A lung nodule is a spot detected on a chest imaging scan. It is a single, well-defined lesion, ≤ 3 cm in diameter, completely surrounded by air-containing lung tissue.
Lung nodules can be classified as either solid or sub-solid nodules based on their density.
A solid nodule on a CT scan appears as a round or oval white spot in the lung. It is usually dense enough to obscure the bronchi and blood vessels going through it. Sub-solid nodules are known as ground-glass nodules (GGNs) or ground-glass opacities (GGOs). They are subdivided into pure ground-glass nodules (pGGNs) and mixed ground-glass nodules (mGGNs). pGGNs contain no solid components, whereas mGGNs contain some solid components.
A ground glass nodule (GGN) appears as a hazy, ground-glass-like spot on a chest CT scan. It’s less dense than a solid nodule and resembles a faint cloud, often allowing visibility of blood vessels and bronchi within it. Some GGNs may disappear over time, which usually indicates inflammatory or other benign lesions. However, persistent GGNs may signal more serious diseases requiring regular follow-up, including precancerous lesions, in-situ lung cancer, or early lung cancer.
Various conditions can cause GGNs. These may include interstitial fibrosis, pulmonary fungal disease, atypical adenomatous hyperplasia, adenocarcinoma in situ (AIS), primary lung cancer (including microinvasive adenocarcinoma (MIA), invasive adenocarcinoma (IA)) and metastatic lung cancer.
How does a pulmonologist determine if a GGN is benign or malignant? They need to consider some features of the nodule.
- Size
Nodule size, especially the solid component size, is a major diagnostic factor. Generally, smaller nodules tend to be benign, while larger ones are more likely malignant. Follow-up is typically recommended for GGNs > 8 mm to monitor changes in size and density. Conversely, GGNs < 5 mm have a very low probability of malignancy.
- Margin
Marginal features are another important factor. Malignant GGNs often have irregular or lobulated contours and spiculated borders. Lobulation is more often associated with malignancy and requires attention. However, some benign nodules also also exhibit features such as lobulation, burr, etc.
- Density
As mentioned, lung nodules are classified by density as solid or ground glass nodules (GGNs), with GGNs further categorized as pGGNs or mGGNs. Generally, solid nodules often have a lower probability of malignancy. pGGNs have a higher malignancy rate, while mGGNs have a significantly higher probability of being malignant.
- Growth rate
Rapid growth is a typical characteristic of malignant tumors. Therefore, a faster growth rate in a GGN indicates a greater risk of malignancy.
In short, it’s important not to panic if a ground glass lung nodule is detected. This is because GGNs, especially small ones, are unlikely to be malignant.
However, since some GGNs may represent or develop into significant disease, regular monitoring and follow-up with a specialist are recommended to determine if treatment is necessary.