Fluid in space between the lung and the chest wall is termed a pleural effusion . There needs to be at least 75ml of pleural fluid in order to blunt the costophrenic angle on the lateral chest radiograph, and 200ml on the posteroanterior chest radiograph. On a lateral decubitus, amounts as small as 50ml of fluid are possible. Pleural effusions typically have a meniscus visible on an erect chest radiograph, but loculated effusions (as occur with an empyema ) may have a lenticular shape (the fluid making an obtuse angle with the chest wall).
Chest pain is a common presenting problem . Overall chest pain is responsible for an estimated 6% of all emergency department in the United States and is the most common reason for hospital admission.  Chest pain is also very prevalent in primary care clinics , representing 1-3% of all visits with primary care physicians.  The rate of emergency department visits in the US for chest pain decreased 10% from 1999 to 2008.  but a subsequent increase of 13% was seen from 2006-2011.  Less than 20% of all cases of chest pain admissions are found to be due to coronary artery disease.  The rate of chest pain as a symptom of acute coronary syndrome varies among populations based upon age, sex, and previous medical conditions .  In general, women are more likely than men to present without chest pain (49% vs. 38%) in cases of myocardial infarction.