Atelectasis is the partial or complete collapse of lung tissue due to deflation of the air sacs, while pneumothorax is the presence of trapped air in the space between the lung and the chest wall. Both can make breathing difficult and both show up on chest imaging as something wrong with the lung, but they arise from fundamentally different problems. Atelectasis is about the lung tissue itself losing volume from the inside; pneumothorax is about air pressing on the lung from the outside. The distinction matters because treatments diverge sharply, and in some cases, one condition directly causes the other.
How Each Condition Works
Think of the lung as a sponge sitting inside a sealed container (the chest cavity). In a healthy person, the sponge stays expanded because the pressure inside the chest cavity is slightly negative compared to the air inside the lung. That pressure difference keeps the lung inflated against the chest wall.
In atelectasis, the air sacs within the lung lose their air and flatten. This can happen because something blocks the airway feeding them (a mucus plug, a tumor, or an inhaled object), because the lung tissue is being squeezed from outside (by fluid, a mass, or trapped air), or because the air sacs lack the slippery coating called surfactant that normally keeps them from sticking shut. The result is a patch of lung, or sometimes an entire lobe, that simply isn’t participating in gas exchange anymore.
In pneumothorax, air leaks into the pleural space, the thin gap between the lung and the chest wall. That leaked air disrupts the normal negative pressure holding the lung open, and the lung partially or fully collapses on the affected side. The air can get there from inside (a ruptured blister on the lung surface) or from outside (a stab wound, a broken rib, or a needle puncture during a medical procedure).
Where They Overlap and Where They Don’t
Here is where clinicians sometimes have to think carefully: a large pneumothorax can cause atelectasis. When enough air accumulates in the pleural space, it compresses the lung so forcefully that sections of lung tissue collapse. In a reported neonatal case, a preterm infant with a massive pneumothorax developed a large area of compression atelectasis, and the lung re-expanded only after the trapped air was drained from the pleural cavity.1PubMed Central. Case Report: Neonatal Massive Pneumothorax Resulting in Compression Atelectasis Treated by Ultrasound-Guided Pleural Puncture Therapy So the two conditions are not always either/or. Sometimes pneumothorax is the cause and atelectasis is the consequence.
Atelectasis also changes the physics of the chest in ways that affect how air and fluid distribute themselves. When part of the lung collapses, the local pleural pressure shifts, and any pneumothorax or fluid collection in the chest will tend to migrate toward the collapsed area.2PubMed. Effects of lobar atelectasis on the distribution of pleural effusion and pneumothorax This can produce unusual patterns on imaging that make diagnosis harder.
What Causes Each One
The causes of atelectasis break into a few broad categories. The most common is obstruction of an airway: mucus plugs after surgery, inhaled foreign bodies in children, or tumors narrowing a bronchus. Compression atelectasis happens when something outside the lung pushes on it, whether that’s pleural fluid, a large tumor, or air from a pneumothorax. Adhesive atelectasis occurs when surfactant is missing or dysfunctional, a situation that affects premature infants most dramatically. In preterm babies born before about 28 weeks, severe surfactant deficiency leads to widespread atelectasis, poor oxygen exchange, and the condition known as respiratory distress syndrome.3European Respiratory Review. Pulmonary surfactant in newborn infants and children Atelectasis also develops routinely during general anesthesia, when the combination of muscle relaxation, altered breathing patterns, and high oxygen concentrations causes portions of the lung to collapse.4PubMed Central. Perioperative Pulmonary Atelectasis: Part II. Clinical Implications
Pneumothorax causes split into spontaneous and traumatic. Primary spontaneous pneumothorax tends to occur in tall, thin young men who smoke. The leading theory is that small air-filled blisters called blebs form on the lung surface, particularly near the top of the lung, and one of these blebs eventually ruptures. Risk factors include cigarette smoking, low body mass index, a family history of spontaneous pneumothorax, and connective tissue abnormalities.5European Respiratory Review. Spontaneous pneumothorax: epidemiology, pathophysiology and cause Secondary spontaneous pneumothorax happens in people who already have lung disease. The most frequent underlying conditions are COPD with emphysema, cystic fibrosis, tuberculosis, lung cancer, and HIV-associated pneumonia.5European Respiratory Review. Spontaneous pneumothorax: epidemiology, pathophysiology and cause Intravenous drug use adds its own layer of risk: injected substances can cause blister-like damage in the lung tissue, and the infections associated with needle sharing (like HIV) further raise the odds.6PubMed Central. Primary spontaneous pneumothorax due to high bleb burden Traumatic pneumothorax can result from blunt chest injuries, penetrating wounds, or medical procedures that accidentally nick the lung.
