An empyema is a collection of pus in the pleural space, the thin gap between your lungs and the chest wall. It most often develops as a complication of pneumonia, when bacteria spread from infected lung tissue into the surrounding cavity. Left untreated, the infection progresses through distinct stages, eventually forming a thick rind of scar tissue that can permanently restrict lung function.
How Empyema Develops
Your lungs are surrounded by two thin membranes called the pleura, with a small amount of fluid between them that lets the lungs glide smoothly as you breathe. When a lung infection like pneumonia sends bacteria into this space, the body responds with inflammation. Fluid builds up, white blood cells flood the area, and what starts as a watery effusion gradually thickens into frank pus.
Pneumonia is the most common trigger, but empyema can also follow chest surgery, a chest injury, or the spread of infection from the abdomen. People with weakened immune systems, chronic lung disease, diabetes, or alcohol use disorder face a higher risk. In rare cases, a lung abscess can rupture directly into the pleural space.
The Three Stages
Empyema doesn’t appear all at once. It moves through three recognized stages, each with a different character and level of severity.
Exudative Stage
The earliest phase looks a lot like pneumonia itself. You may have fever, cough, and a sharp chest pain that worsens when you breathe in. Shortness of breath is usually mild, and the chest discomfort often feels like a deep, dull ache. At this point the fluid in the pleural space is still relatively thin and free-flowing, which makes it easier to treat.
Fibrinopurulent Stage
As the infection takes hold, the fluid thickens and fibrous strands form inside it, dividing the collection into pockets (called loculations). Chest pain worsens. You may develop a productive cough with thick, discolored sputum. Fever climbs, and constitutional symptoms like night sweats, fatigue, and general malaise set in. Breathing becomes noticeably harder because the thickening fluid compresses the lung.
Organizing Stage
If the infection isn’t controlled, the body lays down a dense layer of scar tissue (called a “peel” or cortex) over the surface of the lung. This rigid coating traps the lung and prevents it from expanding normally, a condition known as lung entrapment or fibrothorax. Symptoms at this stage are chronic: persistent pain, severe shortness of breath, marked weight loss, and poor exercise tolerance. Reversing the damage at this point typically requires surgery.
Symptoms to Recognize
The symptoms of empyema overlap heavily with pneumonia, which is part of what makes it tricky to catch early. The key difference is that empyema symptoms persist or worsen even when pneumonia treatment is underway. If you’ve been treated for pneumonia but your fever keeps climbing, your breathing deteriorates, or your chest pain shifts from sharp to a deep, constant ache, those are signals that fluid may be accumulating in the pleural space.
Common symptoms across all stages include:
- Fever and chills, sometimes with drenching night sweats
- Chest pain that worsens with breathing or coughing
- Shortness of breath that progressively worsens
- Cough, often producing thick or foul-smelling sputum
- Fatigue and malaise
- Unintentional weight loss in later stages
A rapid heart rate and fast, shallow breathing can indicate the infection is triggering a systemic inflammatory response, which signals a more serious situation.
How It’s Diagnosed
Chest X-rays can show fluid in the pleural space, but a CT scan with contrast gives a much clearer picture. One hallmark finding on CT is called the “split pleura sign,” where both layers of the pleura appear thickened and separated by fluid. This sign is strongly associated with empyema: it has roughly 81% sensitivity and 75% specificity for distinguishing empyema from a simpler, uncomplicated fluid collection. On multivariate analysis, it carries about a 6.7-fold increased likelihood of empyema compared to a plain parapneumonic effusion.
The definitive test, though, is a thoracentesis, where a needle is inserted into the pleural space to withdraw fluid for analysis. Pus visible to the naked eye confirms the diagnosis immediately. Even when the fluid isn’t obviously purulent, lab analysis can reveal the hallmarks: very low pH (below 7.2), low glucose, high levels of cell-breakdown enzymes, and bacteria on culture or stain.
Treatment by Stage
Treatment depends heavily on which stage the empyema has reached. Every case requires antibiotics, typically given intravenously at first and then switched to oral antibiotics for a course that often runs several weeks. But antibiotics alone rarely resolve empyema because they penetrate poorly into thick pus and walled-off fluid collections.
In the exudative stage, draining the fluid with a needle or a small chest tube may be enough, combined with antibiotics. This is the most straightforward scenario, and catching empyema at this point gives the best chance of a full recovery without surgery.
Once loculations form during the fibrinopurulent stage, simple drainage often fails because the pockets of pus can’t all be reached by a single tube. Doctors may instill clot-dissolving and thinning agents directly into the pleural space through the chest tube to break up the fibrous walls and improve drainage. If that approach doesn’t work, surgical intervention becomes necessary.
By the organizing stage, surgery is almost always required. The thick scar tissue encasing the lung must be physically peeled away, a procedure called decortication. This can be done through a minimally invasive approach (video-assisted thoracoscopic surgery, or VATS) or through a traditional open incision (thoracotomy). A study of 217 consecutive patients with stage III empyema found that VATS and open surgery had comparable complication rates, recurrence rates, and overall hospital stays. However, adjusted analysis showed that the VATS approach reduced postoperative hospitalization by roughly one day compared to open surgery, and the conversion rate from VATS to open surgery was only 4.5%. For patients, VATS generally means less postoperative pain and a somewhat faster return to normal activity.
Complications of Untreated Empyema
The most significant long-term complication is fibrothorax, where the thick rind of scar tissue permanently restricts the lung from expanding. This leads to chronic shortness of breath and reduced exercise capacity that may not fully resolve even after surgery. In some cases, the trapped lung never fully re-expands.
Empyema can also lead to a bronchopleural fistula, an abnormal connection between the airway and the pleural space, which causes persistent air leaks and recurrent infections. If the infection isn’t controlled, it can spread to the bloodstream (sepsis), which is life-threatening. Chronic empyema that erodes through the chest wall, though rare, is called empyema necessitatis.
Recovery and Outlook
When caught early in the exudative stage, empyema responds well to antibiotics and drainage, and most people recover fully. The timeline varies, but you can generally expect to feel significantly better within one to two weeks of effective drainage, though the full antibiotic course and recovery may stretch over four to six weeks.
Later-stage empyema requiring surgery carries a longer recovery. After decortication, hospital stays typically last one to two weeks, and returning to full activity may take several weeks to months depending on overall health and how much lung function was compromised before surgery. Mortality rates for empyema vary widely depending on the patient’s age, underlying health, and how quickly treatment begins, but they generally range from about 5% to 15% in adults, with higher rates in elderly or immunocompromised patients.
The single most important factor in outcome is timing. Empyema that’s recognized and drained before it reaches the fibrinopurulent stage has the best prognosis. The longer pus sits in the pleural space, the more likely it is to organize into scar tissue that complicates both treatment and long-term lung function.