Differential diagnosis of intrapulmonary nodules: the main issue is the differentiation of peripheral lung cancer, inflammatory nodules and tuberculosis bulbs; most benign tumors are round-like nodules without lobulation or with superficial lobulation, and generally do not have signs such as burrs, spicules, pleural depressions, satellite lesions and pulmonary vascular encapsulation aggregates. 1. Popcorn-like calcification within the nodule should be considered as a misshapen tumor. Lipomas have specific density values, and other benign tumors show no specificity. Single metastases in the lung are difficult to distinguish from most benign nodules from imaging. Signs that have greater differential value for peripheral lung cancer, inflammatory nodules and tuberculosis spheres are nodule morphology, lobar sign, multicystic translucent shadow, pleural depression sign, burr sign and calcification. Clear nodule margins are important to support the diagnosis of lung cancer nodules. Adjacent pleural thickening and satellite lesions help to exclude lung cancer nodules. Spicules are difficult to grasp, and pulmonary vascular aggregates are of little significance for differentiation because of the similar percentage and frequency of appearance in the 3 types of lesions. 2. Studies have shown that nodule morphology and degree of lobulation are the most valuable signs for differentiation, which is consistent with some scholars who advocate that analysis based on lesion morphology combined with internal margins of the lesion adjacent to lung tissue and pleural signs is the basic method to correctly diagnose intrapulmonary nodules. Typical deep lobar nodules reflect the aggressive biological behavior of tumor and the growth pattern of cell accumulation, which are the most fundamental signs of peripheral lung cancer, while inflammatory nodules are mostly atypical nodules, i.e., wedge-shaped, elongated, polygonal or lamellar shadows on the imaging, which are closely related to the pathological process of inflammatory lesion development. The “square sign” proposed by Zulong Cai et al. and the “centripetal square depression sign” and “edge pinch sign” proposed by Yunfeng Cui et al. are of great value for the diagnosis of nodules. Inflammatory pseudotumor is a chronic granuloma transformed by non-absorption of inflammatory lesions, mostly with envelope, occasionally with deep lobulation, and with clear borders, which is difficult to distinguish from lung cancer nodules. The finding of nodule margins such as satellite lesions and pleural thickening should be more inclined to inflammatory pseudotumor. Tuberculosis spheres are foci of caseous necrosis surrounded by fibrous tissue, which are still chronic granulomas in nature. Since tuberculosis spheres do not have the biological behavior and growth pattern of tumors, most of them are typical nodules without lobulation or with only superficial lobulation. After determining the morphology and degree of lobulation, clear margins of lesions, burr sign, spiny protrusions and pleural indentation sign all help to diagnose lung cancer. Multicystic translucent shadow is not present at a high rate, but strongly suggests lung cancer; satellite lesions, pleural thickening and calcification have some value to exclude lung cancer, especially bronchial dilatation around the lesions is important to exclude lung cancer nodules. Calcifications should be analyzed in terms of quantity, distribution and morphology. Large amount, central, concentric circles or popcorn-like calcifications are mostly suggestive of benign, while scattered, punctiform or amorphous calcifications tend to be malignant. Satellite lesions such as blurred margins, peripheral bronchial dilatation and pleural thickening are consistent with perifocal exudation. 3.Most signs of inflammatory nodules and tuberculosis spheres have similar percentage and frequency, which is consistent with the pathological basis that tuberculosis spheres are a kind of specific granuloma, but tuberculosis spheres preferably occur in the upper lung and grow close to the pleura, and satellite lesions have various morphologies, and calcification is common in nodules, and most of them do not strengthen after enhancement, or show circumferential strengthening, which also has auxiliary diagnostic significance. 4.Local infiltration of early lung cancer cells is a faint shadow with blurred edges. When the tumor is of multicenter origin, the morphology is irregular and resembles multiple nodule accumulation.