CONTENTS
- Basics
- Clinical presentation
- Types and causes of atelectasis
- Radiology
- Bronchoscopy
- Management
- Additional/related topics
- Questions & discussion
abbreviations used in the pulmonary section: 6
- ABPA: Allergic bronchopulmonary aspergillosis 📖
- AE-ILD: Acute exacerbation of ILD 📖
- AEP: Acute eosinophilic pneumonia 📖
- AFB: Acid fast bacilli
- AIP: Acute interstitial pneumonia (Hamman-Rich syndrome) 📖
- ANA: Antinuclear antibody 📖
- ANCA: Antineutrophil cytoplasmic antibodies 📖
- ARDS: Acute respiratory distress syndrome 📖
- ASS: Antisynthetase syndrome 📖
- BAL: Bronchoalveolar lavage 📖
- BiPAP: Bilevel positive airway pressure 📖
- CEP: Chronic eosinophilic pneumonia 📖
- CF: Cystic fibrosis 📖
- COP: Cryptogenic organizing pneumonia 📖
- CPAP: Continuous positive airway pressure 📖
- CPFE: Combined pulmonary fibrosis and emphysema 📖
- CTD-ILD: Connective tissue disease associated interstitial lung disease 📖
- CTEPH: Chronic thromboembolic pulmonary hypertension 📖
- DAD: Diffuse alveolar damage 📖
- DAH: Diffuse alveolar hemorrhage 📖
- DIP: Desquamative interstitial pneumonia 📖
- DLCO: Diffusing capacity for carbon monoxide 📖
- DRESS: Drug reaction with eosinophilia and systemic symptoms 📖
- EGPA: Eosinophilic granulomatosis with polyangiitis 📖
- FEV1: Forced expiratory volume in 1 second 📖
- FVC: Forced vital capacity 📖
- GGO: Ground glass opacity 📖
- GLILD: Granulomatous and lymphocytic interstitial lung disease 📖
- HFNC: High flow nasal cannula 📖
- HP: Hypersensitivity pneumonitis 📖
- IPAF: Interstitial pneumonia with autoimmune features 📖
- IPF: Idiopathic pulmonary fibrosis 📖
- IVIG: Intravenous immunoglobulin 📖
- LAM: Lymphangioleiomyomatosis 📖
- LIP: Lymphocytic interstitial pneumonia 📖
- MAC: Mycobacterium avium complex 📖
- MCTD: Mixed connective tissue disease 📖
- NIV: Noninvasive ventilation (including CPAP or BiPAP) 📖
- NSIP: Nonspecific interstitial pneumonia 📖
- NTM: Non-tuberculous mycobacteria 📖
- OHS: Obesity hypoventilation syndrome 📖
- OP: Organizing pneumonia 📖
- OSA: Obstructive sleep apnea 📖
- PAP: Pulmonary alveolar proteinosis 📖
- PE: Pulmonary embolism 📖
- PFT: Pulmonary function test 📖
- PLCH: Pulmonary Langerhans cell histiocytosis 📖
- PPFE: Pleuroparenchymal fibroelastosis 📖
- PPF: Progressive pulmonary fibrosis 📖
- PVOD/PCH Pulmonary veno-occlusive disease/pulmonary capillary hemangiomatosis 📖
- RB-ILD: Respiratory bronchiolitis-associated interstitial lung disease 📖
- RP-ILD: Rapidly progressive interstitial lung disease 📖
- TNF: tumor necrosis factor
- UIP: Usual interstitial pneumonia 📖
- Atelectasis is defined as volume reduction of lung tissue, due to reduced aeration.
- The clinical significance of atelectasis varies widely depending on the cause, configuration, and severity. For example, a small amount of dependent atelectasis is commonly seen, with minimal clinical significance. Alternatively, lobar atelectasis may be the cause of respiratory failure.
potential symptoms
- Respiratory dysfunction (e.g., hypoxemia, tachypnea).
- Cough.
potential exam signs
- Focally reduced breath sounds.
- Focal wheeze may occur if there is a focal airway obstruction.
obstructive (resorptive) atelectasis
- Endobronchial lesion:
- Malignancy:
- Lung cancer (especially squamous cell carcinoma).
- Carcinoid tumor.
- Bronchial metastasis from distant cancer. 📖
- Benign lesions (e.g., hamartoma, fibroepithelial polyp).
- Endobronchial granuloma (tuberculosis, histoplasmosis, sarcoidosis).
- Malignancy:
- Material in bronchus:
- Broncholithiasis (erosion of calcified lymph node into the bronchus, usually due to histoplasmosis).
