A 41-year-old man is admitted with severe shoness of breath. He complains of a 25-lb weight loss over the last 2 mo and occasional vomiting after meals. On physical examination, vital signs are: pulse 110 bpm; temperature 98degF; respirations 24/min; blood pressure 110/70 mm Hg. Peinent findings: dullness to percussion on the left posterior chest with decreased breath sounds. A patchy area of egophony is heard over the left upper lung field posteriorly. PPD is 15 mm. CXR is shown in. The most likely diagnosis is

The x-ray shows a homogenous shadow of the left chest with an area of hyperlucency representing normal lung surrounded by fluid. The lateral curved shadow is called the "meniscus sign" and is indicative of pleural fluid tracking up the side of the lung. The mediastinum is pushed into the contralateral chest. This patient complained of shoness of breath with physical signs of a left-sided pleural effusion. This is confirmed by the chest x-ray. The clinical presentation in this afebrile patient without any airspace disease makes community-acquired pneumonia unlikely. Atelectasis of theleft lung due to mucus plugging or aspiration would produce a homogenous opacity with ipsilateral shift of the mediastinum. In this case the meniscus sign and the contralateral mediastinal shift make the diagnosis of pleural effusion very likely.