We often see the term “atelectasis” on chest film results, yet little do people really know about it. This article aims to enlighten us and give us more information and insights regarding that matter.

What is Atelectasis?

Atelectasis comes from the Greek words ateles and ektasis with the literal meaning “incomplete expansion”. It pertains to collapse, either complete or partial, of the lung, which may subsequently cause decreased volume and diminished gas exchange. [1, 2, 3]


An image representing Atelectasis, or collapsed lung.



Understanding Atelectasis

In a normal lung, air is breathed in and travelled to the air sacs (alveoli), where it transcends to the blood through the capillaries. These alveoli remain open and filled with air during respiration to facilitate adequate gas exchange.

However, during atelectasis, the lung, or a part of it, collapses. A number of air sacs do not inflate, unable to do their function and fill with air. If only a small part of the lung is affected, clinical manifestations may not be noted, and the rest of the lung can provide enough oxygen to compensate. But if this affects a major percentage of the lungs, the whole body may not acquire sufficient oxygen, a state detrimental for us humans. [ 4, 5, 6]

 atelectasis process

An illustration showing the normal lung: Air when inhaled travels from the nose to the lungs, it traverses the circulation by passing through alveoli or the air sacs.


 atelectatic lung in comparison

The normal and the atelectatic lungs: in comparison. With volume decreased in the collapse lungs, sufficient gas exchange may not be feasible.


Atelectatic Lung Types

A frequent respiratory pathology, atelectasis may be brought about by different mechanisms and is classified into numerous types. [7, 8, 9, 10]

1.      Resorptive Atelectasis

This type of atelectasis is mainly due to resorption of gas found on the alvoeli distal to the obstruction. In the early phases of which, blood circulation continues, the oxygen and nitrogen gases are thus absorbed. Air present distal to the obstruction is absorbed, en route to the pulmonary circulation, causing nonventilated alveoli to collapse.  It is common among those patients with mucus plug blockages.

 resorptive atelectasis

This image exemplifies resorptive atelectasis, in which an obstruction blocks the normal gas exchange. Air distal to the blockage causes collapse and atelectasis of the lung.


2.      Adhesive Atelectasis

Surfactant, a substance produced by the lung to reduce surface tension, is lacking.  Its loss causes the lungs to collapse and become atelectatic. This is best exemplified by the respiratory distress syndrome among newborns (hyaline membrane disease), but can also be seen among adults in cases of simple pneumothorax, hypoventilation, diaphragmatic dysfunction, pulmonary embolism, and adult respiratory distress syndrome.

atelectasis ards

This chest xray film shows adhesive atelectasis in a patient with adult respiratory distress syndrome. Deficiency in surfactant brought about collapse and atelectasis.


 Respiratory distress syndome

This illustrates Hyaline Membrane Disease and the alveolar collapse due to lack of surfactant.




An xray film of a newborn with Respiratory Distress Syndrome: note the lung collapse, a type of adhesive atelectasis.


3.      Compressive/ Relaxation Atelectasis

Usually seen in tension pneumothorax, pleural effusion, abdominal distention and intrathoracic lesions, this occurs when pleural pressure seizes the lungs, keeping it near the chest wall. As the pressure disappears, the lung eventually recoils, causing atelectasis. This is also coined as passive atelectasis.

 compression atelectasis

This image shows compression or relaxation atelectasis, as demonstrated by a patient with pleural effusion.


4.      Contraction/Cicatricial Atelectasis

This is usually encountered in patients with pulmonary fibrosis. Fibrotic changes in the lung or pleura inhibit expansion of the lungs. Alveoli get shut in by the scar, causing atelectasis.

 Atlectasis contraction

The photo depicts fibrotic changes in the lung causing lung collapse and atelectasis, particularly the contraction or cicatricial type.



