They serve as a reminder that medicine is not just about biology; it is about observation. It is about the ability to look at a grainy black-and-white image and see the invisible physiology at work—the struggling heart, the rising pressure, the seeping fluid.

The result on the film is a white line.

The presence of Kerley B lines on a chest X-ray is a significant finding, as it indicates:

Imagine the lung not as a balloon, but as a wet sponge. The "scaffolding" of this sponge is the interstitium—a network of connective tissue that houses the lymphatic system, the blood vessels, and the structural support for the air sacs (alveoli).

Mostly found in the lung periphery , specifically at the lung bases near the costophrenic angles (where the diaphragm meets the ribs).