CONTENTS
- Definition of consolidation
- General causes of consolidation
- Anatomic distributions:
- Density:
- Consolidation-related signs:
- Questions & discussion
general definition of consolidation
- Consolidation refers to airspace disease that is dense enough to cause obscuration of the underlying lung vasculature (as opposed to ground glass opacity – which does not obscure the vasculature).
- Consolidation usually results from alveolar filling with various substances (e.g., cells, fluid, blood, purulence). However, extensive interstitial disease compressing the alveoli may rarely cause consolidation as well (e.g., “alveolar sarcoidosis”).
appearance of consolidation on chest radiography:
- Air bronchograms:
- These are frequently visible on chest radiography.
- Air bronchograms imply patency of the proximal airways. If the consolidation is due to large airway obstruction, fluid-filled airways occur which do not produce air bronchograms.
- Silhouette signs may occur if the consolidation contacts the border of a solid organ that is usually seen on X-ray due to an air/tissue interface. This will cause the disappearance of a structure that is normally visible. For example:
- Loss of a diaphragmatic border, due to lower lobe consolidation
- Loss of cardiac borders, due to middle lobe or lingular consolidation
- Loss of the left side of the aortic arch, due to apicoposterior left upper lobe consolidation.
- Loss of the right side of the aortic arch, due to anterior segment of the right upper lobe consolidation.
- The edges of the consolidated lung are usually poorly discernable on chest radiography, unless the consolidation is constrained by the pleura (e.g., complete consolidation of a lung lobe produces well-defined borders).
Below are some more common causes of consolidation.
infection (most common etiology)
- CAP (community acquired pneumonia):
- Fungal pneumonia.
- Mycobacteria (especially nontuberculous mycobacteria).
- Coxiella burnetii (Q-fever).
- Chlamydia psittaci (Psittacosis).
hemorrhage
- Secondary to focal disease (e.g., bronchiectasis or carcinoma).
- DAH (diffuse alveolar hemorrhage).
- Pulmonary infarction due to pulmonary embolism.
pulmonary edema, for example:
- Cardiogenic pulmonary edema.
- Diffuse alveolar damage.
- Papillary muscle dysfunction (asymmetric right upper lobe edema).
malignancy
- Postobstructive pneumonitis, due to endobronchial lesion.
- Lepidic adenocarcinoma.
- Lymphoma.
- Radiation induced lung injury.
interstitial/rare lung diseases
- OP (organizing pneumonia).
- CEP (chronic eosinophilic pneumonia).
- GPA (granulomatosis with polyangiitis).
- Sarcoidosis (“alveolar sarcoidosis”).
- Lipoid pneumonia.
other
- Atelectasis (including round atelectasis).
- Sequestration.
- Bacterial pneumonia (“round pneumonia”):
- Most common organisms identified: S. pneumoniae or H. influenzae.
- Usually no organism is identified.
- Other forms of pneumonia:
- COVID-19.
- Q fever (Coxiella burnetii).
- Fungal pneumonia.
- Septic embolism.
- Organizing pneumonia (OP).
- Round atelectasis.
- Neoplasms (especially adenocarcinoma or lymphoma).
Many disorders that cause diffuse consolidation are characterized by a central distribution. 📖
acute diffuse consolidation
- Edema:
- Cardiogenic pulmonary edema.
- Permeability (noncardiogenic) pulmonary edema.
- DAD (diffuse alveolar damage).
- Pneumonia:
- Severe bacterial pneumonia.
- Influenza virus pneumonia.
- Pneumocystis.
- CMV pneumonia.
- Diffuse alveolar hemorrhage (acute):
- Causes & radiology discussed further: 📖
chronic diffuse consolidation
- Pneumonia:
- CEP (chronic eosinophilic pneumonia).
- OP (organizing pneumonia).
- Lipoid pneumonia.
- Neoplasm:
- Primary or metastatic adenocarcinoma.
- Lymphoma.
- Pulmonary alveolar proteinosis.
causes of peripheral consolidation:
- Organizing pneumonia (this diagnosis may be supported by finding single/multiple nodules, or a reverse-halo sign).
