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A, B. A 37-year-old man with bloody sputum since > 3 months. Chest CT reveals an ovoid opacity located within a lung cavity. C, D. A 59-year old man with cough and bloody sputum. Chest CT reveals a round, high-density, soft-tissue lesion (diameter, 4.2 cm) in the right, upper lung. A curved air shadow, i.e., the air crescent sign, is seen within the lesion. In the mediastinal window, subtraction is not obvious.
