In recent years, with the development of imaging techniques and equipment, especially the popularity of multi-layer spiral CT, the detection rate of pulmonary nodules has increased significantly. Therefore, the clinical management and decision making of pulmonary nodules is gradually becoming one of the problems that plague clinicians. (Surgical treatment? Non-surgical biopsy? Continuous CT scan for close follow-up?)
In addition to determining the risk of benign and malignant based on imaging features at the initial diagnosis and selecting further investigations, follow-up is commonly used. What tools to use for follow-up, how often to follow up, and how long to monitor the follow-up is a very important practical issue in clinical work.
To facilitate clinicians to grasp the management of intrapulmonary nodules, I have reviewed the following information and would appreciate any inappropriate corrections.
Guidelines.
As early as 2005, the Fleischner Society guidelines were introduced in the United States, focusing on follow-up and management strategies for patients older than 35 years of age with small pulmonary nodules without known malignancy, and have been used to date.
In 2013, the American College of Chest Physicians (ACCP) published the 3rd edition of its clinical management pathway guidelines for single or multiple pulmonary nodules.
Combining the above 2 guidelines, a simple and feasible protocol in clinical practice is described for the reference of our colleagues.
Definition.
The currently accepted definition of a pulmonary nodule is a well-defined, imaging-opaque, solitary or multiple pulmonary nodule ≤75 px in diameter, completely surrounded by air-containing lung tissue, without pulmonary atelectasis, hilar enlargement, or pleural effusion. It can be a solid, subsolid nodule (pure ground glass nodule, partially solid nodule). Pulmonary nodules ≤8 mm were defined as sub-centimeter nodules, and lesions >3 cm in diameter were defined as pulmonary masses rather than nodules.
And of these nodules, the diagnostic difficulty is often parenchymal diameter lesions below 25 px.
Clinical management-imaging evaluation
When the presence of a pulmonary nodule is identified on a patient’s chest CT examination, the same area of the patient’s previous CT images needs to be reexamined. Information on the size and characteristics of the nodule is important for the determination of benignity and malignancy as well as for the development of a subsequent treatment plan. The results of the study showed that subcentimeter nodules were less malignant, regardless of whether they were solid or subsolid nodules. Lung nodules with burrs or irregular borders were 5 times more likely to be malignant compared to those with smooth borders; those with pleural depression signs were 1 times more likely to be malignant; and vascular signs and lobarization increased the probability of malignancy by 70% and 10%, respectively.
Imaging features of benign nodules
Dense, uniform calcification is a reliable feature of benign nodules. (Other features 1. laminar calcification 2. central calcification 3. popcorn-like calcification- 1 and 2 are commonly seen in infected nodular lesions and 3 is a typical change in malignant nodules. ) Polygonal nodules in the lungs with a 3D ratio greater than 1.78 are diagnosed as benign pulmonary nodules with a sensitivity of 61% and a characteristic of 100%. Other benign features: nodules distributed in bunches with a spacing of less than 10 mm can suggest a benign diagnosis (infectious)
Imaging features of malignant nodules
In a retrospective study of lung cancer nodules, the frequency of burr and lobar signs was found to vary from 33% to 100%, while 50% of nodules with regular, well-defined margins were malignant. The presence of ground glass is thought to increase the likelihood of malignant nodules being diagnosed.
Characteristics of malignant nodules
1. Vacuolation: multiple smaller translucent areas within the nodule (scaffolds of lung structures that have not been destroyed by cancerous tissue)
2.Cavitation (or cavity): ischemic necrosis of tumor tissue
3. pseudocavitation (teardrop-like or spherical air-dense areas appear in 50% of alveolar cell carcinomas; it is also a feature of metastatic adenocarcinoma, whose histological features show a significant expansion related to bronchial tissue)
Some studies have shown that 80% of malignant nodules exhibit one or more of these features
Marginal features: burr, lobulation, etc.
In conclusion, the imaging features of malignant nodules are variable and must be taken seriously and treated as malignant nodules whenever they do not have the characteristics of a clearly benign nodule.
Clinical management pathway – solid pulmonary nodules
Solid pulmonary nodules ≥8 mm in diameter: The first step is for the clinician to determine the patient’s surgical risk, the probability of malignancy of the nodule, and the PET scan evaluation. The Mayo Clinic model estimation method is the most widely used of the available methods.
Mayo Clinic model
This model calculates the probability of malignancy of a pulmonary nodule based on six independent risk factors (age, smoking history, history of extrathoracic neoplasia, nodule diameter, burr sign, and nodule localization), according to the formula
Malignancy probability = eX / (1 + eX,, X = a 6.827 2 + (0.039 1 × age, + (0.791 7 X history of smoking, + (1.338 8 × history of tumor, + (0.127 4 × nodule diameter, + (1.040 7 × burr sign, + (0.783 8 × localization,.
Explanation of the formula: e is the natural logarithm; age is calculated numerically; if there is a history of previous smoking (whether or not it has been quit, then 1, otherwise 0; if within 5 years (including 5 years, there is a history of extrathoracic tumor then l, otherwise 0; nodule diameter is calculated in millimeters; if there is a burr at the nodule margin then l, otherwise 0; if the lung nodule is localized in the upper lobe then 1, otherwise 0.
For example, in a 60-year-old patient with a history of previous smoking and no history of extrathoracic neoplasia, a 20-mm nodule with positive marginal burr is found in the upper lobe on CT. The X calculated by the formula is 0.683, giving a 66.4% probability of malignancy of the nodule.
Solid pulmonary nodules <8 mm in diameter: The 2013 ACCP 3rd edition guidelines are consistent with the 2005 Fleischner Society guidelines for follow-up of small solid nodules.
That is, the timing and interval of CT surveillance follow-up is determined by the size of the lung nodule, the patient’s age and smoking history, and other risk factors for lung cancer.
Clinical management pathway-subsolid pulmonary nodules
1. For pure ground glass lung nodules ≤5 mm in diameter, follow-up is usually not required.
For pure ground-glass lung nodules 5-10 mm in diameter, CT should be reviewed once a year for 3 years.
For pure ground-glass lung nodules >10 mm in diameter, review 3 months after the initial CT examination, and if the lesion persists, non-surgical biopsy or surgical treatment is recommended unless the patient cannot tolerate surgery
2. For partially solid pulmonary nodules ≤8 mm in diameter, CT scans should be performed at 3, 12, and 24 months after the first examination for strictly regular follow-up, and CT should be repeated once a year for 3 years thereafter.
In case of enlargement of the solid portion during the follow-up, non-surgical biopsy or surgical treatment should be performed immediately. For partially solid pulmonary nodules >8 mm in diameter, CT needs to be repeated 3 months after the initial examination, and if the lesion persists then PET scan, non-surgical biopsy, and surgical treatment should be actively managed.
For subsolid pulmonary nodules >15 mm in diameter, no review of CT is required and active management is directly performed.
It is believed that with the development of examination techniques, the differential diagnosis of small intrapulmonary nodules will become more favorable.