Atelectasis
Atelectasis is partial or complete collapse of a portion of the lung, in which the small air sacs (alveoli) deflate or fail to fully expand. It is a common imaging finding rather than a disease in itself and can range from small areas of incomplete expansion seen at the base of the lungs to collapse of an entire lobe. Atelectasis has many possible causes, including airway blockage, pressure from outside the lung, shallow breathing after surgery, and underlying lung disease. Most cases are mild and reversible, but persistent or severe atelectasis may signal an underlying problem that requires further evaluation.
What is it?
The lungs are made up of millions of tiny air sacs called alveoli, where oxygen and carbon dioxide are exchanged with the blood. Atelectasis occurs when some of these air sacs become deflated or fail to fully expand, causing a portion of the lung to lose volume. The collapsed area is no longer fully participating in normal gas exchange. Atelectasis can affect a small subsegment, an entire lobe, or, in severe cases, an entire lung.
There are several types and causes of atelectasis. Obstructive atelectasis occurs when an airway becomes blocked—commonly by a mucus plug, foreign body, tumor, or enlarged lymph node—so that air cannot reach the alveoli beyond the blockage and they collapse. Compressive atelectasis occurs when something outside the lung presses on it, such as a large pleural effusion (fluid around the lung), a pneumothorax (air around the lung), or a large chest mass. Adhesive atelectasis is related to problems with surfactant, the substance that keeps alveoli open, as can be seen in certain neonatal and adult conditions. Cicatricial (scarring) atelectasis results from chronic scarring of the lung, often from prior infection or interstitial lung disease. Subsegmental or “platelike” atelectasis is the most common finding on routine imaging and typically reflects shallow breathing, prolonged lying down, recent surgery, or splinting due to pain.
Symptoms depend on how much lung is affected and how quickly the collapse develops. Small areas of atelectasis are often asymptomatic and may be discovered incidentally on imaging. More significant atelectasis can cause cough, shortness of breath, increased work of breathing, chest discomfort, rapid heart rate, or low oxygen levels. Atelectasis after surgery—especially abdominal or thoracic surgery—is common and can contribute to postoperative fever and respiratory complications.
Imaging plays a central role in identifying atelectasis. Chest X-ray often shows characteristic findings such as displacement of nearby structures toward the collapsed area, increased density of the affected lung, and elevation of the diaphragm. CT of the chest provides more detailed information and is particularly helpful when the underlying cause is unclear or when an obstructing lesion is suspected. CT can show the location and extent of collapse, distinguish atelectasis from pneumonia or other lung disease, and identify masses, mucus plugs, or other obstructions. In cases where airway obstruction is suspected, bronchoscopy may be used both to confirm the cause and, in some cases, to treat it by removing a mucus plug or foreign body.
Important to Know
Treatment of atelectasis is directed at the underlying cause. Postoperative atelectasis often improves with deep breathing exercises, incentive spirometry, coughing, early mobilization, and adequate pain control to enable full inhalation. Atelectasis associated with pneumonia or other infection generally improves as the infection is treated. When airway obstruction is the cause, treatment may include bronchoscopy to remove mucus or a foreign body, treatment of any obstructing tumor, or therapy for an underlying airway disease. Atelectasis from compression—such as a large pleural effusion or pneumothorax—improves when the underlying problem is addressed.
Most cases of atelectasis are mild and resolve with conservative measures. However, persistent or unexplained atelectasis, particularly in an adult, may prompt additional evaluation to rule out an underlying obstructing lesion such as a lung tumor. Imaging findings are always considered alongside the patient’s symptoms and clinical context.
Red flag symptoms include severe or rapidly worsening shortness of breath, low oxygen levels, high fever with productive cough, coughing up blood, chest pain, or significant unintended weight loss. These warrant prompt medical evaluation, as they may indicate pneumonia, a significant airway obstruction, lung tumor, or another serious underlying condition.