Atelectasis: Definition, Symptoms, Causes, Mechanisms, Diagnosis, Classification and Treatment

It is the collapse or closure of a lung that results in reduced or absent gas exchange. It can affect part or all of a lung.

It is usually one-sided. It is a condition in which the alveoli are deflated at little or no volume, unlike the pulmonary consolidation, in which they fill with fluid.

It is often called a collapsed lung , although that term may also refer to pneumothorax.

It is a very common finding on chest x-rays and other radiological studies, and may be caused by normal exhalation or by various medical conditions.

Although it is often described as a collapse of lung tissue, atelectasis is not synonymous with a pneumothorax, which is a more specific condition that presents atelectasis.

Acute atelectasis can occur as a postoperative complication or as a result of a surfactant deficiency. In preterm infants, this leads to infant respiratory distress syndrome.

The term uses combined forms of atel + ectasia, from Greek: ἀτελής, “incomplete” + ἔκτασις, “extension”.

Signs and symptoms of atelectasis

It may not have signs and symptoms or may include:

  • Cough, but not prominent.
  • Chest pain (not common)
  • Difficulty breathing (fast and superficial).
  • Low oxygen saturation.
  • Pleural effusion (transduced type).
  • Cyanosis (late sign).
  • Incrise of cardiac frecuency.

It is a common misconception that atelectasis causes fever. A study of 100 postoperative patients followed by serial chest radiographs and temperature measurements showed that the incidence of fever decreased as the incidence of atelectasis increased.

A recent review article summarizing available published evidence on the association between atelectasis and postoperative fever concluded that there is no clinical evidence to support this doctrine.


The most common cause is postoperative atelectasis, which is characterized by splinting, that is, restricted breathing after abdominal surgery. Another common cause is pulmonary tuberculosis. Smokers and the elderly are also at greater risk.

Outside of this context, atelectasis involves some blockage of a bronchiole or bronchus, which can be inside the respiratory tract (foreign body, mucus plug), the wall (tumor, usually squamous cell carcinoma) or compressed from the outside (tumor, lymph node, tubercle).

Another cause is the poor diffusion of the surfactant during inspiration, which makes the surface tension is maximum, which tends to collapse the smaller alveoli.

Atelectasis can also occur during suction, since together with sputum, air is removed from the lungs.

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

Relaxation atelectasis (also called passive atelectasis) occurs when a pleural effusion or pneumothorax interrupts contact between the parietal pleura and the visceral pleura.

Mechanisms of pulmonary atelectasis

Atelectasis is one of the most frequent abnormalities in chest radiology and remains a daily diagnostic challenge.

Occasionally, atelectasis can be overlooked, particularly when pulmonary opacification is minimal or non-existent, and at other times it can be interpreted as another form of intrathoracic pathology, particularly pneumonia .

The direct signs of atelectasis are crowded pulmonary vessels, crowded air bronchograms and displacement of interlobar fissures.

Indirect signs of atelectasis are pulmonary opacification, elevation of the diaphragm, displacement of the trachea, heart and mediastinum, displacement of the hilus, compensatory hyperexpansion of the surrounding lung, approximation of the ribs and changing granulomas.

Whenever there are signs of volume loss on a chest x-ray, the radiograph should be interpreted as atelectasis.

By understanding the various mechanisms that lead to atelectasis, and considering the underlying conditions, the radiologist must be able to develop an adequate list of the possible causes of atelectasis.

The diagnosis of pneumonia atelectasis should be based on the presence of signs and symptoms of pneumonia together with the identification of pathogenic bacteria in the sputum, tracheal aspirates, or protected bronchoalveolar lavage or bronchial brush specimens rather than the radiographic identification of atelectasis only clinical .


Clinically significant atelectasis is usually visible on the chest radiograph; the findings may include pulmonary opacification and / or loss of lung volume. Post-surgical atelectasis will be bibasal type.

Thoracic computed tomography or bronchoscopy may be necessary if the cause of atelectasis is not clinically apparent.

Direct signs of atelectasis include displacement of interlobar fissures and mobile structures within the thorax, overinflation of the unaffected ipsilateral lobe or contralateral lung, and opacification of the collapsed lobe.


Atelectasis can be an acute or chronic condition. In acute atelectasis, the lung recently collapsed and is mainly notable only for lack of air.

In chronic atelectasis, the affected area is often characterized by a complex mixture of shortness of breath, infection, widening of the bronchi (bronchiectasis), destruction and scarring (fibrosis).

Abstraction atelectasis (resorption)

Absorption atelectasis is caused by reabsorption of the alveolar air distal to the obstructive airway lesions.

The atmosphere is composed of 78% nitrogen and 21% oxygen. Since oxygen is exchanged in the alveolar-capillary membrane, nitrogen is a major component of the alveolar inflation state.

If a large volume of nitrogen is replaced in the lungs with oxygen, the oxygen can be subsequently absorbed into the blood, reducing the volume of the alveoli, which produces a form of alveolar collapse known as absorption atelectasis.

