Tell me to what you pay attention and I will tell you who you are.
-Jose Ortega y Gasset

The senior resident hauled our little band of medical students down to the radiology file room. As he dug through the heavy manila x-ray jacket searching for films, he told us the patient’s story. “This 63-year-old lady was really sick when she came in. Heart attack a couple of years ago. New trouble breathing. Swollen ankles. She was miserable. She was in the ICU for over a week.”

He slid one x-ray after another from the jacket, searching for the chest x-rays that had been taken with a machine rolled to her bedside in the intensive care unit each morning.

“Aha! Here they are!” He snapped the films up onto a series of light boxes and pointed to the one on the left. “Okay, students. This is the chest x-ray from the emergency room the day she was admitted. What do you see?”

We were on our first hospital rotations. We had a pretty decent understanding of anatomy, biochemistry, and pathology, but knew little about clinical medicine. We stared at the x-ray and said nothing.

“Okay, people. Look closely. Describe what you see.”

“Well,” said the bravest among us, “the lungs are here. Here are the ribs and the spine. Here is the heart and the blood vessels. Oh, the diaphragm is down here.”

“Good, good. That’s a start. So what do you see that is different from a normal x-ray?”

This was tougher because we had so little experience with either normal or abnormal images. We stared blankly.

“C’mon. The radiologist has left you some clues. What do you see?”

We leaned in close. At the edge of the lungs near the diaphragm, someone had drawn red pencil marks on the film, pointing out several short parallel lung markings. “Those red wax marks, my friends, point to some Kerley B lines, named after the Irish radiologist Sir Peter Kerley. The lines are seen most commonly in congestive heart failure. They disappear as the failure clears up.”

We looked at the series of chest x-rays and, indeed, the lines resolved as she improved. The resident spent a few minutes describing the radiologic signs of heart failure.

“Okay, students, what lessons did you learn here?”

We repeated back what he had taught us about the x-ray findings in heart failure. We reached into our lab coat pockets for our notebooks and wrote “Kerley B lines = CHF.”

“I learned something else,” said one of the other students.

We all looked at her.

“ALWAYS look for the red pencil marks. If the radiologist was interested in a finding on the film, I should be, as well.”

The chief resident smiled. “Very good! Those marks on an x-ray are a sign of disease as certainly as any clinical finding at the bedside. We call the marks “The Wax Pencil Sign.” Always look for them. They can save your butt in the middle of the night.”

Over the years, light boxes have all but disappeared from hospitals. Voice-recognition software and electronic medical records have made radiology reports available almost instantaneously. Information passes from the radiologist to the treating physicians quickly.

For a generation of physicians, though, The Wax Pencil Sign was a reliable means of communication. It said, “Look right here for the secret.” It helped us when we needed to discern the critical findings in an x-ray.

Not long ago, I ran across a long-forgotten wax pencil in a drawer. Few people remember its use and importance. It makes me wonder about all of the Wax Pencil Signs we depend on today that will be obsolete when our current students finish their careers.

Bruce Campbell is an otolaryngologist who blogs at Reflections in a Head Mirror.