days) and try to see where the usual intestinal stuff isn’t. That’s’ right – you have to look for the spot in the intestines that’s missing something you normally see, as that may be where the blockage is. It’s like trying to not think about that thing that you’re thinking about. Here, try it: penguin. Now, don’t think about a penguin. Next: Bea Arthur naked.

We take X-rays because they can sometimes show us the answer, but many pet owners expect X-rays to be a definitive, perfect, and conclusive answer and they just aren’t all that all the time. They are helpful. But with a price tag of sometimes several hundred dollars, pet owners want more for their money than a shrug and downcast eyes.

So when faced with a vomiting dog and an inconclusive X-ray, what do we do? There are a few options:

Thing you can do  Good   Bad
Wait a few hours and take more X-rays, see if things have changed If no changes, that’s better evidence that there may be a blockage

More time, more risk of peritonitis, more money

Abdominal ultrasound Better at finding blockages than X-rays in most cases

Not readily available, can cost more than X-rays, still not always definitive

Exploratory surgery Get the blockage out quickly (if it’s there) Only there about 2/3 times, unless the blockage is obvious, risky, expensive
More X-rays with barium added (barium series) Can help point out the spot where the obstruction is hiding Messy, risk of inhaling barium, not definitive, more money, white poop for a few days (which is actually kinda cool)

When I order X-rays for a dog who has a possible foreign body or a blockage, I always caution the owners that a "normal" X-ray doesn’t rule out the possibility that something is still in there causing problems. Somedays, I feel like there are no normal X-rays, just ones where the problem hasn’t been found yet. I’ve worked on plenty of dogs that had "normal" X-rays on Monday who were having 43* socks surgically removed from their intestines on Wednesday.

Understanding what any medical test can and can’t tell you is getting one step closer to being realistic about how much accurate information medicine can give us. The next time your veterinarian recommends an x-ray, or any test, your understanding that it may not lead to a conclusive diagnosis would be 50 shades of awesome.

*I know – I meant to do that. See how imperfect medicine is?

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