The air crescent sign: A clue to the etiology of chronic necrotizing pneumonia.

A 44-year-old man with a history of emphysema presented with 2 days of blood-tinged sputum. Prior to this, he had noticed fever with night sweats, generalized weakness, weight loss, and cough for 2 months. He is a known alcoholic who appeared chronically ill, poorly nourished, and emaciated. He was febrile, and lung auscultation revealed rales over the right upper chest. The blood leukocyte count was 20,000/ L with 87% polymorphs. His blood tested negative for HIV infection, and the skin test result with purified protein derivative was negative. Chest radiography (Fig 1) revealed patchy airspace disease with areas of lucency suggestive of cavitation in the right upper lobe, and emphysematous changes bilaterally. A CT scan of the chest (Fig 2) revealed a crescent-shaped lucency (air crescent sign) within the area of consolidation in the right upper lobe. Multiple sputum smears revealed no bacteria and no acid-fast bacilli. Sputum cultures revealed no bacterial growth. The patient underwent fiberoptic bronchoscopy that revealed only purulent secretions in the right upper lobe bronchus without any endobronchial lesions. Lavage smears revealed no bacteria or acid-fast bacilli. Four weeks of treatment for tuberculosis resulted in no clinical or radiographic improvement.