What causes ground-glass opacity in the lungs?

Nowadays, more and more people are suffering from lung diseases. Most people develop from pneumonia at the beginning, which then turns into lung edema, and finally leads to lung cysts and lung cancer. However, many people are not directly diagnosed with lung function problems during hospital examinations. Most of them start with shadows and dark shadows, and then further tests. If you are told by the doctor that you have ground-glass opacities in the lungs during the hospital examination, you need to have relevant knowledge and understanding in this regard.

Ground-glass opacities in the lungs, small lung nodules, and lung cancer are three different concepts, and there is no necessary connection between the three.

The conceptual difference between shadow and nodule is that shadow refers to the shadow found in imaging examination, with no limit on size or shape, while nodule refers to a round lesion with clear boundaries within 3 cm. The imaging manifestation of early lung cancer is small lung nodules, but small lung nodules are not equal to lung cancer.

In clinical practice, small lung nodules usually refer to round lesions with a diameter of ≤2 cm found in imaging examinations (X-ray or CT). Those ≤3 cm are called nodules, and those >3 cm are called masses. Some scholars also believe that it is meaningless to divide the nodules too finely. For example, there is no essential difference between a 2.2 cm nodule and a 1.9 cm nodule clinically. For the sake of convenience, nodules ≤3 cm are collectively referred to as small pulmonary nodules, and their characteristics are described uniformly. Among small lung nodules, 60%~70% are benign nodules, and 30%~40% are malignant nodules. Therefore, do not panic if you find small lung nodules.

What are the characteristics of small lung nodules?

On thin-section CT, tumors are divided into three types according to their density. One is a pure ground glass nodule, which appears like frosted glass in the imaging. The postoperative pathology of a pure ground glass nodule is often carcinoma in situ or atypical hyperplasia. Second, some solid ground-glass nodules are often invasive cancers with a higher degree of malignancy. The third is a pure solid nodule, which is a lesion with a higher density and a relatively low probability of malignancy, but once it is malignant, it grows rapidly.

There are also rules to follow in distinguishing the nature of small lung nodules. Generally, round lesions with smooth shape, uniform density, and no lobulation and burrs are mostly benign, while those with irregular shape and burrs are mostly malignant. Clinicians can usually give a clear diagnosis or advice based on the results of imaging examinations, so we don't have to worry about the presence or absence of small lung nodules.

Benign and malignant have their own characteristics

From a pathological point of view, the benign and malignant nature of small lung nodules are different, and the causes of their formation are also different. Benign pulmonary nodules include hamartomas, sclerosing hemangiomas, granulomatous lesions, organizing pneumonia, special infections, and atypical adenomatous hyperplasia (AAH). Malignant lung nodules include adenocarcinoma in situ (AIS), which has no invasion of surrounding tissue stroma; minimally invasive adenocarcinoma (MIA), which has an invasion of surrounding tissue stroma ≤ 5 mm; invasive adenocarcinoma (IA), which has invasion of surrounding tissue stroma and is prone to metastasis; there are also small cell lung cancer, squamous cell carcinoma, large cell lung cancer, carcinoid, etc.

Clinically, some small lung nodules will cause specific symptoms.

Lung inflammation and hemoptysis: There are usually corresponding symptoms such as fever, cough, and hemoptysis.

Post-inflammatory fibrosis: no symptoms or previous history of significant inflammation or bleeding.