Resorptive or obstructive atelectasis is a form of lung collapse that is due to obstruction of the airways supplying a lung segment or lobe. It is a term used to distinguish atelectasis identified on imaging based on the underlying pathophysiology to guide diagnosis.
The presentation of patients with atelectasis depends on the underlying cause. However, breathlessness is common if there is significant lung collapse and infective symptoms can be present if there is co-existing sepsis.
As the name implies, in this form of atelectasis there is partial or complete bronchial obstruction which leads to poor ventilation of the airways supplied. As ventilation between the distal air spaces and the trachea is disrupted the residual air in the affected lung is resorbed by the vessels at a rate greater than it is replaced by fresh ventilated air. This causes volume loss in the affected lung.
The rate at which atelectasis progresses depends on whether there is obstruction of a lobar or segmental bronchus. Lobar obstruction manifests as lobar atelectasis. In segmental atelectasis there is often a degree of collateral ventillation from adjacent lung segments which causes a slightly distinct radiographic presentation.
Eventually there can be sequestration of local lung secretions over time and areas of significant atelectasis are prone to become infected. Hence, this type of collapse is frequently seen with co-existing consolidation.
The causes of resorption (obstructive) atelectasis can be thought of in terms of where the obstructing lesion arising from with respect to the bronchial lumen:
- fibrotic stricture
Plain radiograph / CT
The imaging features of atelectasis are similar on plain radiographs and CT with more detail being available on the CT:
- increased density at site of atelectasis
- loss of normal thoracic silhouettes
- displacement of the fissures toward the area of atelectasis
- upward displacement of ipsilateral hemidiaphragm
- crowding of pulmonary vessels and bronchi affected area
- compensatory hyperinflation of unaffected lung
- mediastinal shift
- ipsilateral tracheal deviation
- ipsilateral shift of the heart
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