Imaging aspects of the diagnosis of sarcoidosis.

UNLABELLED: Sarcoidosis is a systemic granulomatous disorder of unknown aetiology with a wide spectrum of radiological appearances and almost invariably pulmonary involvement. Lung involvement accounts for most of the morbidity and much of the mortality associated with sarcoidosis. Imaging contributes significantly to the diagnosis and management of patients with sarcoidosis. In typical cases, chest radiography may be sufficient to establish the diagnosis with little margin of error and CT is not necessary. However, CT can play a critical role in several clinical settings: atypical clinical and/or radiographic findings; normal or near-normal chest radiograph but clinical suspicion of sarcoidosis; and detection of complications. Moreover, in many patients, CT findings are atypical and unfamiliar to most radiologists (e.g. sarcoidosis mimicking other lung diseases and vice versa), and in these cases histological confirmation of the diagnosis is recommended. CT is also useful in assessing disease extent and may help to discriminate between reversible and irreversible lung disease, thus providing critical prognostic information. This review concentrates on the more difficult imaging aspects of sarcoidosis, in particular differential diagnosis and disease complications. KEY POINTS: •Sarcoidosis is characterized by a wide spectrum of radiological appearances. •In typical cases, imaging substantially contributes to the diagnosis of sarcoidosis. •CT plays a critical role in atypical and complicated cases. •CT may discriminate between reversible and irreversible lung disease.