Two approaches to management
Today, the evaluation of pulmonary nodules is based on two authoritative guidelines: the Fleischner Society (Fleischner Society, 2017) and the British Thoracic Society (BTS, 2015).
- Scope: The Fleischner recommendations are designed for incidentally detected nodules in patients over 35 years of age. The British guidelines cover all nodules in individuals aged 18 and older.
- Measurement methods: The Fleischner Society suggests averaging the short- and long-axis diameters. The BTS insists on using volumetry (determining the exact nodule volume in mm³). Diameter assessment in the British guidelines is a fallback option when volume calculation is not feasible.
- Risk stratification: Fleischner uses a simplified division into high (≥5%) and low (<5%) risk. For larger nodules, BTS recommends calculating the probability of malignancy using precise statistical models (the Brock model and the Herder model after PET/CT).
Size and growth rate
Size is the dominant factor when choosing further management. Most benign lesions have a diameter of less than 2 cm.
- Threshold values: Nodules under 5–6 mm (or with a volume up to 80 mm³) typically do not require follow-up imaging, as the chance of finding cancer in them is minimal.
- Significant growth: According to Fleischner criteria, this is an increase in diameter of at least 2 mm. The British guidelines consider a volume increase of more than 25% to be significant.
- Volume Doubling Time (Volume Doubling Time, VDT): If a nodule grows rapidly and its VDT is less than 600 days, this is a red flag. The exception is indolent adenocarcinomas, which can grow extremely slowly.
CT morphology: distinguishing benign from malignant
In addition to size, the appearance, margins, and internal structure of the lesion play a critical role.
- Shape and margins: Smooth borders are more common in benign lesions, but this sign is unreliable. Lobulated margins are suspicious, and spiculated (spiculated) margins are a reliable predictor of malignancy. Concave borders on all sides or a flat surface adjacent to the pleura favor benignity.
- Internal structure: The presence of central air bronchograms (air bronchograms) or the soap bubble sign (soap bubble lucency) is characteristic of adenocarcinoma due to its lepidic growth pattern.
- Calcifications and density:
- Laminated or dense central calcification is a sign of a prior granuloma.
- Popcorn-like calcification combined with fat density is the classic picture of a hamartoma (hamartoma).
- Intrapulmonary lymph nodes: Appear as small perifissural oval or triangular nodules located close to the pleura and often connected to it by a thin strand. They do not require follow-up, as they never transform into cancer.
Subsolid lesions
A special category consists of subsolid nodules (Subsolid Nodules). They are divided into two groups:
- Pure ground-glass nodules (Pure ground-glass nodules): localized areas of increased density through which normal pulmonary architecture remains visible.
- Part-solid nodules (Part-solid nodules): contain a dense solid component that obscures vessels and bronchi.
Subsolid lesions may represent precancerous lesions, such as atypical adenomatous hyperplasia or adenocarcinoma in situ. They are characterized by pure lepidic growth without solid components. If such nodules persist or a solid component begins to develop within them, surgical resection is considered. If the picture remains stable, monitoring can continue for 4–5 years.
Briefly: answers to topical questions
At what sizes and characteristics of a pulmonary nodule is PET/CT indicated?
PET/CT should be considered for large solid nodules measuring greater than 8 mm or with a volume greater than 250 mm³ according to the Fleischner Society guidelines; alternatives include follow-up CT at 3 months or biopsy. According to the British Thoracic Society guidelines, PET/CT is indicated when the malignancy risk is 10% using the Brock model.
What is the radiation monitoring strategy when multiple pulmonary nodules are detected?
The radiation monitoring strategy for multiple pulmonary nodules depends on the clinical guidelines used and is determined by the characteristics of the largest lesion.
| Guidelines | Management strategy for multiple nodules |
|---|---|
| Fleischner Society (Fleischner Society) | CT at 3–6 months, then consider CT at 18–24 months. The strategy is dictated by the largest nodule. |
| British Thoracic Society (BTS) | No separate guidelines. Risk assessment is performed using the Brock model, which takes into account the number of nodules. |
The duration of follow-up for stable multiple subsolid nodules on CT is also dictated by the largest nodule.
To memorize the CT signs of early adenocarcinoma, use the mnemonic: Ground-glass opacity, Slow growth (high VDT), «Soap bubble» sign (lepidic growth).
Class and exam questions
Is follow-up necessary for a 4 mm nodule?
Generally, no. According to both guidelines (Fleischner and BTS), small foci up to 5 mm are extremely rarely malignant and do not require follow-up unless the patient has other indications.
What is a perifissural nodule?
This is an intraparenchymal lymph node located near an interlobar fissure or pleura. On CT, it has an oval shape and a thin band extending to the pleura; it is considered entirely benign.
Why is it necessary to calculate volume doubling time (VDT)?
This parameter allows for an objective assessment of growth aggressiveness. A VDT value of less than 600 days indicates a high probability of a malignant process and requires active intervention.
What else to study on this topic
- Mathematical models for malignancy risk assessment (Brock, Herder)
- Principles and protocols of volumetry in multidetector CT
- Differential diagnosis of ground-glass opacity lesions
- Organization and efficacy of low-dose CT lung cancer screening programs
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