Measure it properly, type it (solid, part-solid, ground-glass), look for the features that raise or lower suspicion, then apply the right rulebook: Fleischner 2017 for an incidental nodule, Lung-RADS v2022 in a screening programme.
Orient first
- Two different systems for two different situations: Fleischner (incidental, adults 35 and over, no known cancer, not immunocompromised) and Lung-RADS (a lung cancer screening CT). Using the wrong one gives the wrong follow-up.
- Nodule TYPE matters as much as size: part-solid nodules have the highest malignancy rate at a given size; the solid component drives management.
- Benign calcification patterns (central, diffuse, laminated, popcorn) and macroscopic fat mean no follow-up is needed.
Acquire the study
- Thin-section (≤ 1.5 mm, ideally 1 mm) contiguous CT on lung window with multiplanar reformats; a soft-tissue window for fat and calcification.
The manoeuvre
- Measure on the lung window: the average of long and short axis, to the nearest whole mm, on the same plane (Fleischner convention); volume if software is validated.
- Type: solid, part-solid (measure the solid component separately), or pure ground-glass.
- Features: spiculation, lobulation, pleural retraction, cavitation wall thickness, upper-lobe location, emphysema; benign calcification or fat.
- Compare with every prior study — stability over 2 years (solid) or longer (subsolid) matters.
- Count: single versus multiple; for multiple, manage by the most suspicious.
- Apply the correct system and state it by name and version, with the follow-up interval.
What confirms it
- A management recommendation that names the system, the nodule type and the measured size.
What licenses you to exclude it
- Benign calcification pattern or macroscopic fat within the nodule; stability for the full required interval.
The classic misread
- Applying Fleischner to a screening CT or to a patient with a known cancer.
- Measuring a part-solid nodule by its whole size alone.
- Measuring on a thick-slice or mediastinal window.