Incidental findings from lung CT scans: implications for research

We aimed to evaluate the number and nature of incidental findings in CT chest scans in the context of a study of the pulmonary effects of cannabis.

Three hundred fifty-seven participants were recruited: 78 cannabis-only smokers, 92 tobacco-only smokers, 106 smokers of cannabis and tobacco and 81 never smokers. All participants underwent a high-resolution CT scan of their thorax. Two radiologists read the scans. Associations between abnormalities and age, sex, tobacco and cannabis smoking status were expressed as odds ratios (OR) with 95% confidence interval.

Seventy-six findings requiring referral or further investigations were found in 71/357 (19.9%) of participants. In multivariate analyses, only older age, OR (per decade) 2.1 (1.4 to 3.0), was associated with a respiratory abnormality on the CT scan. A total of 37/76 (48.7%) of the abnormalities detected were extra-pulmonary, with findings observed across a wide range of organ systems. Only older age, OR (per decade) 1.7 (1.2 to 2.5), was associated with a non-respiratory abnormality.

The common occurrence of abnormal findings requiring referral or further investigations raises practical, ethical and medico-legal issues which need to be carefully considered in research programmes utilising chest CT scanning.