Pulmonary nodular shadow generally refers to the abnormal density shadow found through lung imaging, the abnormal density shadow is called pulmonary nodular shadow if its diameter length is less than 3cm, and pulmonary mass if it is larger than 3cm. The presence of pulmonary nodular shadow often indicates the occurrence or occurrence of lesions in the lung, and whether it is serious or not depends on the volume and density of pulmonary nodular shadow. There are three classifications of pulmonary nodule shadow according to diameter. A pulmonary nodule shadow with a diameter of less than 5 mm is a microscopic nodule, a small nodule with a diameter of 5-10 mm, and a pulmonary nodule with a diameter of less than 30 mm. Small nodules and pulmonary nodules often indicate benign lesions, which are generally not serious and can be treated with regular observation, while small nodules and pulmonary nodules often indicate the possibility of malignant lesions, such as adenocarcinoma of the lung, small cell carcinoma or tuberculosis, which are relatively more serious and require other tests, such as enhanced CT and pathological examination, for further diagnosis and symptomatic treatment. According to the density of the lung nodule shadow, there are solid lung nodules, ground glass lung nodules and partially solid lung nodules. Solid pulmonary nodules are often more serious because they generally indicate more malignant diseases, such as lung cancer and pulmonary embolism, and other related tests are needed to confirm the diagnosis and manage accordingly. Glassy nodules and some solid nodules are low to moderate risk nodules, which often indicate less serious lesions such as pneumonia and pulmonary calcification foci, and can be treated with medication or reviewed regularly. The severity of pulmonary nodules is affected by many factors, and the diagnosis of pulmonary nodules requires a combination of various tests, such as imaging, laboratory tests, and pathology, and cannot be confirmed by imaging results alone.