How the Symptoms Compare
Both conditions produce shortness of breath and can cause chest discomfort, which is part of why they’re sometimes confused. But the presentation has some characteristic differences.
Pneumothorax usually comes on suddenly. A person might feel a sharp, stabbing pain on one side of the chest and rapidly become short of breath. If the air leak is large, the affected side of the chest may look slightly more inflated, and breath sounds are diminished or absent when a clinician listens with a stethoscope. In a tension pneumothorax, where air keeps entering the pleural space but can’t escape, pressure builds until it starts pushing the heart and major blood vessels to the opposite side. This is a true emergency: blood pressure drops, the heart rate spikes, and the patient can deteriorate within minutes.
Atelectasis tends to be more subtle, especially when it involves a small area. A patient recovering from surgery might develop a low-grade fever and mild shortness of breath. On examination, the affected side of the chest may expand less than the other side, breath sounds are reduced over the collapsed area, and the area may sound dull when tapped. Crackling sounds may be heard as the lung begins to re-inflate. When atelectasis involves an entire lobe or lung, the symptoms are more dramatic: significant breathlessness, low oxygen levels, and sometimes a visible shift of the windpipe toward the collapsed side, because the lung is pulling structures inward rather than pushing them away (the opposite of what happens in a large pneumothorax).
Why Imaging Can Be Tricky
On a standard upright chest X-ray, the two conditions generally look quite different. A pneumothorax appears as a dark area at the edge of the lung where no lung markings are visible, because that space is filled with air that shouldn’t be there. Atelectasis appears as a white or hazy area, because the collapsed lung tissue is denser than normal inflated lung.
The challenge arises when both conditions are present at the same time, especially in patients who are lying flat. In supine chest X-rays, a pneumothorax doesn’t pool at the top of the chest like it does in an upright film; instead, the air layers out in front of the lung, creating a more diffuse, harder-to-spot change. When that diffuse extra lucency overlaps with the increased density of underlying atelectasis, the two effects can partially cancel each other out, producing a vague, nonspecific opacity that doesn’t clearly look like either condition alone.7PubMed Central. Pneumothorax and Atelectasis Appearing as a Non-Specific Opacity on a Supine Infant’s Chest X-Ray
Ultrasound has become a valuable bedside tool for sorting this out, but it has its own pitfalls. One of the hallmark signs clinicians look for is “lung sliding,” the shimmering, back-and-forth movement visible on ultrasound as the lung glides against the chest wall during breathing. In pneumothorax, lung sliding disappears because air in the pleural space separates the lung from the wall. But in certain types of atelectasis, lung sliding can also disappear, because the lung is so collapsed and motionless that no gliding occurs. A case report documented this exact confusion: ultrasound showed absent lung sliding and an air-artifact pattern that initially suggested pneumothorax, but no “lung point” (the spot where normal lung meets the pneumothorax boundary) could be found, because the real diagnosis was atelectasis.8PubMed Central. Not all abolished lung sliding are pneumothorax: the case of a particular lung atelectasis The lung point is a useful distinguishing sign; its presence strongly supports pneumothorax, and its absence should prompt clinicians to consider other explanations.
