What counts as a nodule
A pulmonary nodule is a small, roughly round spot of increased density in the lung, by convention up to about 3 cm across; anything larger is called a mass and is treated more seriously. A single one with normal surrounding lung is a solitary pulmonary nodule. They are extremely common — picked up incidentally on a CT done for some other reason, or deliberately found by low-dose CT screening in smokers. The vast majority are benign: old infections, small scars, or harmless lumps.
What raises or lowers concern
- Size: Risk climbs with diameter. Tiny nodules under ~6 mm are very rarely cancer; the larger the nodule, the more attention it earns.
- Growth over time: This is the most useful single clue. A nodule that is stable for two years on CT is very likely benign; one that grows is suspicious. Old films are gold.
- Edges and density: Smooth, well-defined, or densely calcified nodules tend to be benign. Spiculated (spiky) edges and persistent ground-glass components raise concern.
- Patient risk: Age, smoking history (in pack-years — though use the catalog link smoking), prior cancer, and certain exposures shift the odds. The same spot means different things in a lifelong smoker versus a young non-smoker.
These factors feed published guidelines that recommend, for any given nodule, one of three paths: no follow-up, interval CT surveillance, or further work-up. Further work-up may mean a PET-CT to gauge metabolic activity, a transbronchial biopsy or needle sample for tissue, or referral toward surgery when suspicion is high. Crucially, slow-growing or pure ground-glass nodules can fool PET, so imaging and biopsy choices are tailored, not automatic.