Risk Factors

Factors increasing the risk for developing atelectasis are as follows: [1, 5, 8, 11]

  • Extremes of age: either advanced age or premature birth
  • Surgery: usually those involving the  upper abdomen and chest
  • Pulmonary conditions: pulmonary edema, pneumothorax, pleural effusion, tuberculosis, chronic obstructive pulmonary disease and cystic fibrosis.
  • Tumors: lymphomas, lung carcinoma, and metastases to the pulmonary system
  • Rib fractures and other chest injuries
  • Heart failure
  • Conditions limiting mobility and physical activity such as spinal cord injury and other severe illnesses
  • Neurological diseases: multiple sclerosis, amyotrophic lateral sclerosis and myasthenia gravis
  • Foreign body inhalation
  • Anesthesia use
  • Obesity
  • Asbestos exposure
  • Narcotics and sedatives

Atelectasis: Signs and Symptoms

As stated previously, atelectasis may or may not be manifested. Small areas of collapse maybe  surmounted by the larger areas with normal gas exchange, thus no signs and symptoms would be visible. Larger lung collapses diminish the oxygen supply throughout the body, causing a number of clinical manifestations, such as tachypnea, difficulty of breathing, shortness of breath, frequent coughing bouts, fever, tachycardia, chest pain and cyanosis. Upon physical examination, decreased breath sounds may be noted on auscultation, along with dullness upon percussion. [ 1, 8, 11]

Atelectasis: Clues to Its Diagnosis

After a comprehensive history and physical examination, diagnostics are to be done for confirmation of the diagnosis of atelectasis.

1.      Chest xray films

Chest radiographic findings include airless appearing part of the lungs. The trachea and heart shifts towards the affected lung. There may even be elevation of the diaphragm, a narrowed space interval among the ribs, and movement of the oblique fissures.

This diagnostic procedure can also identify the presence of obstruction and of underlying lung conditions such as pneumonia.

A number of radiologic signs specific for atelectasis may also be seen [5, 7, 12, 13].

Bowing Sign

The oblique fissure of the lung bends over, as seen in the lateral view. This is usually seen in the left upper lung atelectasis.

 atelectasis bowing sign

The arrow shows bowing forward of the fissure (Bowing sign), in a lateral view xray of a patient with atelectasis.


Double Lesion Sign

First described by Felson, it involves atelectasis of the right upper and right lower lung fields, but spares the right middle lung. When present, primary bronchogenic carcinoma can be ruled out.

Golden S Sign

This upper lobe collapse is usually caused by a centrally located mass. Either S shaped curve or a reverse S shaped contour can be observed in the film.

atelectasis s curve

An S shaped curve in seen in a patient with upper lobe atelectasis


Open Bronchus Sign

This can usually be seen in an adhesive atelectasis.  An obstruction completely blocks a middle bronchus. On the other hand, the bronchi within the opacified lung are open; hence the term.

 open bronchus

An open bronchus sign in the presence of adhesive atelectasis.



2.      Chest CT scan

This is done for further evaluation of a possible atelectasis. It can identify not only tumors, but even enlarged lymph nodes as causes of obstruction. [5]

3.      Bronchoscopy

Flexible bronchoscopy can be utilized as both a diagnostic and therapeutic method. It identifies the cause of obstruction and helps clear the blockages for immediate relief. [2]



The main goal in the treatment of atelectasis is the re-expansion of the collapsed lung. This can be done according to etiology. Tumors can be treated with surgery, chemotherapy or radiation. Foreign body and mucosal obstruction can be relieved by bronchoscopy and drainage. [2, 5]

Other treatment methodologies include chest physiotherapy and medications such as inhaled bronchodilators, steroids and acetylcysteine [8]. Deep breathing exercises and Positive Expiratory Pressure (PEP) devices can also be used [14].


Small areas of atelectasis are usually not dangerous. The remaining parts of the lung, which is normal and adequately functioning, may compensate and provide for the collapsed part. Thus, supply enough oxygen for the whole body. [14, 15]

Large areas of atelectasis, on the other hand, may be dangerous, with the prognosis depending on the underlying illnesses. Those with life threatening carcinomas may have worse prognosis than those with simple post-operative atelectasis.  [ 6, 15]



2. Madappa, T. et al. Atelectasis. 2012 March.
3. Wedding, M. et al.(2005). Medical Terminology Systems: A Body Systems Approach. Philadelphia, Pa: FA Davis Company.
5. Eldridge, L. Atelectasis. 2012 Oct.
9. Woodring, J. et al. Types and Mechanisms of Pulmonary Atelectasis. Journal of Thoracic Imaging. 1996.


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