- Foreign body.
- Mucus plugging:
- Post-surgical.
- Asthma, or allergic bronchopulmonary aspergillosis.
- Chronic bronchitis, bronchiectasis.
- Pneumonia.
- Cystic fibrosis.
- Other causes of bronchus dysfunction:
- Bronchial stenosis.
- Bronchomalacia. (30131839)
- Extrinsic compression of bronchus (neoplasm, lymphadenopathy, aortic aneurysm, cardiac enlargement).
- Malpositioned endotracheal tube.
compressive (aka passive, aka extrinsic, aka relaxation atelectasis)
- Pleural disease:
- Pneumothorax.
- Pleural effusion.
- Organomegaly:
- Cardiomegaly.
- Aortic aneurysm.
- Tumor.
- Skeletal deformity.
- Diaphragmatic elevation.
- Adjacent space-occupying lung lesion (e.g., bulla).
adhesive or patchy atelectasis (widespread collapse of alveoli due to surfactant deficiency)
- Pulmonary embolism (focal ischemia distal to pulmonary emboli may cause subsegmental or segmental atelectasis).
- Acute radiation pneumonitis 📖 (within the radiation field; 1-6 months after therapy).
- Smoke inhalation injury.
- Viral pneumonia.
intrinsic fibrosis of the lung tissue (cicatricial or contraction atelectasis)
- Causes include:
- Interstitial lung disease (e.g., idiopathic pulmonary fibrosis).
- Chronic infection (e.g., tuberculosis).
- Radiation fibrosis.
- More on radiology & etiology of fibrosis: 📖
(#1) atelectasis can make things small and confusing
- Atelectasis involves deflation of the lung.
- As atelectasis becomes more complete, the deflated lung becomes smaller. This may make atelectasis relatively unimpressive radiographically, because the atelectatic lung doesn't occupy much space.
- 💡 Atelectasis may cause hypoxemia and respiratory dysfunction which appears disproportionately severe as compared to a gross view of the chest radiograph. For example, lower lobe atelectasis may cause loss of a substantial volume of lung parenchymal function without looking very dramatic.
(#2) imaging of mucus plugging
- Immediately after mucus plugging occurs, imaging may be relatively normal (gas hasn't been reabsorbed from the obstructed lung, so its size is normal).
- 💡 If a patient develops acute hypoxemia and respiratory distress with an unimpressive chest radiograph, consider mucus plugging (along with pulmonary embolism).
- Collapse of multiple lobes that aren't contiguous with one another suggests multiple mucus plugs.
(#3) air bronchograms
- The presence of air bronchograms implies that the airways remain open.
- Air bronchograms suggest that atelectasis is due to compression, adhesion, or contraction (not airway obstruction).
- The presence of an air bronchogram may suggest that patients are less likely to respond to chest physiotherapy (because the airway is already open). (453712)
(#4) contrast CT appearance of atelectasis
- On contrast CT scan, atelectasis will appear relatively hyperdense. In contrast, lobar consolidation often has a density similar or lower than skeletal muscle. (Walker 2019)
frontal radiograph
- Silhouette signs:
- Right superior mediastinal border is lost. With complete collapse, the right upper lobe becomes very small, so this may appear as a subtle widening of the superior mediastinum. (Walker 2019)
- Shifts:
- Minor fissure is shifted up and rotates towards the mediastinum.
- Right hila is shifted up.
- Trachea and aorta may be pulled to the right.
- Juxtaphrenic peak may be visible in the diaphragm (aka diaphragmatic tenting).
- This is a pointy configuration of the diaphragm due to upper lobe collapse, in the context of an inferior accessory fissure.
- Juxtaphrenic peak may result from right upper lobe atelectasis or resection (or less commonly, middle lobe atelectasis). (Walker 2019)
lateral radiograph
- Compressed lung generates an indistinct, upside-down triangle.
- Major fissure is displaced anteriorly.
reverse-S sign of Golden
- This may be caused by an obstruction of the right upper lobe due to a large central mass.
- Half of the “S” is generated by the superior displacement of the minor fissure.
- Half of the “S” is generated by medial convexity of a central tumor mass (figure below).
- Although classically associated with the right upper lobe, this configuration of atelectasis can occur in any lobe due to a central mass. (Walker 2019)
differential diagnosis
- Right upper lobe atelectasis can be mistaken for a paratracheal mass on frontal radiograph.
frontal radiograph
- The right heart border is indistinct (due to silhouetting by the collapsed right middle lobe).
