Sunday, March 2, 2008

Radiology Eye for the Straight Guy

"There he is in that thicket -- his ear just twitched!"
My uncle has just described something that I cannot see at all. I look harder, but no joy.
"Look, he's standing up!"
I peer through the scope of my rifle, but still see nothing but distant thicket, about 200 - 300 yards away from us.

Finally the deer bolts from the thicket and heads away from us at Warp 2. At this point, even I can finally see the darned deer. Of course, the butt of a running whitetail deer is only slightly harder to see than a flashing strobe light. For someone who normally takes pride in having sharp vision, I am feeling pretty humble right now.

This happened years ago, just before I headed off to medical school. However, I remember it very clearly, because it was the first time I truly saw the vast difference between what can be seen by a trained eye versus an untrained eye. This was a recurring lesson in med school, whenever one of my professors would make an astute diagnosis from some minor clinical clue I had never noticed.

Nowadays, I spend my workdays interpreting medical images, usually side by side with the medical students or radiology residents I teach. I now possess the same advantage over them that my uncle had over me - decades of practice at training my eye to see tiny details in a sea of noise.

My students still remind me of what it's like to have the eye of a beginner whenever they miss something that seems now seems quite obvious to me. I then get to point out to them the bent blade of grass or the twitching ear that gives away the deer hiding in the picture. Usually, most of my students believe me, and accept this lesson with appropriate humility.

However, sometimes they don't. I was once confronted by an incredulous med student in the middle of a trauma lecture I was giving to his entire second year class. I had just suggested to them that the patient above with knee pain had a fracture of his femur. Before reading any further, take a moment and see if you can spot the abnormalities that they didn't see.
"You can't expect me to believe that you see a fracture on that film!"
Judging from the vocal borborygmi coming from all around the room, his classmates didn't believe me either. Even after I pointed out the subtle X-ray findings, they didn't seem very convinced. At the time, I was somewhat disconcerted by their distrust.

In retrospect, it's not hard to see why they were so skeptical. To them, I was a magician who had walked out on stage with a rabbit in his hand, and was now trying to convince them that I pulled it out of my hat backstage. Why should I expect the trick to work if I didn't first show them the empty hat or my empty hands?

With the benefit of hindsight, what would I say to them now? The French have a great term for this predicament : "l'esprit de l'escalier" (literally "stairway wit") -- the comeback you only think of when it is too late. Here's mine:
I don't blame you for being skeptical. Extraordinary claims require extraordinary proof, and so far, the only evidence you have that I spotted this fracture is my say-so.

Critical thinking is one of the skills we want you to learn here in medical school. I'm glad that you are using it here, and I admire your being courageous enough to voice your disbelief in front of your whole class.

So, you don't have to believe that I spotted that fracture. But please believe this: that an expert observer can spot things that are invisible to a newbie.

As you move from your classroom years to your clinical rotations, you will see this phenomenon again and again. You will see cardiologists finding heart murmurs that you can't hear. You will see surgeons palpating breast masses that you can't feel. And yes, you will see other radiologists spotting fractures that you can't see.

You will also do these things yourself, once you have enough flight time of your own.
At this point, I would again point out the findings that shout "Fracture!!" very clearly to my eye:
1. the tiny discontinuity in the femoral cortex that shouldn't be there

2. the straight line formed by a fat-fluid level in the knee joint -- a handy sign that a bone has broken, allowing marrow fat to leak into the joint

I would also tell them the story of my uncle , and what I learned about reading films from him and the deer.  Even though I didn't realize it at the time, that day long ago in West Texas may have been the first real day of my training as a radiologist.

1 comment:

Vijay said...

Argh!! F***!! I'm disgusted with myself. I saw the obvious fracture on the frontal film but missed the fat-fluid level. Note to self: Remember to see the structures around the area of interest. No. Correct that. Knock (really hard) on my head.