A pulmonary nodule of 2 cm specifically refers to its diameter of 2 cm and has a benign chance of being more than 90%. Because larger pulmonary nodules are mainly more than 3cm in diameter, most of the pulmonary nodules below this figure are benign lesions. For example, pulmonary tuberculosis caused by infection with Mycobacterium tuberculosis, inflammatory pseudotumor due to bacterial pneumonia caused by bacteria such as Staphylococcus aureus, Klebsiella, and Pseudomonas aeruginosa, resulting in small nodules that can be cured by anti-inflammatory treatment. In addition, they are also seen in teratomas and malignant nodules of less than 3 mm in diameter, and only a very small number of them, about 10%, or even a smaller number, are seen in malignant nodules, such as bronchial lung cancer, and the clinical diagnosis is confirmed by taking the nodules from the lungs for biopsy.