Relationship between CT findings of pulmonary tuberculosis and the number of acid-fast bacilli on sputum smears

Purpose: To investigate the relationship between computed tomography (CT) findings in patients with active pulmonary tuberculosis (PTB) and the number of acid-fast bacilli (AFB) on sputum smears. Methods: We reviewed CT scans of 173 patients with active PTB. The patients were divided into groups according to the number of AFB on sputum smears as follows: A, negative (n=40); B, doubtful (n=21); C, + (n=34); and D, ++ or greater (n=78). The presence or absence and the number of lobes that included micronodules, nodules, consolidation and cavitation, the number of cavities and the maximum diameter of the cavity lumen were noted. Results: The frequency of micronodules and nodules did not significantly differ among the four groups. In contrast, the frequency of consolidation and cavitation increased with the number of AFB (P<.0001). Differences in the number of lobes involving micronodules, nodules, consolidation and cavitation were significant between Group D and the other groups (P<.0001), but not between Groups A or B and C. The number and maximum size of cavities significantly differed between Group D and the other groups (P<.0001). Conclusions: CT findings correlated with the number of AFB in sputum smears to some extent. However, CT findings do not reliably discriminate between smear-negative patients and those with very few AFB excreting smear-positive patients.