Treatment Paths
The treatments for these two conditions differ because the underlying problems are different. Atelectasis treatment is about getting the collapsed lung tissue to re-expand from the inside. For the garden-variety atelectasis that develops after surgery, this usually means deep breathing exercises, incentive spirometry (a device that encourages slow, sustained inhalation), early ambulation, and sometimes chest physiotherapy. In a study of patients who had coronary artery bypass grafting, roughly two-thirds developed some degree of atelectasis despite using incentive spirometry, underscoring how common the problem is after chest and abdominal surgery.9Iranian Red Crescent Medical Journal. Comparison of the Effect of Inhalation and Intermittent Inhalation-Exhalation Incentive Spirometry on Dyspnea Severity and Atelectasis in Patients undergoing Coronary Artery Bypass Graft When a mucus plug is the culprit, bronchoscopy can be used to physically clear the blockage. For surfactant-deficient premature infants, administering artificial surfactant directly into the airway is the standard intervention.10NeoReviews. Core Concepts: Respiratory Distress Syndrome
Pneumothorax treatment is about removing the trapped air from the pleural space. Small pneumothoraces in stable patients may be managed conservatively, simply monitoring the patient while the body gradually reabsorbs the air. For larger or symptomatic ones, the air needs to be removed. The two main options are needle aspiration (inserting a needle or small catheter and drawing the air out) and chest tube drainage (placing a tube that stays in the chest and continuously drains air until the leak seals). A meta-analysis comparing the two approaches found that needle aspiration shortened hospital stays by about a day and a half on average and reduced the rate of hospitalization, with no difference in immediate success or one-year recurrence.11PubMed Central. Chest tube drainage versus needle aspiration for primary spontaneous pneumothorax: which is better? A randomized trial confirmed that needle aspiration achieved higher immediate success rates and shorter hospital stays for both primary and secondary spontaneous pneumothorax, though by one week the outcomes between the two methods were equivalent.12European Respiratory Journal. Randomised comparison of needle aspiration and chest tube drainage in spontaneous pneumothorax For patients with small primary spontaneous pneumothorax and minimal symptoms, conservative management (observation without drainage) has been shown to produce comparable resolution and recurrence rates to chest tube drainage, with fewer complications during treatment.13PubMed Central. Chest Tube Drainage Versus Conservative Management as the Initial Treatment of Primary Spontaneous Pneumothorax: A Systematic Review and Meta-Analysis
When Pneumothorax Keeps Coming Back
One of the frustrating aspects of primary spontaneous pneumothorax is its tendency to recur. A study of 286 patients found that those who presented with complete lung collapse had a recurrence rate of about 70%, compared to roughly 39% in those with partial collapse.14PubMed Central. Complete atelectasis of the lung in patients with primary spontaneous pneumothorax Complete atelectasis at the initial presentation was also associated with more persistent air leaks and a higher rate of needing surgery. In that same study, nearly 79% of the complete-collapse group ultimately underwent video-assisted thoracoscopic surgery (VATS), compared to about 45% of the partial-collapse group.14PubMed Central. Complete atelectasis of the lung in patients with primary spontaneous pneumothorax
VATS has become the workhorse surgical approach for recurrent pneumothorax. The procedure typically involves removing the blebs or blisters responsible for the leak and then inducing the lung to stick to the chest wall (pleurodesis) so that even if a new bleb forms, there’s no space for air to accumulate. Multiple techniques exist for pleurodesis, including talc application and other agents. Studies report durable results: in one series, VATS bullectomy with pleurodesis produced no recurrences over a median follow-up of more than three years.15PubMed Central. Simultaneous Viscum pleurodesis and video-assisted thoracic surgery (VATS) bullectomy in patients with primary spontaneous pneumothorax Talc pleurodesis delivered via VATS has similarly been described as a durable treatment for recurrent cases.16PubMed. Spontaneous pneumothorax rates following video-assisted thoracoscopic talc pleurodesis with or without resection of macroscopic bullous disease Long-term follow-up after surgical pleurectomy (a more traditional open procedure) has shown no significant impairment in lung function afterward, which is reassuring for younger patients who may live decades after their surgery.17PubMed. The surgical treatment of spontaneous pneumothorax by parietal pleurectomy
Mediastinal Shift and When to Worry
One imaging finding that understandably alarms patients and their families is mediastinal shift, where the central structures of the chest (heart, major blood vessels, windpipe) appear pushed to one side on an X-ray. In pneumothorax, this usually means the trapped air is pushing everything away from the affected side. In atelectasis, the shift goes in the opposite direction, pulling structures toward the collapsed lung. Understanding which way the shift goes actually helps clinicians tell the conditions apart.
