Pulmonary pseudonodules on computed tomography: a common pitfall caused by degenerative arthritis

This study assessed the prevalence of pseudonodules of the lung on computed tomography (CT) related to degenerative arthritis at the distal first rib and sternum. A total of 250 serial chest CT scans were retrospectively reviewed by a chest and a musculoskeletal radiologist. A pseudonodule was defined as a round or oval opacity identified on lung window surrounded by aerated lung and superimposable on an osseous structure on the immediate cephalad slice. The pseudonodules were classified as originating from one of the following three locations: first costochondral junction, first costosternal junction, or sternoclavicular junction. CT slice thickness was 8 mm or 10 mm. For each side, the presence of a pseudonodule and its classification was noted. The presence or absence of degenerative arthritis was also noted for each side. The median patient age of the 111 men and 139 women was 62 years (range, 2-97). Degenerative arthritis was noted bilaterally in 94 (38%) and unilaterally in two. Pseudonodules were present in 29 patients (12%). Eighteen (62%) were men with a median age of 73 years (range, 50-84), and 11 (38%) were women with a median age of 67 years (range, 52-85). All of the patients with pseudonodules had bilateral degenerative arthritis. Twenty-seven pseudonodules were caused by degenerative arthritis at the first costochondral junction, four at the first costosternal junction, and one at the sternoclavicular junction. Fifteen pseudonodules were right sided and 17 were left sided. Three patients had bilateral pseudonodules. Pulmonary pseudonodules caused by degenerative arthritis, most commonly at the first costochondral junction, were present in 12% of our series. This common finding occasionally may be misinterpreted as a true pulmonary nodule.