Radiological and nuclear medicine imaging of sarcoidosis

Sarcoidosis is a multisystem chronic inflammatory disease of unknown etiology characterized by widespread growth of non-caseating granulomas. The diagnosis of sarcoidosis is based on clinical and imaging presentation, histologic confirmation and the absence of alternative diseases. Radiology and Nuclear Medicine play an essential role in the diagnostic work-up of patients with sarcoidosis to assess disease extent and activity. In addition, imaging modalities have shown their potential in managing these patients in terms of treatment response and prognostic assessment. Sarcoidosis has a predilection for chest involvement, showing typical and atypical manifestations in the lungs, airways and hilar/mediastinal lymph nodes. Chest radiography (X-ray) still plays an important role in suggesting diagnosis for cases with typical presentation of sarcoidosis, while computed tomography (CT) has higher accuracy in detecting early stage disease and in narrowing differential diagnosis, particularly in atypical manifestations. For extrathoracic involvement, both CT and MR (magnetic resonance) have comparable performance even though MR is the modality of choice for assessing neurosarcoidosis and cardiac sarcoidosis. In the last decades positron emission tomography/CT (PET/CT) has demonstrated an increasing and relevant value in assessing disease extent and activity, treatment planning and therapy response, with a crucial role in the management of cardiac sarcoidosis. In this article, an overview of the possible imaging manifestations of thoracic and extrathoracic sarcoidosis and current concepts on staging, response assessment and prognosis is provided. Finally, the potential applications of non-FDG radiotracers is briefly discussed.