- Eosinophilic pneumonia:
- CEP (chronic eosinophilic pneumonia).
- EGPA (eosinophilic granulomatosis with polyangiitis)(consolidations tend to have a lobular distribution, often associated with centrilobular nodules).(29286851)
- Simple pulmonary eosinophilia.
- HES (hypereosinophilic syndrome).
- Malignancy (lung adenocarcinoma, lymphoma).(26981938)
- Sarcoidosis (rarely).
- Infection should be considered, depending on the exact CT scan findings:
- Multiple septic emboli may produce a peripheral pattern.
initial investigations to consider might include:
- Blood count with differential (to evaluate for eosinophilia).
- IgE level.
- If concern for EGPA: ANCA, anti-MPO, and anti-PR3 titers.
- Appropriate infectious evaluation (e.g., CRP and procalcitonin levels).
radiologic features of low-density consolidation
- At the most basic level, consolidated tissue looks less dense than usual (darker).
- CT angiogram sign on a non-contrast CT: Low-density consolidation causes the pulmonary vessels to appear bright as they course through it. This looks like a CT angiogram – despite the fact that the patient hasn't received IV contrast.
- The density may be closer to fat density than soft-tissue density (e.g., roughly -20 to -150 Hounsfield units).(Murray 2022; 31812209)
causes of low-density consolidation
- Lipoid pneumonia.
- Postobstructive atelectasis (“drowned lung”), postobstructive pneumonia.
- Malignancy causing mucus accumulation in the parenchyma:
- Bronchoalveolar carcinoma.
- Lymphoma.
definition
- High-density consolidation is roughly defined as an airspace consolidation that has higher attenuation on CT scan than muscle. The normal attenuation of muscle is up to ~100-150 Hounsfield units, so any consolidation above ~100-150 Hounsfield units could be considered a high-density consolidation.
causes of high-density consolidation:
- Amiodarone exposure: Amiodarone causes an increase in the density of many tissues (including the liver and spleen). This increased density doesn't necessarily indicate that amiodarone is causing disease. However, high-density consolidation is certainly a reason to consider the possibility of amiodarone-induced pulmonary toxicity.
- Calcification:
- Pulmonary alveolar microlithiasis.
- MPC (metastatic pulmonary calcification).
- Talcosis (talc pneumoconiosis) causing progressive massive fibrosis.
- Iodinated oil embolism after lymphangiography.
- Aspiration or extravasation of contrast material.(32386651, 19204480)
A bulging fissure sign is associated with an enlarging consolidation, usually due to an aggressive lobar bacterial pneumonia (often with lung necrosis). Pathogens associated with a bulging fissure sign include:
- Klebsiella pneumoniae.
- Streptococcus pneumoniae.
- Pseudomonas aeruginosa.
- Staphylococcus aureus.
- Legionella pneumophila.
- Yersinia pestis.
- Mycobacterium tuberculosis. (31803267)
Alternative diagnoses which may masquerade as a bulging fissure sign include:
- Malignant infiltration (e.g., bronchoalveolar carcinoma).
- Lung abscess (although in many cases there may be a pathophysiological continuum between severe pneumonia and abscess formation).
description of the reversed halo sign
- Defined as a focal rounded area of ground-glass opacity surrounded by a more or less complete ring of consolidation.(24782557)
- The rim of consolidation doesn't necessarily need to be complete (it may be crescentic).
differential diagnosis of the reversed halo sign
Frequency statistics listed below are based on a systematic literature review by Maturu et al. (24782557) However, since this review is largely based on case reports, rare causes of reversed halo sign will be disproportionately overrepresented. The most common causes are underlined. In many situations, it's probable that the reversed halo sign may represent a component of superimposed organized pneumonia (OP) on top of another primary insult to the lung.
infection
- Tuberculosis (30/209).
- Paracoccidioidomycosis (27/203).
- Mucormycosis (23/209).
- Invasive pulmonary aspergillosis (8/203).
- H1N1 ARDS (3/203).
