Abstract: Objective To analyze the characteristics of atypical high resolution computered tomography (HRCT) findings in patients with pulmonary tuberculosis (TB), and to improve the diagnostic accuracy. Methods A retrospective investigation was conducted. The imaging characteristics of 33 pulmonary TB patients with atypical HRCT findings were analyzed and compared with the HRCT imagings of 50 patients with peripheral lung cancer, 33 patients with invasive lung cancer and 62 patients with nonspecific inflammation (including 33 patients with spherical pneumonia and 29 patients with patchy shadow) respectively. Pulmonary TB cases and non-TB cases (i.e. control group) were divided into 2 sub-groups respectively according to the form of lesions, and then the characteristics of CT imaging of the patients in different groups were compared. A Chi-square test was used to analyze the difference of imaging characteristic between different groups, P<0.01 was regarded as statistically significant.  Results Among 33 TB cases with atypical CT findings, one of the sub-groups (Group 1) contained 15 cases who were confirmed to have tuberculoma. Of which, the CT findings in 9 cases (60.0%, 9/15) showed one or more small, patchy and low-density areas in the lesions and boundaries were vague; the contrast-enhanced CT scanning showed that uneven enhancement appeared in most of patients with tuberculoma (66.7%, 10/15) while even enhancement appeared in most of patients with spherical pneumonia (75.8%, 25/33) and patients with peripheral lung cancer (66.0%, 33/50). The added value range of CT in 10 cases with tuberculoma was between 16-20 HU while the added value was more than 21 HU in 31 cases with spherical pneumonia and 42 cases with peripheral lung can-cer. The added value of CT in patients with tuberculoma was significantly lower than those in spherical pneumonia patients (χ²=20.202, P<0.01) and peripheral lung cancer patients (χ²=20.872, P<0.01). In the other sub-group (Group 2), which contained 18 TB cases whose CT findings showed uniform lesions, more or less slightly lower density areas were seen in lesions of only 2 cases (11.1%, 2/18). The CT findings in TB cases were no significant difference with the findings in patients with spherical pneumonia (2/29) and peripheral lung cancer (0/33); among 12 pulmonary TB cases who received the contrast-enhanced CT scanning, 10 cases (83.3%) showed uneven enhancement with more or less small, patchy and low-density areas in lesions and boundaries were vague while the small and patchy necrosis with vague boundary appeared in only 2 cases (10.5%, 2/19) with pneumonia, and no necrotic area appeared in patients with lung cancer. The features of contrast-enhanced CT scanning in patients with TB and patients with pneumonia, patients with lung cancer were significantly different (χ²=16.433 and 27.692, both P<0.001).  Conclusion Atypical CT findings of pulmonary TB are various, some characteristics of the CT findings may have certain of value for diagnosis, such as patchy opacities and spherical lesions, uneven density and moderate enhancement. For the patients who are difficult to be confirmed diagnosis by CT, their clinical manifestations should be considered and biopsy may be needed too.

Key words: Tuberculosis, pulmonary/radiography, Tomography, X-ray computed