Lung nodule

A lung nodule is, first and foremost, a finding: something that shows up on an imaging study, the kind of test that takes pictures of the inside of your body. A solitary pulmonary nodule is an opacity, meaning a spot on the image. It's rounded with sharp edges, smaller than 3 cm, and surrounded on all sides by lung parenchyma, the lung's own tissue. Often nobody was looking for it. It just turns up on a scan that was done for some other reason.

So how does one form? Its pathophysiology, meaning the way it comes about, depends on the cause. Sometimes a group of cells changes and starts growing in one particular spot. That growth can be influenced by genetic mutations, which are changes in a cell's instructions, by things in the environment, and by the immune response, the way the body's defenses react. Other times, the nodule is simply the scar left behind by an infection that's already over.

And here's the key point: most nodules are benign, which means they're not cancer. Even so, the possibility of a malignant tumor is always a concern, and without a biopsy, which means taking a small sample of the nodule to study it, telling benign from malignant can be difficult. Picture a small round stone in a photo of a lawn: you can see it's there, but just by looking at the photo, it's hard to tell what it's made of.