ObjectiveTo investigate the relationship between primary pulmonary mucinous adenocarcinoma (PPMA) mass type and pneumonia type and their difference in malignant degree, and to analyze the role of clinical manifestations and CT features in the diagnosis of this disease. MethodsThe clinical data of PPMA patients admitted in the First Affiliated Hospital of Xiamen University from May 2011 to March 2022 were retrospectively analyzed. According to CT features, they were divided into a mass type group and a pneumonia type group. The clinical manifestations, CT features and the degree of malignancy between the two groups were analyzed and compared. ResultsA total of 57 PPMA patients were enrolled. There were 17 males and 40 females, with an average age of (53.82±10.65) years, and 28 (49%) patients had reversed hato-like sign. There were 42 patients in the mass type group and 15 patients in the pneumonia type group. PPMA often occurs in both lower lungs, with clinical manifestations mainly of coughing and expectorating white mucoid sputum. There were statistical differences between the two groups in the maximum diameter of tumor (P<0.001), boundary condition (P<0.001) and pleural indentation sign (P=0.019). There was no statistical difference between the two groups in Ki-67 index (P>0.05). ConclusionThere is no statistical difference in the degree of malignancy between the two types of PPMA. Considering their clinical manifestations and differences in imaging features, it is supported that the pneumonia type is just a progression of the mass type. CT can present various manifestations, among which the reversed hato-like sign is expected to become an important imaging feature. Combined with a high proportion of solid components, pleural indentation sign, and vacuole sign, reversed hato-like sign can play a significant role in the diagnosis of PPMA.