Computed tomographic scanning in sarcoidosis.

Sarcoidosis is a granulomatous disease of unknown etiology that involves the lungs or intrathoracic lymph nodes in more than 90% of patients. The clinical spectrum of sarcoidosis is protean, but pulmonary manifestations often dominate. Chest radiographs are abnormal in 90 to 95% of patients with sarcoidosis; the most characteristic feature is bilateral hilar lymphadenopathy (BHL), present in 50 to 80% of patients. Pulmonary parenchymal infiltrates are present in 25 to 50% of patients. In this article, we review the radiographic features of sarcoidosis (both typical and atypical), and the impact of chest radiographic stage on long-term prognosis. Computed tomographic (CT) scans are more sensitive than chest radiographs in delineating parenchymal, mediastinal, and hilar structures, and distinctive CT patterns may be virtually pathognomonic for sarcoidosis in some patients. Routine CT scan is not appropriate to diagnose or manage sarcoidosis, but CT may be invaluable in patients with atypical clinical or chest radiographic findings or specific complications of sarcoidosis (pulmonary or extrapulmonary), or to assess prognosis. High-resolution thin-section CT scans (HRCT) may be helpful in selected patients with stage II or III sarcoidosis to discriminate active inflammation from irreversible fibrosis. This article discusses the salient HRCT features of sarcoidosis, accuracy of CT in the differential diagnosis, and correlations of HRCT with disease extent and activity, pulmonary function, and lesion reversibility.