ObjectiveTo investigate the relationship between primary pulmonary mucinous adenocarcinoma (PPMA) mass type and pneumonia type and the difference of 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 relationship between Ki-67 index and the degree of malignancy between the two groups were analyzed and compared, and the diagnostic ability of PPMA was enhanced. 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 statistically significant differences between the two groups in the maximum diameter of tumor, boundary condition and pleural indentation sign (P<0.05). There was no significant difference between the two groups in Ki-67% index and its high and low value-added groups (P>0.05). ConclusionThere is no significant difference in the degree of malignancy between the two types of PPMA, which supports that the pneumonia type is only the manifestation of the disease progression of the lump type. PPMA is more common in elderly women and often occurs in both lower lungs. The clinical manifestations are mainly cough and white mucinous sputum. CT scans can show various manifestations, among which the reversed hato-like sign is expected to become an important imaging feature. Combined with high solid fraction, pleural indentation sign, and vacuole sign, it can play a significant auxiliary role in its diagnosis.