A common assumption is that any mediastinal shift on a pneumothorax X-ray signals a tension pneumothorax requiring emergency needle decompression. A review of 176 pneumothorax presentations found that 30 patients had mediastinal shift on their initial chest X-ray, but none of those 30 were clinically in tension or required emergency needle decompression; all were managed with standard chest tube insertion.18PubMed Central. Is mediastinal shift on chest X-ray of pneumothorax always an emergency? True tension pneumothorax is a clinical diagnosis, not just a radiographic one. The two patients in that study who did have clinical tension pneumothorax were identified and treated before they ever got to the X-ray machine. The lesson: mediastinal shift on imaging is worth attention, but it’s the patient’s overall condition, not the X-ray alone, that determines urgency.
Premature Infants and Surfactant
Newborns, especially premature ones, occupy a unique space in this discussion because they’re at elevated risk for both conditions. Extremely preterm infants lack surfactant, the substance that reduces surface tension inside air sacs and keeps them from collapsing. Without it, atelectasis develops rapidly after birth, leading to poor oxygen transfer and respiratory failure.19Paediatrics and Child Health. The pathophysiology of respiratory distress syndrome in neonates Administering exogenous surfactant has been a transformative treatment, but these same fragile infants also face a higher risk of pneumothorax, partly because mechanical ventilation can overdistend their stiff lungs, and partly because the disease itself creates uneven ventilation that puts extra stress on some lung regions.
When both conditions occur simultaneously in a neonate, diagnosis becomes especially challenging. Standard X-ray findings may be ambiguous, and the clinical picture can change rapidly. Lung ultrasound has emerged as a valuable tool in neonatal intensive care units because it can be performed at the bedside, involves no radiation, and can often distinguish between the two conditions in real time.1PubMed Central. Case Report: Neonatal Massive Pneumothorax Resulting in Compression Atelectasis Treated by Ultrasound-Guided Pleural Puncture Therapy
AI-Assisted Detection on Chest X-Rays
Missing a pneumothorax on a chest X-ray is a recognized problem, particularly in emergency departments where images are read quickly and often by less experienced providers. Artificial intelligence software designed to flag pneumothorax has shown strong standalone performance, with one system achieving an area under the curve of 0.965, meaning it was very accurate at distinguishing X-rays with and without pneumothorax. When AI assistance was provided to readers of varying experience levels, performance improved significantly across all groups, with the biggest gains seen among junior readers, the frontline clinicians who are often the first to review these films.20PubMed Central. Impact of AI Assistance in Pneumothorax Detection on Chest Radiographs Among Readers of Varying Experience AI support also narrowed the performance gap between experienced and inexperienced readers, which has practical implications for smaller hospitals and overnight shifts where a radiologist may not be immediately available. These tools don’t yet reliably distinguish between pneumothorax and the mimics that can look similar on imaging, including certain forms of atelectasis, but they add a safety net for the most time-sensitive diagnosis.
Diving and Altitude Exposure
Both atelectasis and pneumothorax have relevance to environments involving pressure changes. Divers face a particular risk of pneumothorax during ascent, when air in the lungs expands as surrounding water pressure drops. If a diver holds their breath or ascends too quickly, the expanding air can rupture lung tissue and escape into the pleural space, a form of pulmonary barotrauma. People with a history of spontaneous pneumothorax are generally advised against recreational scuba diving because existing blebs could rupture under pressure changes. Absorption atelectasis can also occur in divers who breathe high concentrations of oxygen; the oxygen is absorbed so quickly from the air sacs that they collapse if not replenished by incoming gas at the same rate. This same mechanism is why breathing 100% oxygen during anesthesia can worsen atelectasis, and it’s one reason anesthesiologists increasingly use blended gas mixtures during surgery.