To analyze the classification and clinical differential diagnosis of primary lung carcinoid (PLC), to compare the differences between typical and atypical carcinoid imaging signs, and to improve the level of imaging diagnosis of lung carcinoid.

The clinical and CT data of 54 patients with primary pulmonary carcinoid confirmed by histopathology were retrospectively analyzed, including 21 cases of typical carcinoid and 33 cases of atypical carcinoid. The two patients were compared, including location, size, shape, progression, margin, calcification, metastasis, plain scan and enhanced CT values.

The 21 cases of typical carcinoid and 33 cases of atypical carcinoid were divided into central type and peripheral type, 15/6 cases and 4/29 cases respectively (P<0.001). The central type was dominant in typical carcinoid and the peripheral type was dominant in atypical carcinoid. The mean diameter of 21 cases typical carcinoid patients was (1.85±1.10) cm, with nodules in 18 cases and mass in 3 cases. The average diameter of 33 cases atypical carcinoids was (4.36±2.54) cm, 13 cases were nodules, and 20 cases were clumps (P<0.05). Typical carcinoids were mainly nodules, while atypical carcinoids were larger than typical carcinoids and mainly clumped. The margins of typical carcinoid and atypical carcinoid were segmented and smooth, with 13/8 cases of typical carcinoid and 5/28 cases of atypical carcinoid (P<0.001). No metastases were found in typical carcinoids, and 15 cases of atypical carcinoids showed metastases (P<0.001). There was no significant difference in shape and calcification between typical carcinoid and atypical carcinoid (P>0.05). The CT values of plain scan were (37.32±19.26)Hu and (33.74±13.30)Hu, respectively. The average intensification values were (61.38±34.72)Hu and (51.87±27.86)Hu, respectively.

There were some differences in the location, size, shape, margin, calcification, enhancement and metastasis of typical carcinoid and atypical carcinoid, which were statistically significant (P<0.05). Understanding the differences in the above signs would help to distinguish the two carcinoids.