Common Knowledge About Pulmonary Nodules (Part 1)
With the widespread adoption of thin-slice CT scanning, more and more people are found to have one or multiple small pulmonary nodules during routine physical examinations. Statistics show that among adults undergoing active screening, about 40% have small pulmonary nodules reported on their checkup reports. Yet only about 3.6% of small pulmonary nodules are malignant—that is, what we commonly call lung cancer. The overwhelming majority of pulmonary nodules are benign.
Other statistics show that among the general population, about 0.7% have pulmonary nodules, of which 7%–8% are malignant. So pulmonary nodules are a very common finding, but only a minority are malignant; the vast majority of clinically diagnosed pulmonary nodules are benign.
Nevertheless, because lung cancer incidence is currently high in our country, with over a million new cases every year, and because lung cancer has the highest mortality rate of all cancers, many people become anxious after discovering a small pulmonary nodule on a checkup and consult doctors about how to handle it. In my daily practice I receive a large number of consultations about pulmonary nodules, so I am writing this article to introduce some common knowledge about them.
First, a pulmonary nodule is not the same as lung cancer. Infectious granulomas (bacterial, tuberculous, and fungal), intrapulmonary lymph nodes, focal inflammatory pulmonary fibrosis, atypical adenomatous hyperplasia, pulmonary hemorrhage, silicosis, miliary tuberculosis, hamartomas, lipomas, neurofibromas, and sclerosing hemangiomas can all form small nodules in the lung. Such nodules are benign pulmonary nodules and need not be treated as lung cancer.
Generally, the best way to distinguish benign from malignant pulmonary nodules is pathological examination. Determining whether a nodule is benign or malignant by needle biopsy can reach about 90% accuracy; determining it by surgery can reach essentially 100% accuracy. But puncture and surgery are both invasive, so not everyone found to have a pulmonary nodule needs this kind of differentiation.
Doctors classify pulmonary nodules into low-risk, intermediate-risk, and high-risk types based on the nodule's location, size, shape, and characteristics, and manage patients of different types differently. Low-risk patients have a repeat CT once a year for three consecutive years of observation. Intermediate-risk patients are rechecked at three months, six months, and one year, and thereafter once a year for three consecutive years. High-risk patients need needle biopsy or surgery for pathological testing to determine the nature of the nodule; if it is malignant, treatment should begin as soon as possible.
During observation, benign and malignant pulmonary nodules are generally distinguished by the volume doubling time (VDT). The VDT of a malignant pulmonary nodule is usually 30–400 days. That is, within 30–400 days, most malignant pulmonary nodules double in volume or more. If a patient's small pulmonary nodule doubles in volume within less than 30 days, it is more likely an infectious benign nodule; if a pulmonary nodule changes little over 400 days of observation, it is generally benign. Nodules that show little change over 400 days can thereafter be monitored periodically without urgent intervention. However, this observation may be lifelong, because some benign nodules can still undergo malignant transformation. Some benign pulmonary nodules also disappear spontaneously during observation, in which case the patient need not be observed for life.
For patients with tiny (micro) nodules, even if malignant, the nodule does not progress rapidly during observation. After observing for three months, six months, and one year, if malignancy is likely, then medical intervention is undertaken; the patient's prognosis is essentially no different from if it had been treated before observation. Therefore, if a tiny pulmonary nodule is found on a checkup and the doctor advises observation, one can observe patiently without rushing to intervene. There is also no need to undergo CT too frequently, because CT radiation is harmful to the body.
Of course, if the patient has a family history of tumors, an affected proband in the family (i.e., a family member with cancer), a long smoking history (especially if smoking began before age 20), or a high-risk occupation associated with lung cancer (such as marble cutting, mining, or cooking), then after a pulmonary nodule is found, heightened attention is needed. These patients can receive some treatment: if an infectious factor is present, anti-infective drugs are used and changes in nodule size are observed. If no infectious factor is present, symptomatic treatment may be given in moderation, or no treatment at all, with periodic observation.
Pulmonary nodules vary in shape and nature and are generally of three types: part-solid (semi-solid) nodules, ground-glass opacity nodules, and solid nodules. Among these, part-solid nodules have the highest likelihood of being malignant, ground-glass opacities are next, and small solid nodules are least likely to be malignant. However, this does not mean that small solid nodules can never be malignant. Other factors must also be considered to determine the risk of a pulmonary nodule.
(To be continued)