Need Entire Chest on Cardiac CT to Detect Lung Cancer Lung Cancer Detected at Cardiac CT: Prevalence, Clinicoradiologic Features, and Importance of Full-Field-of-View

Background: Cardiac CT imaging is gaining in popularity. When imaging the heart with CT, additional structures are visualized, including the lungs. Whether the lung fields should be evaluated during cardiac CT imaging is controversial. Some cardiology groups believe that analyzing the lung fields will only lead to increased patient anxiety and increased costs without clinical benefit. Objective: To determine the prevalence of lung cancer detected at cardiac CT imaging and to compare the detection rates at different field-of-view (FOV) settings. Design: Retrospective review. Participants: Patients referred to cardiac CT imaging for clinical reasons. Patients with known lung cancer were excluded. Methods: Patients underwent either 16-slice or 64-slice cardiac CT imaging with IV contrast. Images were reconstructed 2 different ways. The first was a limited FOV reconstruction that included the heart and 1 to 4 cm from the farthest anterior, posterior, and lateral extents of the cardiac chambers. The full FOV reconstructions included the entire lung parenchyma contained within the imaged portion of the thorax. After the initial cardiac scan, delayed images were obtained, which included the entire thorax and complete lung fields. No additional contrast was given for these delayed images. Patient exposure was estimated to be 8 mSv for cardiac imaging and 7 mSv for the delayed thoracic imaging. Results: In the group evaluated, the mean patient age was 58 years, and 58% of patients were male. The clinical reasons for cardiac CT angiography were screening for coronary artery disease (CAD) in asymptomatic patients (51%); suspected CAD (42%); known CAD (6%); and other cardiac disease (1%). Unsuspected lung cancer was discovered in 36 patients (prevalence, 0.31%). Of these cancers, about two-thirds were in a resectable stage (23 of 36 were stage IIIA or less). Limited FOV reconstructions detected 4 cancers (11%), full FOV reconstructions (cardiac) detected 19 (53%), and full FOV reconstructions (thoracic) detected all 36 cancers (100%). Limited FOV reconstructions missed 32 of the 36 cancers detected by full FOV reconstructions (thoracic). Conclusions: The prevalence of unsuspected lung cancer in patients undergoing cardiac CT angiography was 0.31%. If only limited FOV reconstructions are evaluated, then approximately 90% of these cancers would be missed. Reviewer's Comments: The authors recommend that, at the very least, the entire scan be evaluated when performing cardiac CT angiography. The argument that the additional knowledge obtained by evaluating the entire scan will only lead to patient anxiety and useless additional testing simply suggests that physicians need to know how to read the scans better and respond to the information contained in a manner that does not increase patient anxiety or lead to useless tests. (Reviewer-Thomas F. Heston, MD).