Contrast-Enhanced Sonography of the Lung for Differential Diagnosis of Atelectasis

OBJECTIVE: Because of the absence of air in atelectatic tissue, sonography allows visualization of lung atelectasis and may characterize pulmonary and bronchial arterial vascularity by contrast-enhanced sonography (CES). METHODS: Thirty consecutive patients with obstructive atelectasis (OA) (n = 17) and compression atelectasis (n = 13) were retrospectively studied by CES using a second-generation sulfur hexafluoride contrast agent (SonoVue [BR1]; Bracco SpA, Milan, Italy). The following CES parameters were evaluated: (1) time to enhancement (TE) of the contrast agent after intravenous application was determined and classified as short TE and delayed TE (short TE, < or =6 seconds; versus delayed TE, >7 seconds); and (2) extent of enhancement (EE) was evaluated during the arterial phase (2-30 seconds) and the parenchymal phase (1-5 minutes): the EE of pleural lesions was determined in comparison with splenic enhancement and classified in reduced EE versus marked EE. RESULTS: All 13 patients with compression atelectasis had a short TE and a marked EE during arterial and parenchymal phases. In the remaining 17 patients with OA, 10 patients had a short TE and 7 patients had a delayed TE. The EE during both phases was reduced in 5 patients and marked in 3. Nine of 17 patients with OA had different EE during arterial and parenchymal phases. CONCLUSIONS: Compression atelectasis is characterized by CES with a short TE and a marked EE, indicating patent pulmonary arterial vascularization. In patients with OA, a variable CES pattern is found. With regard to only the TE, a delayed TE implies OA. This indicates a shifting of pulmonary vascularization to bronchial arterial vascularization in these patients.