Atelectasis classification

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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1] ; Assistant Editor-in-Chief: Somal Khan, M.D.

Overview

Atelectasis may be an acute or chronic condition. In acute atelectasis, the lung has recently collapsed and is primarily notable only for airlessness. In chronic atelectasis, the affected area is often characterized by a complex mixture of airlessness, infection, widening of the bronchi (bronchiectasis), destruction, and scarring (fibrosis).

Classification

Acute Atelectasis

Acute atelectasis is a common postoperative complication, especially after chest or abdominal surgery. Acute atelectasis may also occur with an injury, usually to the chest (such as that caused by a car accident, a fall, or a stabbing). Atelectasis following surgery or injury, sometimes described as massive, involves most alveoli in one or more regions of the lungs. In these circumstances, the degree of collapse among alveoli tends to be quite consistent and complete. Large doses of opioids or sedatives, tight bandages, chest or abdominal pain, abdominal swelling (distention), and immobility of the body increase the risk of acute atelectasis following surgery or injury, or even spontaneously.

In acute atelectasis that occurs because of a deficiency in the amount or effectiveness of surfactant, many but not all alveoli collapse, and the degree of collapse is not uniform. Atelectasis in these circumstances may be limited to only a portion of one lung, or it may be present throughout both lungs. When premature babies are born with surfactant deficiency, they always develop acute atelectasis that progresses to neonatal respiratory distress syndrome.Adults can also develop acute atelectasis from excessive oxygen therapy and from mechanical ventilation, because of decreased effectiveness of surfactant.

Chronic Atelectasis

Chronic atelectasis may take one of two forms—middle lobe syndrome or rounded atelectasis. In middle lobe syndrome, the middle lobe of the right lung contracts, usually because of pressure on the bronchus from enlarged lymph glands and occasionally a tumor. The blocked, contracted lung may develop pneumonia that fails to resolve completely and leads to chronic inflammation, scarring, and bronchiectasis.

In rounded atelectasis (folded lung syndrome), an outer portion of the lung slowly collapses as a result of scarring and shrinkage of the membrane layers covering the lungs (pleura). This produces a rounded appearance on x-ray that doctors may mistake for a tumor. Rounded atelectasis is usually a complication of asbestos-induced disease of the pleura, but it may also result from other types of chronic scarring and thickening of the pleura.

There are several types of atelectasis according to their underlying mechanisms or the distribution of alveolar collapse; resorption, compression, microatelectasis and contraction atelectasis.