Imaging for Sarcoidosis
Sarcoidosis is a systemic disease characterized by widespread development of noncaseating epithelioid granulomas. Based on a joint statement by the American Thoracic Society (ATS), European Thoracic Society (ERS), and the World Association for Sarcoidosis and other Granulomatous Disorders (WASOG), the diagnosis of sarcoidosis requires a compatible clinical picture, histologic demonstration of noncaseating granulomas, and exclusion of other diseases that may give a similar histologic or clinical picture. Although to a casual reader these recommendations suggest that making a diagnosis of sarcoidosis is straightforward, a consensus on the diagnostic role of imaging in sarcoidosis remains unclear. First, despite the primacy of chest computed tomography (CT) for evaluating diffuse lung disease, a guideline-based diagnosis of sarcoidosis without biopsy requires specific appearances on chest radiography (Löfgren's syndrome) or67 Ga Scintigraphy (Heerfordt's syndrome). Second, although the literature on CT as a prognostic tool in interstitial lung disease is relatively extensive, very little of this focuses specifically on sarcoidosis. Third, staging of sarcoidosis relies on radiographic appearances at presentation using a system devised by Scadding more than 40 years ago. This is in stark contrast to idiopathic pulmonary fibrosis where significant advances have been made in imaging-based staging and computer-assisted quantification of disease in the past 10 years. In this article, in addition to describing the myriad of imaging patterns seen in sarcoidosis, the impact imaging has on diagnosis, staging, and prediction of outcome will also be discussed. Cardiac-related sarcoidosis and neurosarcoidosis will be discussed in separate articles.