 Introduction/Background Although the true prevalence of mediastinal masses is not known, a 0.9% prevalence of anterior or prevascular mediastinal masses was found among the 2,571 chest CTs of the 51% female cohort of the Framingham Heart Study, with a mean age of 59 years [1]. A 0.73% prevalence of prevascular mediastinal nodules was found on the chest CTs of a 63% male cohort (n = 56,358 participants), with a mean age of 52 years undergoing baseline low- dose chest CT for routine health surveillance [2]. A higher 4% prevalence of mediastinal masses was found on 589 CT pulmonary angiograms in a 63% female cohort with a mean age of 53 years [3]. On baseline lung cancer screening in the Early Lung Cancer Action Project, a 0.77% mediastinal mass prevalence was found in a cohort of 9,263 patients that was 51% female and had a median age of 65 years [4]. The classic imaging approach to mediastinal mass evaluation found on radiography has generally entailed a step- wise progression from chest radiography to CT [12-15] to diagnostic intervention when needed [16,17], with or without an intervening PET/CT. However, more recent recognition of the long-literature-supported ability of MRI to characterize tissue and add diagnostic specificity [18-23], prevent unnecessary biopsy and surgery [24-26], and modify and guide the approach to biopsy and surgery [27] has moved MRI into a valued position in terms of workup and triage of these lesions [28-33]. The American College of Radiology seeks and encourages collaboration with other organizations on the development of the ACR Appropriateness Criteria through representation of such organizations on expert panels. Participation on the expert panel does not necessarily imply endorsement of the final document by individual contributors or their respective organization. Reprint requests to: publications@acr.org Imaging of Mediastinal Masses OR Discussion of Procedures by Variant Variant 1: Clinically suspected mediastinal mass. Initial imaging.
Imaging of Mediastinal Masses.  Introduction/Background Although the true prevalence of mediastinal masses is not known, a 0.9% prevalence of anterior or prevascular mediastinal masses was found among the 2,571 chest CTs of the 51% female cohort of the Framingham Heart Study, with a mean age of 59 years [1]. A 0.73% prevalence of prevascular mediastinal nodules was found on the chest CTs of a 63% male cohort (n = 56,358 participants), with a mean age of 52 years undergoing baseline low- dose chest CT for routine health surveillance [2]. A higher 4% prevalence of mediastinal masses was found on 589 CT pulmonary angiograms in a 63% female cohort with a mean age of 53 years [3]. On baseline lung cancer screening in the Early Lung Cancer Action Project, a 0.77% mediastinal mass prevalence was found in a cohort of 9,263 patients that was 51% female and had a median age of 65 years [4]. The classic imaging approach to mediastinal mass evaluation found on radiography has generally entailed a step- wise progression from chest radiography to CT [12-15] to diagnostic intervention when needed [16,17], with or without an intervening PET/CT. However, more recent recognition of the long-literature-supported ability of MRI to characterize tissue and add diagnostic specificity [18-23], prevent unnecessary biopsy and surgery [24-26], and modify and guide the approach to biopsy and surgery [27] has moved MRI into a valued position in terms of workup and triage of these lesions [28-33]. The American College of Radiology seeks and encourages collaboration with other organizations on the development of the ACR Appropriateness Criteria through representation of such organizations on expert panels. Participation on the expert panel does not necessarily imply endorsement of the final document by individual contributors or their respective organization. Reprint requests to: publications@acr.org Imaging of Mediastinal Masses OR Discussion of Procedures by Variant Variant 1: Clinically suspected mediastinal mass. Initial imaging.