Resorptive (obstructive) atelectasis
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.
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Clinical presentation
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.
Pathology
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 circulating blood at a rate greater than it is replaced by fresh ventilated air. This causes volume loss in the affected lung. Volume loss may be minimal in distal airways obstruction due to the presence of collateral ventilation via the pores of Kohn.
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 ventilation from adjacent lung segments which causes a slightly distinct radiographic presentation. The speed of collapse is quicker if the patient is being given 100% oxygen 3.
Collapse occurs quickly if the obstruction is due to a luminal lesion that can act as a one-way valve.
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.
Etiology
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:
-
extra-luminal
- neoplasm
- lymphadenopathy
-
bronchial
- fibrotic stricture
- neoplasm
- spontaneous rupture 4
-
luminal
- mucus plugging
- pus
- bacterial pneumonia
- blood
- post-traumatic lung injury
- foreign body
- endobronchial intubation
Radiographic features
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 the 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 the unaffected lung
- mediastinal shift
- ipsilateral tracheal deviation
- ipsilateral shift of the heart
If volume loss is minimal and there is consolidation present, then the term drowned lung can be used to indicate transudate replacing the air in the collapsing lung. The transudate is rapidly cleared when the obstruction is removed, as is commonly seen in postoperative patients with mucous plugging.
Ultrasound
As a consequence of the cessation of ventilation, lung sliding is immediately abolished. In contrast to a pneumothorax, another cause of absent lung sliding, the presence of a lung pulse implies that the visceral and parietal pleura are still in apposition. As alveolar gas is absorbed, the lung parenchyma may assume a tissue-like echogenicity, with the following internal features 9;
-
air bronchograms
- unlike dynamic air bronchograms (present in e.g. pneumonia) these lentiform, branching echogenicities do not move with respiration 8
- referred to as static air bronchograms
-
fluid bronchograms 7
- tubular hypoechoic structures lacking vascular flow on color Doppler
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Airspace opacification
- airspace opacification
- differential diagnoses of airspace opacification
- lobar consolidation
-
atelectasis
- mechanism-based
- morphology-based
- lobar lung collapse
Chest
- imaging techniques
-
chest x-ray
-
approach
- adult
- pediatric
- neonatal
-
airspace opacification
- differential diagnoses of airspace opacification
- lobar consolidation
-
atelectasis
- mechanism-based
- morphology-based
- lobar lung collapse
- chest x-ray in the exam setting
- cardiomediastinal contour
- chest radiograph zones
- tracheal air column
- fissures
- normal chest x-ray appearance of the diaphragm
- nipple shadow
-
lines and stripes
- anterior junction line
- posterior junction line
- right paratracheal stripe
- left paratracheal stripe
- posterior tracheal stripe/tracheo-esophageal stripe
- posterior wall of bronchus intermedius
- right paraspinal line
- left paraspinal line
- aortic-pulmonary stripe
- aortopulmonary window
- azygo-esophageal recess
- spaces
- signs
- air bronchogram
- big rib sign
- Chang sign
- Chen sign
- coin lesion
- continuous diaphragm sign
- dense hilum sign
- double contour sign
- egg-on-a-string sign
- extrapleural sign
- finger in glove sign
- flat waist sign
- Fleischner sign
- ginkgo leaf sign
- Golden S sign
- Hampton hump
- haystack sign
- hilum convergence sign
- hilum overlay sign
- Hoffman-Rigler sign
- holly leaf sign
- incomplete border sign
- juxtaphrenic peak sign
- Kirklin sign
- medial stripe sign
- melting ice cube sign
- more black sign
- Naclerio V sign
- Palla sign
- pericardial fat tag sign
- Shmoo sign
- silhouette sign
- snowman sign
- spinnaker sign
- steeple sign
- straight left heart border sign
- third mogul sign
- tram-track sign
- walking man sign
- water bottle sign
- wave sign
- Westermark sign
-
approach
- HRCT
-
chest x-ray
- airways
- bronchitis
- small airways disease
-
bronchiectasis
- broncho-arterial ratio
- related conditions
- differentials by distribution
- narrowing
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tracheal stenosis
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-
bronchial stenosis
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tracheal stenosis
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- pulmonary edema
-
interstitial lung disease (ILD)
- drug-induced interstitial lung disease
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hypersensitivity pneumonitis
- acute hypersensitivity pneumonitis
- subacute hypersensitivity pneumonitis
- chronic hypersensitivity pneumonitis
- etiology
- bird fancier's lung: pigeon fancier's lung
- farmer's lung
- cheese workers' lung
- bagassosis
- mushroom worker’s lung
- malt worker’s lung
- maple bark disease
- hot tub lung
- wine maker’s lung
- woodsman’s disease
- thatched roof lung
- tobacco grower’s lung
- potato riddler’s lung
- summer-type pneumonitis
- dry rot lung
- machine operator’s lung
- humidifier lung
- shower curtain disease
- furrier’s lung
- miller’s lung
- lycoperdonosis
- saxophone lung
-
idiopathic interstitial pneumonia (mnemonic)
- acute interstitial pneumonia (AIP)
- cryptogenic organizing pneumonia (COP)
- desquamative interstitial pneumonia (DIP)
- non-specific interstitial pneumonia (NSIP)
- idiopathic pleuroparenchymal fibroelastosis
- lymphoid interstitial pneumonia (LIP)
- respiratory bronchiolitis–associated interstitial lung disease (RB-ILD)
- usual interstitial pneumonia / idiopathic pulmonary fibrosis (UIP/IPF)
-
pneumoconioses
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- non-fibrotic
-
lung cancer
-
non-small-cell lung cancer
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adenocarcinoma
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- minimally invasive tumors
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- described imaging features
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- large cell carcinoma
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- squamous cell carcinoma
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-
adenocarcinoma
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- preinvasive lesions
-
lung cancer invasion patterns
- tumor spread through air spaces (STAS)
- presence of non-lepidic patterns such as acinar, papillary, solid, or micropapillary
- myofibroblastic stroma associated with invasive tumor cells
- pleural invasion
- vascular invasion
- tumors by location
- benign neoplasms
- pulmonary metastases
- lung cancer screening
- lung cancer staging
-
non-small-cell lung cancer