Compression (relaxation) atelectasis

It is usually associated with the accumulation of blood, fluid or air within the pleural cavity, which mechanically collapses the lung.

This is a frequent case of pleural effusion, caused by congestive heart failure (CHF). The leakage of air into the pleural cavity (pneumothorax) also leads to a compression atelectasis.

Both passive atelectasis and compression atelectasis are caused by a secondary effect of compression of the normal lung by a large lung lesion.

In passive atelectasis, the lesion is intrapleural (such as a large pleural effusion or pneumothorax), but in compressed atelectasis, the problem is an intrapulmonary mass occupied by the primary space.

Atelectasis may develop due to retraction of the adjacent lung.

Cicatrization (contraction) atelectasis

It occurs when local or generalized fibrotic changes in the lung or pleura hinder expansion and increase elastic recoil during expiration. Causes include granulomatous disease, necrotizing pneumonia, and radiation fibrosis.

Chronic atelectasis

Chronic atelectasis can take one of two forms: middle lobe syndrome or rounded atelectasis.

Right middle lobe syndrome

In the right middle lobe syndrome, the middle lobe of the right lung contracts, usually due to pressure on the enlarged lymph node bronchi and occasionally a tumor.

The blocked and contracted lung can develop a pneumonia that does not resolve completely and produces chronic inflammation, scarring and bronchiectasis.

Rounded atelectasis

In rounded atelectasis (collapsed lung or Blesovsky’s syndrome ), an external portion of the lung slowly collapses as a result of scarring and contraction of the membrane layers covering the lungs (pleura), which would show visceral pleural thickening and entrapment of the lung. lung tissue

This produces a rounded appearance on X-rays that doctors may mistake for a tumor.

Rounded atelectasis is usually a complication of the pleura induced by asbestos, but may also be a consequence of other types of chronic scarring and thickening of the pleura.

Adherelectasia adhesive

Adhesive atelectasis is seen in premature babies who can not breathe spontaneously and in some babies after a few days of developing breathing difficulties; his lungs show areas in which the alveoli, or air sacs, do not expand with air.

These babies usually suffer from a disorder called respiratory distress syndrome, in which the surface tension within the alveolus is altered so that the alveoli collapse perpetually.

This is usually caused by a failure to develop active surface material (surfactant) in the lungs. Treatment for babies with this syndrome includes replacement therapy with surfactant.

Obstructive atelectasis

Obstructive atelectasis can be caused by foreign objects lodged in one of the main bronchial tubes, which causes the air trapped in the alveoli to be slowly absorbed by the blood.

It can also occur as a complication of abdominal surgery. The air passages in the lungs normally secrete a mucous substance to trap dust, soot and bacterial cells, which often enter with inhaled air.

When a person undergoes surgery, the anesthetic stimulates an increase in bronchial secretions. In general, if these secretions become too abundant, they can be expelled from the bronchi when coughing or exhaling strong air.

After abdominal surgery, breathing usually becomes more superficial due to the acute pain induced by respiratory movements, and the muscles under the lungs may weaken.

Mucous plugs can cause atelectasis. Other causes of obstruction include tumors or infections.

Atelectasis dependent on gravity

Gravity-dependent atelectasis is the result of alterations dependent on gravity in the alveolar volume.

It is a relatively benign form of atelectasis that usually does not require treatment. It is caused by small areas of your lung that can not fully expand when lying down.

The small portion of the lung that collapses under the influence of gravity usually expands on its own once you get up or change position. It is usually detected during a chest CT scan.

Minor dependent atelectasis

Minimal dependent atelectasis is a problem in which only a small portion of the lung collapses and, therefore, is not as severe as regular atelectasis. This condition usually affects the alveoli in the lower part of the lungs.

While anyone can suffer from minimal atelectasis, this problem is more likely to occur in elderly or bedridden people.

Staying in the same position for long periods of time often leads to poor ventilation of the lungs.

Patients who are in bed rest after having undergone surgery may also develop atelectasis or atelectasis dependent if they are not made to move approximately every hour or so.

The risks of this condition are also much higher in severely overweight people, since their lungs do not expand properly when they remain in one position for a long time.

Because minimal atelectasis affects only a small part of the lungs, the symptoms are usually not very serious.

Most patients only become aware of the condition when they undergo an imaging test to rule out the possibility of another medical problem.

If you experience these symptoms, your doctor may do a physical exam before you are asked to have tests like an x-ray, an ultrasound, or a chest CT scan.

Although minimal dependent atelectasis is not a serious condition, it should be reviewed and treated by a doctor without delay.

Mild atelectasis dependent

If the lungs are partially affected, this condition is called mild dependent atelectasis. Mild dependence often does not affect the quality of life. If the condition is mild, although the lungs are damaged, it does not affect the quality of life.

When the condition is not so severe, you may not even feel the symptoms. In the event that atelectasis is severe, organs tend to be deprived of oxygen and may cause additional complications.

Mild subsegmental atelectasis is a type of atelectasis in which the left lobe of the lungs is affected. In this type, linear fissures appear in the lung and appear below the chest radiographs.

