Final answer:
A patient with a collection of pus in the pleural space has a purulent pleural effusion or empyema, often caused by infection and diagnosed with imaging such as a chest radiograph and further guided by Gram staining for appropriate treatment.
Step-by-step explanation:
A patient who has a collection of pus in the pleural space has a condition known as pleural effusion that is specifically purulent, also termed empyema. This accumulation occurs when the pleural membranes, which line the lungs and the chest cavity, become infected. The pus is an accumulation of dead pathogens, neutrophils, tissue fluid, and other cells that have been cleared by the body's immune response during an infection. A chest radiograph typically helps in diagnosing this condition, often showing fluid in the space between the pleural membranes. Moreover, a Gram stain can aid in identifying the type of bacteria causing the infection, which is critical for guiding appropriate antibiotic therapy.