Computed tomography in secondary spontaneous pneumothorax: Reading the fine print

Objectives: To identify specific characteristics, distribution and associated findings of lesions causing secondary spontaneous pneumothorax (SSP). Methods: Computed tomography (CT) chest of 37 patients (between October 2011 and January 2020) was evaluated by two radiologists. They were classified into 'Infectious' and 'Non-infectious' groups, based on cause of pneumothorax. A scoring system (score 0-10) was proposed based on parameters which were statistically significant. Results: Out of 37 patients with pneumothorax, 18 could be attributed to infectious aetiology and remaining 19 were due to noninfectious causes. The most common infectious cause of spontaneous pneumothorax was tuberculosis and noninfectious cause was chronic obstructive airway disease (COAD). Statistically significant difference was found for lesion wall thickness and presence of solid component between these two groups. No significant difference was found between both groups when comparing age, gender, lesion size and lesion distribution. The presence of pleural thickening, consolidation and mediastinal lymphadenopathy were statistically significant. Pleural effusion was never present in the noninfectious group. The area under receiver operating characteristic for differentiating patients in the two groups was 0.931 (standard error, 0.038; 95% CI, 0.856-1.000), and optimal threshold score for identifying patients with infectious causes was 4.5, with 77.8% sensitivity and 89.5% specificity. Conclusion: Pneumothorax is almost equally common due to infectious and noninfectious causes. The most common infectious cause of spontaneous pneumothorax was tuberculosis and noninfectious cause was COAD. Based on certain CT findings, we have proposed a scoring system to differentiate between these two groups.