The diagnosis of atelectasis depends on the cause. In adults, it is usually temporary and resolves without treatment as soon as the condition that triggers atelectasis is recovered.

If the lungs remain deflated for a longer period, it can be difficult for the lungs to clear the mucus. This delay could cause infections such as pneumonia.

Atelectasis in children or children can be fatal, especially if they affect a large part of the lungs. People with lung diseases such as emphysema can also be easily affected with atelectasis.

Considering that atelectasis is usually a mild type of this condition, the symptoms are usually not present.

When present, symptoms usually occur while lying down and may include shortness of breath, chest pain and coughing.

Atelectasia lobar

Lobar atelectasis is a common problem caused by a variety of mechanisms that include atelectasis due to resorption due to airway obstruction, passive atelectasis due to hypoventilation, compressive atelectis due to abdominal distention, and adhesive atelectasis due to increased surface tension.

However, studies based on evidence about the management of lobar atelectasis are lacking. The examination of air bronchograms on a chest radiograph may be useful in determining if obstruction of the proximal or distal airway is involved.

Chest physiotherapy, nebulized DNase, and possibly fiberoptic bronchoscopy may be useful in patients with mucosal airway obstruction.

In passive and adhesive atelectasis, positive end-expiratory pressure can be a useful adjunct to treatment.

Atelectasia segmentaria

Segmental atelectasis refers to the collapse of one or several segments of a pulmonary lobe . It is a morphological subtype of pulmonary atelectasis. It is best seen on computed tomography and its radiographic appearance can range from a thin linear to a wedge-shaped opacity and then does not rest on an interlobar fissure.

Atelectasia subsegmental

It affects only the part of a lung distal to an occluded segmental bronchus.

Subsegmental atelectasis is a type of atherosclerosis in which the lung volume decreases as a result of obstruction in the subsegmental bronchus or in a small bronchus.

Subsegmental atelectasis often occurs due to the presence of a tiny foreign body in the bronchus. It is more common in children, where small foods such as grains and peanuts can lodge in the bronchi during ingestion.

Subsegmental atelectasis is usually mild and produces no symptoms that may cause discomfort to the patient. However, in some cases it can cause symptoms such as coughing, shortness of breath. The cough is not productive and pirates. A very small amount of mucus is expelled.

Flat atelectasis

Plate-like atelectasis is also known as discolectric or subsegmental atelectasis. The obstruction of small bronchi produces atelectasis of the plaque. Hypoventilation, pulmonary embolism and lower respiratory tract infection are some of the common factors that cause the obstruction.

If the lungs can not fully expand and fill the air, atelectasis occurs. This can be caused by factors that prevent deep breathing and coughing and blockage of the airways. The obstruction of the bronchus is the main cause of atelectasis. It is common after surgery.

Linear or discoid atelectasis

Linear atelectasis is said to occur when a portion of the lungs away from the bronchus has collapsed. And the collapsed portion is linear because it is all together.

Discoid atelectasis is one of those types of atelectasis. Discoid atelectasis refers to a small area or small segment of the lungs that is affected by the condition.

On a chest x-ray, discoid atelectasis will appear as a disc or shadow similar to a plaque in the lungs.

This disc can be linear or horizontal in its position. Discolecular or platelet atelectasis is diagnosed and treated in a manner very similar to other types of atelectasis.

The symptoms of discoid atelectasis as with most other types of atelectasis are often confused with other diseases.

Symptoms such as breathing difficulties, chest pain and cough are general enough to make the diagnosis of the disease problematic.

Only with a chest x-ray or a chest CT can a doctor confirm your diagnosis of atelectasis.

When the area of ​​collapse is small, there can often be no symptoms or signs and the condition can simply be resolved over time.

However, in severe cases, the symptoms can affect a person’s breathing and can be life-threatening if not treated in time.


The treatment is aimed at correcting the underlying cause. Postsurgical atelectasis is treated by physiotherapy, focusing on deep breathing and stimulating cough.

An incentive spirometer is often used as part of breathing exercises. Walking is also highly recommended to improve lung inflation.

People with chest deformities or neurological conditions that cause shallow breathing for prolonged periods can benefit from mechanical devices that help their breathing.

One method is continuous positive pressure in the airways, which supplies air or oxygen under pressure through a nasal or facial mask to help ensure that the alveoli do not collapse, even at the end of breathing.

This is useful, since partially inflated alveoli can expand more easily than collapsed alveoli. Sometimes additional respiratory support is needed with a mechanical ventilator.

The primary treatment for acute massive atelectasis is correction of the underlying cause. A blockage that can not be eliminated by coughing or suctioning the airways can often be removed by bronchoscopy.

Antibiotics are given for an infection. Chronic atelectasis is often treated with antibiotics because infection is almost inevitable.

In certain cases, the affected part of the lung can be surgically removed when recurrent or chronic infections become disabling or hemorrhage is important.

If a tumor blocks the airways and relieves the obstruction by surgery, radiation therapy, chemotherapy, or laser therapy can prevent the progression of atelectasis and develop recurrent obstructive pneumonia .