A simple pneumothorax is a collection of air trapped between the lung and the chest wall that causes part or all of the lung to collapse. Unlike its more dangerous counterpart, a tension pneumothorax, the trapped air in a simple pneumothorax does not build up enough pressure to push the heart and major blood vessels out of position. That distinction is what makes it “simple,” though the experience of having one is anything but.
How Air Gets Trapped in the Chest
Your lungs sit inside a double-layered membrane called the pleura. Normally, the two layers of this membrane stay pressed together with only a thin film of fluid between them, creating a seal that keeps your lungs inflated. When air leaks into that space, the seal breaks and the lung on that side partially or fully deflates, like letting air out of a balloon inside a jar.
Air reaches the pleural space through one of two routes: a break in the lung’s surface that lets air escape from inside the lung, or an injury to the chest wall that lets outside air in. Both create the same result, but the underlying cause determines how the pneumothorax is classified and treated.
What Causes It
Simple pneumothorax falls into three broad categories based on what triggered the air leak.
Primary spontaneous pneumothorax happens without any obvious lung disease or injury. It typically affects tall, thin young adults, often men in their 20s and 30s. The cause is usually the rupture of small air-filled blisters on the lung surface called blebs. These can pop during normal activity or even at rest, with no warning.
Secondary spontaneous pneumothorax occurs in people who already have an underlying lung condition. Chronic obstructive pulmonary disease (COPD) is the most common culprit, but conditions like cystic fibrosis, tuberculosis, and certain infections can also weaken lung tissue enough for it to give way. These cases tend to be more serious because the lungs are already compromised.
Traumatic pneumothorax results from a direct injury to the chest, whether from a car accident, a fall, a stab wound, or even a medical procedure. Placement of a central IV line near the collarbone is the most common procedure-related cause. Lung biopsies, ventilator use, and even acupuncture on the chest wall have been reported as triggers.
Symptoms to Recognize
The hallmark symptom is sudden, sharp chest pain on one side that worsens when you breathe in. Most people also feel an immediate sense of breathlessness that seems out of proportion to what they’re doing. In small pneumothoraces, these may be the only symptoms, and some people mistake the pain for a pulled muscle or a heart problem.
Larger collapses, those affecting more than about 15% of the lung, produce more noticeable signs. You may feel your heart racing, notice that breathing takes more effort, or feel like you can’t get a full breath. A doctor listening with a stethoscope would hear diminished or absent breath sounds on the affected side, and tapping on the chest produces a hollow, drum-like sound instead of the normal dull tone.
How It Differs From a Tension Pneumothorax
The word “simple” in the name is a clinical distinction, not a statement about severity. In a simple pneumothorax, the trapped air stays put. It may cause discomfort and breathing difficulty, but it doesn’t compress the structures in the center of the chest.
A tension pneumothorax is a medical emergency. It develops when air continues to enter the pleural space with each breath but can’t escape, creating a one-way valve effect. Pressure builds until it pushes the heart, major blood vessels, and windpipe toward the opposite side of the chest. This compression reduces blood flow back to the heart, causing a dangerous drop in blood pressure. Signs include severe respiratory distress, low blood pressure, the windpipe visibly shifting to one side, and bulging neck veins. A simple pneumothorax can progress to tension if the air leak continues unchecked, which is one reason even “simple” cases need monitoring.
How It’s Diagnosed
A standard chest X-ray is the most common way to confirm a pneumothorax. On the image, the collapsed portion of the lung appears as a visible line with no lung markings beyond it, and the space between that line and the chest wall looks darker than normal because it’s filled with air instead of lung tissue.
Ultrasound has become an increasingly valuable tool, especially in emergency settings where speed matters. In a healthy lung, ultrasound shows a shimmering, sliding motion where the two layers of the pleura glide against each other with breathing. When air is trapped in the pleural space, that sliding disappears. On a specific ultrasound mode called M-mode, normal lung produces a grainy “seashore” pattern, while a pneumothorax produces stacked horizontal lines resembling a barcode, known as the stratosphere sign. When ultrasound detects absent lung sliding along with certain echo patterns, it identifies hidden pneumothoraces with about 95% sensitivity. A finding called the “lung point,” where normal sliding lung meets the border of the collapsed area, is 100% specific for pneumothorax and can even help estimate its size.
Treatment Options
How a simple pneumothorax is managed depends primarily on its size and how much it affects your breathing.
Observation. Small pneumothoraces that cause minimal symptoms can often be managed with monitoring alone. You’d typically stay in a medical facility for several hours while repeat imaging confirms the air pocket isn’t expanding. Supplemental oxygen speeds reabsorption of the trapped air because it changes the gas pressure gradient, pulling air out of the pleural space and back into the bloodstream. The British Thoracic Society’s current guidelines support conservative management for primary spontaneous pneumothoraces regardless of size, as long as symptoms are minimal and vital signs are stable.
Needle aspiration. For larger or more symptomatic cases, a doctor can insert a needle or small catheter into the pleural space to suction out the trapped air. This is a relatively quick bedside procedure. It works well for many first-time spontaneous pneumothoraces, particularly when the distance from the lung apex to the top of the chest cavity is 3 cm or more, or the collapse covers roughly 15 to 20% of the lung area.
Chest tube drainage. When aspiration doesn’t fully re-expand the lung, or when the air leak is ongoing, a chest tube may be placed. This is a flexible tube inserted between the ribs and connected to a one-way drainage system that lets air escape continuously until the lung re-inflates and the leak seals. Most chest tubes stay in for a few days.
Recovery and Recurrence
Most people recover from a first-time simple pneumothorax within one to two weeks after the lung has fully re-expanded. During recovery, you’ll likely be told to avoid strenuous activity and heavy lifting until follow-up imaging confirms the lung is staying inflated.
The biggest concern after recovery is recurrence. Studies report that 20 to 60% of people who have a primary spontaneous pneumothorax will have another one, with one large retrospective study of 153 patients finding a recurrence rate of 54%. Most recurrences happen within the first one to two years. After a second episode, the likelihood of a third increases substantially, which is why surgical intervention to prevent further episodes is often recommended after a recurrence.
Air travel and scuba diving both pose risks after a pneumothorax because changes in atmospheric pressure cause trapped gas to expand. Most medical organizations recommend waiting at least 7 to 14 days after imaging confirms the pneumothorax has fully resolved before flying commercially. Scuba diving carries an even greater risk due to the extreme pressure changes involved, and many specialists advise against returning to diving at all without surgical correction of the underlying cause.