Discussion Author: Samih Elakkad
Atelectasis is a common entity and has many different presentations. It is defined as a loss of lung volume due to collapse of the lung tissue. There are four general categories of atelectasis. They are passive, cicatricial, adhesive, and resorptive atelectasis. Passive is the most common type of atelectasis and it is due to the lungâ€™s natural elasticity. The most common cause of passive atelectasis is post-op because pain alters the breathing pattern and results in loss of volume. A pleural effusion is another cause of passive atelectasis since the effusion occupies lung space; the lung loses volume because of its elasticity in order to maintain a negative intrathoracic pressure. Other causes of passive atelectasis include pneumothorax, bullae, ascites, and neuromuscular diseases such as myasthenia gravis or spinal cord injury. Thoracic trauma can also cause passive atelectasis due to fractured ribs and splinting. The next type of atelectasis is cicatricial.
Cicatricial atelectasis is caused by an infiltrative process that causes diffuse volume loss. The two primary examples are idiopathic pulmonary fibrosis and sarcoidosis. The next type of atelectasis is adhesive atelectasis. It results from a surfactant dysfunction which increases the surface tension and causes alveolar collapse. Adhesive atelectasis is seen in respiratory distress syndrome of the newborn and acute respiratory distress syndrome in adults. Radiation exposure can also cause a surfactant dysfunction. The last type of atelectasis is resorption atelectasis and it is caused by bronchial obstruction. The most common cause of bronchial obstruction is a post-op mucous plug but cancer can also cause resorption atelectasis. The types of cancer that often cause bronchial obstruction include bronchogenic carcinoma, carcinoid tumor, cylindroma, mucoepidermoid carcinoma, metastatic breast carcinoma, metastatic melanoma, and metastatic lymphoma. Infectious causes of bronchial obstruction include tuberculosis, fungal, and plasma cell granuloma. Finally, an aspirated foreign body can cause bronchial obstruction . There are many causes of atelectasis and several signs on chest x-ray to recognize it.
There are direct and indirect signs of atelectasis. The direct signs are increased opacification of the lobe and displacement of the lung fissures. The indirect signs are mediastinal shift towards the side of collapse, narrowing of the intercostal spaces on the ipsilateral side, elevation of the ipsilateral hemidiaphragm, compensatory hyperinflation of the remaining aerated lung, and a silhouette sign of the adjacent structures. Another sign that is usually seen in upper lobe collapse is the juxtaphrenic peak, which is due to retraction of the lower end of the diaphragm due to an inferior accessory fissure or the inferior pulmonary ligament. Another sign seen in left upper lobe atelectasis is the luftsichel sign. It is due to hyperinflation of the superior segment of the left lower lobe that produces a radiolucency surrounding the aortic knob . It is important to recognize these signs because of the clinical significance of atelectasis.
Cancer should always be considered in the differential for atelectasis, especially if there is no obvious cause such as surgery, trauma, or pleural effusions. Post-surgical atelectasis is very common and can be prevented with incentive spirometry. Atelectasis is treated with antibiotics because infection often accompanies it .
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