- The right middle lobe itself generates a hazy opacity abutting the heart. This may be relatively subtle.
lateral radiograph
- The collapsed right middle lobe generates a triangular opacity or linear band.
- The transverse fissure may be pulled downwards so that it slopes at an angle parallel to the oblique fissure.
right middle lobe syndrome (RMLS)
basics
- The right middle lobe is particularly prone to the development of atelectasis for several reasons: (31060710)
- The right bronchus is longer with a narrow angle and orifice, which is often prone to obstruction.
- The right middle lobe has less effective collateral ventilation, as compared to other lobes. Consequently, obstruction of the right middle lobe bronchus tends to cause lobar collapse.
- The right middle lobe bronchus is surrounded by lymph nodes, rendering it vulnerable in patients with bulky lymphadenopathy.
- Right middle lobe syndrome is a term which refers to various disorders that cause recurrent or persistent atelectasis or consolidation of the right middle lobe.
- A similar process can affect the lingula, albeit less often. (Rosado-De-Christenson 2022)
causes of right middle lobe syndrome include
- [1] Anatomic obstructive processes:
- Endobronchial lesion:
- Endobronchial malignancy (e.g., carcinoid, lung cancer, endobronchial metastasis).
- Foreign body.
- Broncholith.
- Inspissated mucus (allergic bronchopulmonary aspergillosis, or even just asthma).
- Extrinsic compression:
- Hilar lymphadenopathy (e.g., tuberculosis, histoplasmosis, sarcoidosis, silicosis).
- Severely enlarged right atrium may compress the RML bronchus. (Rosado-de-Christenson 2022)
- Benign abnormality of right middle lobe anatomy.
- Bronchial stenosis (e.g., following endobronchial tuberculosis, radiotherapy). (31060710)
- Endobronchial lesion:
- [2] Non-obstructive (often with localized bronchiectasis)
- Indolent infection:
- Especially nontuberculous Mycobacteria.
- Tuberculosis.
- Indolent infection:
clinical presentation of right middle lobe syndrome
- The right middle lobe is relatively small. The functional loss of the right middle lobe is often well tolerated clinically (without causing significant dyspnea or hypoxemia). These patients often have chronic, asymptomatic collapse of the right middle lobe.
- Symptoms may result from:
- Secretion production (e.g., coughing).
- Infection (e.g., bronchiectasis).
investigation
- Prior radiographs should be reviewed to determine chronicity (these sometimes reveal ongoing atelectasis for years).
- CT scan is the front-line investigation.
- Bronchoscopy may be needed to exclude malignancy.
management
- Treatment depends on the etiology.
- Obstruction may be treated with interventional pulmonology therapies (e.g., balloon dilation, laser therapy).
- The right middle lobe is small, so resection is generally well tolerated. Consequently, surgical resection is a consideration if other treatments fail and symptoms are persistent.
frontal radiograph
- Opacity over the left hemithorax (mostly the upper and middle lung fields).
- The opacity may have sharp borders that can look like a pneumothorax.
- Shifts:
- Mediastinum, trachea, and aorta may be shifted to the left.
- Left diaphragm may be elevated (normally, the right hemidiaphragm should be higher, or the diaphragms should be even). (27627477)
- Juxtaphrenic peak may occur in the left diaphragm.
- Silhouetting:
- Loss of the left heart border.
- Loss of left border of the superior mediastinum can occur.
- Aortic knob appearance varies:
- (1) The aortic knob may be silhouetted and invisible.
- (2) Luftsichel sign:
- The hyperinflated left superior segment of the lower lobe may be interposed between the mediastinum and the collapsed upper lobe. This creates a crescentic lucency that extends downward from the lung apex, reaching between the aortic arch and the collapsed left upper lobe.
- Typically this is associated with centrally obstructing lung cancer. (Rosado-de-Christenson 2022)
- Differential diagnosis of the luftsichel sign: (Rosado-de-Christenson 2022)
- Anterior herniation of a hyperinflated right lung across the midline.
- Pneumomediastinum.
- Medial pneumothorax.
- Bullous lung disease adjacent to the aortic arch.
lateral radiograph
- The left upper lung collapses into a vertical pancake.
- The right lung may sometimes herniate across the mediastinum, creating a retrosternal air space (which lies interposed between the sternum and the collapsed left upper lung).
- The major fissure is pulled forward, almost parallel to the chest wall.
Lower lobes on both sides have similar anatomy, so atelectasis causes similar patterns.
frontal radiograph
- Wedge-shaped density caused by collapsed lower lobe.
- On the left: this may overlie the heart, sometimes silhouetting the descending aorta.
- This density causes silhouetting of the medial hemidiaphragm border and the descending pulmonary artery.
