Atelectasis is a partial or a complete collapse of a lung caused by complications arising out of respiratory illnesses. It develops when the alveoli, the tiny air sacs within the lungs, get deflated. Severe asthma, chest injuries, cystic fibrosis and congestion due to mucus in the airways are some of the common causes of atelectasis.

The severity of atelectasis depends on the amount of lung tissue affected which in turn depends on the underlying cause. In severe cases it can impair the exchange of oxygen and carbon dioxide in the lungs. Treatment depends on both the severity and the underlying cause.

Types of Atelectasis

There are two types of atelectasis, acute and chronic.

Acute atelectasis usually occurs after surgery involving the chest or abdomen. It may also occur after an injury to the chest. This type of atelectasis involves most of the alveoli in one or more regions of the lung, with the alveoli collapsing completely. Tight bandages, immobility, chest or abdominal pain or swelling and large doses of opioids or sedatives, increase the risk of acute atelectasis after surgery or injury. Premature babies may also develop acute atelectasis owing to a deficiency in the amount of surfactant in their lungs.

There are two types of chronic atelectasis, middle lobe syndrome or rounded atelectasis. Right middle lobe syndrome, also known as Andy Wilson’s Disease, involves the middle lobe of the right lung. This collapses and contracts due to pressure exerted on the bronchus by enlarged lymph glands. Pneumonia may set in leading to chronic inflammation, scarring and bronchiectasis.

Rounded atelectasis or folded lung syndrome involves the slow collapse of an outer portion of the lung. This is usually caused by scarring and shrinking of the pleura, the membranes covering the lung. The resulting rounded appearance on an x-ray image is sometimes mistaken for a tumor. Rounded atelectasis is commonly caused by asbestos related respiratory diseases.

  1. Janet Aldrich, Chapter 62 - Atelectasis, In: Lesley G. King, MVB, MRCVS, DACVECC, DACVIM, DECVIM-CA, Editor(s), Textbook of Respiratory Disease in Dogs and Cats, W.B. Saunders, Saint Louis, 2004, Pages 465-472, ISBN 9780721687063, 10.1016/B978-0-7216-8706-3.50066-9.