Incidental Lymphadenopathy at CT Lung Cancer Screening.

Abstract

HomeRadiologyVol. 302, No. 3 PreviousNext Reviews and CommentaryFree AccessEditorialIncidental Lymphadenopathy at CT Lung Cancer ScreeningTheresa C. McLoud Theresa C. McLoud Author AffiliationsFrom the Department of Radiology, Massachusetts General Hospital, 55 Fruit St, Boston, MA 02114-2696.Address correspondence to the author (e-mail: [email protected]).Theresa C. McLoud Published Online:Nov 23 2021https://doi.org/10.1148/radiol.212168MoreSectionsPDF ToolsImage ViewerAdd to favoritesCiteTrack CitationsPermissionsReprints ShareShare onFacebookTwitterLinked In See also the article by Chalian et al and the editorial by Mascalchi and Zompatori in this issue.Dr McLoud is a professor of radiology at Harvard Medical School, vice chair for education at the Massachusetts General Hospital Department of Radiology, and a thoracic radiologist. Her research interests have been in lung cancer staging and screening, interstitial lung disease, and educational methodology in radiology.Download as PowerPointOpen in Image Viewer Lung cancer is the most common cause of cancer death in the United States. Most types of lung cancer are curable if detected at an early stage. The National Lung Screening Trial (NLST) convincingly demonstrated that lung cancer screening with low-dose chest CT resulted in a 20% reduction in lung cancer mortality compared with chest radiography (1). The value of lung cancer screening was confirmed in the NELSON trial in Europe (2). Although the methodology was somewhat different and patients were followed for 10 years, the lung cancer mortality for men was reduced in the screened population by 24%. For a smaller group of screened women, there was a 48% reduction in mortality.However, one of the major shortcomings of lung cancer screening with low-dose CT is the large number of incidental findings detected on CT scans (3,4). Most of these are clinically insignificant, but some require attention and can be important to clinical care. The reported prevalence and the associated costs of incidental findings are quite variable. In the NLST and other worldwide clinical trials for lung cancer screening, the rates of clinically significant incidental findings varied, with 1% in the NELSON trial and 19% in a Canadian center trial (5). Included in the American College of Radiology Lung CT Screening Reporting and Data System, or Lung-RADS, is a category “S” modifier for clinically significant or potentially clinically significant nonlung cancer findings that can be added to any of the Lung-RADS categories 0–4 coding for nodules. The American College of Radiology estimates the prevalence of “S” modifiers to be approximately 10%.Many incidental findings among those screened for lung cancer are related to smoking (4). Emphysema is the most common. Cigarette smoking is also associated with higher risks of interstitial lung diseases, particularly idiopathic pulmonary fibrosis. Other incidental findings common in smokers include pulmonary infections and pulmonary or pleural disease associated with asbestos exposure. Cardiovascular disease is also associated with cigarette smoking, and incidental findings at screening chest CT include coronary calcifications and thoracic aortic aneurysms. The list of other frequent incidental findings includes thyroid nodules and extrapulmonary malignancies. The most commonly reported are pancreatic cancers, hepatocellular carcinoma, and renal malignancies.Lymphadenopathy (defined as lymph nodes ≥1 cm in the short axis) can be due to infections, edema, diffuse lung disease such as sarcoidosis, and, less commonly, lymphoma and metastatic carcinoma. The prevalence of incidental enlarged lymph nodes in the setting of lung cancer is reported to be low. In one group of patients screened for lung cancer, mediastinal or hilar adenopathy was present in 1.6% of patients in the absence of pulmonary nodules smaller than 4 mm (6). Other studies have reported even lower rates, ranging from 0.13% to 1.0%. In the Continuous Observation of Smoking Subjects, or COSMOS, study, five cases of lymphoma were detected among 5201 patients (7). However, lymphoma was the second most common nonlung cancer malignancy after renal carcinoma among smokers. It has been suggested that mildly enlarged mediastinal or hilar lymph nodes do not require further diagnostic work-up, especially if other causes besides lung cancer—such as pulmonary edema, fibrosis, infection, or sarcoidosis—are present.In this issue of Radiology, Chalian and colleagues report a well-designed study that establishes the clinical significance of mediastinal lymphadenopathy in individuals undergoing lung cancer screening (8). The data and cases were obtained from the prevalence screening examinations in the NLST. There were only 422 positive scans for lymphadenopathy among over 26 000 CT trial participants (1.6%). The frequency of lung cancer diagnosis and lung cancer stage and histologic findings in the lymphadenopathy group were compared with the control group of over 26 000 NSLT participants, and those with enlarged nodes at the initial CT examination had a higher incidence of lung cancer when compared with NLST participants without lymphadenomegaly (17.1% vs 3.9%; P < .001). The authors found an association between larger mediastinal lymph node size and a higher incidence of lung cancer, a later stage of presentation, increased deaths, and reduced survival times in the NLST participants. The time to a lung cancer diagnosis was also shorter in the lymphadenopathy group, as most cases were diagnosed within the first 3 years, although the majority were within the 1st year. These findings suggest that although lymphadenopathy is usually considered an incidental finding during lung cancer screening, particularly if there is no other compelling evidence of likely lung cancer (ie, a nodule >8 mm in diameter). However, it seems reasonable based on the data provided by these authors that a shorter-term follow-up after the initial screen with low-dose CT would be preferable. As the authors emphasize, there is currently no evident recommendation from the American College of Radiology or other scientific societies regarding the treatment of patients with lymphadenopathy detected at lung cancer screening, particularly in the absence of a suspicious nodule larger than 8 mm or other findings suggestive of lung cancer. In the Lung-RADS guidelines, lymphadenopathy is considered an incidental finding. The authors also suggest further evaluation with PET/CT and a 3-month follow-up. However, false-positive results with PET/CT due to inflammatory conditions are frequent, and 3 months may not be sufficient to demonstrate interval change. A 6-month follow-up might appear more reasonable.The authors have not addressed the possibility of lymphoma as a cause of lymphadenopathy detected during screening. Lymphoma does appear to be rare in patients with lung cancer. Based on the evidence presented, it appears that mediastinal adenopathy detected in lung cancer screening should not be considered an “incidental finding,” and short-term follow-up, preferably at 6 months, should be instituted.Disclosures of conflicts of interest: T.C.M. No relevant relationships.