- Shifts:
- Heart and mediastinum may be displaced towards atelectatic lobe. In left lower lobe atelectasis, rotation of the heart causes a loss of concavity of the left heart border (“flat waist sign”).
- Diaphragm may be shifted up.
- Hilum is pulled downwards. In right lower lobe collapse, the transverse fissure is pulled downwards.
lateral radiograph
- Collapsed lung may be seen as a triangular density. However, in many cases this is indistinct (causing only a hazy increased density over the lower spine).
- Silhouetting of the diaphragm (especially the posterior diaphragm).
- The major fissure is pulled posteriorly.
- Hemidiaphragm may be elevated.
- Diagnostic bronchoscopy may be indicated for lobar atelectasis, especially if:
- Atelectasis fails to respond to less invasive therapies.
- Etiology is unclear.
- Atelectasis is longstanding.
- Some patients may benefit from removal of mucus plugs or foreign body via bronchoscopy.
treatment of any underlying cause
- For example, atelectasis due to endobronchial tumor may sometimes benefit from endobronchial debulking by interventional pulmonology.
multimodal analgesia (for patients with pain)
- Management of atelectasis in a nonintubated patient often requires that the patient be able to comfortably breathe deeply, cough, and participate in chest physiotherapy.
- Multimodal analgesia may help promote comfort, without excessive sedation (which may exacerbate atelectasis). For example, the addition of acetaminophen and pain-dose ketamine to an opioid is often helpful. More on multimodal analgesia here: 📖
atelectasis due to mucus plugging
- Among hospitalized patients, mucus plugging is the most common cause of atelectasis.
- Initial therapy focuses on conservative measures:
- Increased airway pressure may promote lung inflation:
- For intubated patients, higher PEEP or APRV (Airway Pressure Release Ventilation) may be used to recruit lung.
- For nonintubated patients, CPAP or BiPAP with high expiratory pressure may be helpful.
- Chest physiotherapy and airway clearance may be helpful.
- Mobilization out of bed is useful, if this is possible.
- Conservative FiO2 administration will delay the absorption of inspired gas, thereby promoting lung inflation. (30528423)
- Upright positioning will tend to bring the diaphragm downwards, thereby improving lung inflation (especially of the lower lobes). For example, increasing the angle of the head of the bed to 60-degrees could theoretically be helpful. For patients with obesity, angulating the entire bed at a 60 degrees angle may be more useful than elevating solely the head of the bed (to avoid compression of the abdomen).
- Increased airway pressure may promote lung inflation:
- Bronchoscopy for removal of mucus plugs may be considered if other therapies fail. However, the results are generally disappointing (because the real problem isn't the mucus plugs themselves, but rather the overall conditions which led to the formation of mucus plugs).
- If present, air bronchograms indicate that airways are patent – so bronchoscopy is likely to be futile. (30528423)
- Bronchoscopy as an isolated therapy for the therapy of mucus plugging is frequently ineffective. If bronchoscopy is performed, it must be combined with additional measures (as outlined above).
- The only randomized trial evaluating bronchoscopy found that it didn't add anything as compared to respiratory therapy alone. (453712)
basics
- Round atelectasis generally occurs as a consequence of a highly inflammatory pleural effusion. The effusion initially causes compressive atelectasis of the adjacent lung. Inflammation and adhesions on the visceral pleura subsequently prevent the lung from re-inflating as the effusion resolves. The ultimate result is a small area of trapped lung due to visceral pleural fibrosis.
- Round atelectasis is a benign process that usually doesn't cause symptoms or physiologic dysfunction.
- Clinical significance of round atelectasis:
- (1) This may mimic a tumor, leading to diagnostic confusion and perhaps unnecessary procedures.
- (2) Round atelectasis may serve as a diagnostic indicator of chronic pleuritis.
causes of round atelectasis
Round atelectasis can potentially be caused by a broad variety of causes of chronic pleuritis. Examples include:
- BAPE (benign asbestos pleural effusion) is the classic etiology.
- Infection (especially tuberculosis).
- Uremic pleuritis.
- Hemothorax.
- Cardiothoracic surgery (e.g., CABG).
- Lupus pleuritis.
- Chemical pleurodesis (rare complication).
radiographic findings
lesion features
- Location:
- Peripherally located, often at the lung base.
- Posterior location is more common than anterior location. (Rosado-de-Christenson 2022)
- Atelectasis contacts the pleura, forming an acute angle.
- Multiple lesions may be present.
- Characteristics:
- Round or oval mass, usually ~2.5-5 cm in size.
- Peripheral edge is well-defined, but the hilar edge may be ill-defined. (Rosado-de-Christenson 2022)
- Intrinsic punctate calcifications are seen in ~1/3 of cases. (Rosado-de-Christenson 2022)
- Air bronchograms may be seen within the lesion in ~60% of cases. (Walker 2019)
associated abnormalities that may be seen
- “Comet tail” sign may be caused by crowded vessels and bronchi sweeping into and around the base of the atelectatic lung. This was ~83% sensitive and ~92% specific for round atelectasis in one series. (29090995)
- 💡 Look for the comet tail sign in different projections (e.g., coronal, sagittal). This sign may be more obvious in an unusual projection.
- Pleural abnormalities: (Rosado-de-Christenson 2022)
- Pleural thickening (~80%) may be adjacent to the lesion, and/or it may occur elsewhere in the thorax. (29090995)
- Pleural effusion (~60%).
- Pleural calcification (~40%).
- Hypertrophy of extrapleural fat may also occur, a feature reflective of chronicity. (Walker 2019)
differential diagnoses may include:
- Lung cancer.
- Pulmonary infarct.
- Localized fibrous tumor of the pleura. (Rosado-de-Christenson 2022)
diagnostic & therapeutic approach
diagnosis
- For patients with imaging that is highly suggestive of round atelectasis, serial imaging to establish stability may be reasonable (to help exclude malignancy). (29090995)
- PET/CT scan may also be helpful to evaluate for malignancy. Round atelectasis should have no PET avidity. (Rosado-de-Christenson 2022)
management
- Any underlying disorder may be treated (if still active).
- No treatment is indicated for the round atelectasis itself. The primary significance of diagnosing round atelectasis is often that the lesion can be left alone (rather than biopsied or resected).
Drowned lung refers to pneumonitis that occurs distal to bronchial obstruction. This leads to an airless, fluid-filled region of lung tissue.
radiologic findings:
- Dense opacification of a segment, lobe, or lung without air bronchograms. (Walker 2019)
- Bronchi may sometimes be seen as hypodense structures filled with mucus that run through the opacified lung tissue.
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References
- 27627477 Walker CM, Hobbs SB, Carter BW, Chung JH. Progressive Dyspnea with Cough. Ann Am Thorac Soc. 2016 Sep;13(9):1654-6. doi: 10.1513/AnnalsATS.201604-296CC [PubMed]
- 29090995 Newman TA, Takasugi JE, Matute-Bello G, Virgin JB, Backhus LM, Adamson R. Occam's Razor versus Hickam's Dictum. Ann Am Thorac Soc. 2017 Nov;14(11):1709-1713. doi: 10.1513/AnnalsATS.201701-087CC [PubMed]
- 30528423 Marini JJ. Acute Lobar Atelectasis. Chest. 2019 May;155(5):1049-1058. doi: 10.1016/j.chest.2018.11.014 [PubMed]
- 31060710 Henson T, Matayeva E, Chua W, Iqbal J. A 76-Year-Old Woman With Incidental Right Middle Lobe Atelectasis. Chest. 2019 May;155(5):e137-e140. doi: 10.1016/j.chest.2018.10.030 [PubMed]
Books:
- Shah, P. L., Herth, F. J., Lee, G., & Criner, G. J. (2018). Essentials of Clinical pulmonology. In CRC Press eBooks. https://doi.org/10.1201/9781315113807
- Shepard, JO. (2019). Thoracic Imaging The Requisites (Requisites in Radiology) (3rd ed.). Elsevier.
- Walker C & Chung JH (2019). Muller’s Imaging of the Chest: Expert Radiology Series. Elsevier.
- Palange, P., & Rohde, G. (2019). ERS Handbook of Respiratory Medicine. European Respiratory Society.
- Rosado-De-Christenson, M. L., Facr, M. L. R. M., & Martínez-Jiménez, S. (2021). Diagnostic imaging: chest. Elsevier.
- Murray & Nadel: Broaddus, V. C., Ernst, J. D., MD, King, T. E., Jr, Lazarus, S. C., Sarmiento, K. F., Schnapp, L. M., Stapleton, R. D., & Gotway, M. B. (2021). Murray & Nadel’s Textbook of Respiratory Medicine, 2-Volume set. Elsevier.
- Fishman's: Grippi, M., Antin-Ozerkis, D. E., Cruz, C. D. S., Kotloff, R., Kotton, C. N., & Pack, A. (2023). Fishman’s Pulmonary Diseases and Disorders, Sixth Edition (6th ed.). McGraw Hill / Medical.