- COVID-19 (data unavailable).
- Uncommon causes:
- Histoplasmosis.
- Cryptococcosis.
- Pneumocystis.
- Psittacosis.
- Legionella.
inflammation
- Organizing pneumonia (66/209) is the classic cause of the reversed halo sign.
- Sarcoidosis (7/209).
- Vasculitis including GPA (granulomatosis with polyangiitis) in 4/209.
- Other less common causes:
- NSIP (nonspecific interstitial pneumonia).
- Lipoid pneumonia.
- Hypersensitivity pneumonitis.
- Lymphocytic interstitial pneumonia.
- Chronic eosinophilic pneumonia. (35038455)
pulmonary infarction
- Pulmonary embolism (19/209). 📖
malignancy
- Non-small cell lung cancer (3/209)(e.g., lepidic adenocarcinoma).
- Lymphomatoid granulomatosis.
- Lymphoma.
- Status post radiofrequency ablation.
- Radiation pneumonitis.
- Pulmonary tumor embolism.
approach to the reverse halo sign
The full differential diagnosis listed above should be considered. However, some common and early considerations may include the following:
(#1) consider the possibility of pulmonary embolism
- Radiographic features that support the possibility of PE:
- Wedge-shaped configuration.
- Lesion abuts the pleura.
- Pleural effusion is often seen.
- Consider obtaining a CT angiogram, if one hasn't already been done.
(#2) look for signs of granulomatous disease (“nodular reversed halo sign”)
- Radiologic features of reversed halo sign due to granulomatous disease:
- Wall is composed of a conglomeration of nodules (similar to the galaxy sign).
- Center of the lesion contains micronodules, with a stippled appearance.
- If seen, these features suggest:
- Usually either tuberculosis or sarcoidosis.
- Rarely, other granulomatous infections (e.g., cryptococcus).
- (This is described as a nodular reversed halo sign, with further discussion here: 📖)
(#3) if immunosuppressed, consider fungal infection
- For patients with significant immunosuppression, invasive fungal infection needs to be seriously considered (especially mucormycosis and aspergillosis).
- As the patient's net state of immunosuppression increases, they are more likely to have an infection and less likely to develop an inflammatory process.
- When selecting antifungal therapy for patients with a reverse halo sign, care should be taken to consider adequate coverage for mucormycetes (not solely Aspergillus).(22573292)
(#4) look for features of organizing pneumonia (OP)
- Features supporting OP include:
- (1) If a perilobular pattern is present, this is particularly suggestive of organizing pneumonia (see the section below on perilobular pattern).
- (2) The peripheral consolidation is typically thin in OP.(37289644)
- (3) The clinical illness in OP is often subacute/chronic.(Walker 2019)
- Additional discussion of radiological features of OP is here: 📖
characteristics of perilobular pattern
- This refers to polygonal or irregular opacities with poorly defined margins that occur surrounding a secondary pulmonary lobule.
- This is sometimes referred to as “septal thickening,” but perilobular opacities are more poorly defined than true septal thickening.(33280768)
- This pattern is often seen within the lower lung zones, frequently abutting the pleura.
- Perilobular opacities are always accompanied by consolidation or ground glass opacities within the same lung zone.(28106480)
- The processes that cause a perilobular pattern might represent a subset of the processes that cause a reverse halo sign.
various causes of a perilobular pattern
- OP (organizing pneumonia) is the most common cause – and in general the perilobular pattern is reasonably specific for this diagnosis. (Shepard 2019)
- CEP (chronic eosinophilic pneumonia).
- Myositis with anti-MDA5 antibody and rapidly progressive interstitial lung disease. (31178482)
- COVID-19.
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References
- 19204480 Marchiori E, Franquet T, Gasparetto TD, Gonçalves LP, Escuissato DL. Consolidation with diffuse or focal high attenuation: computed tomography findings. J Thorac Imaging. 2008 Nov;23(4):298-304. doi: 10.1097/RTI.0b013e3181788d39 [PubMed]
- 22573292 Marchiori E, Zanetti G, Hochhegger B, Irion KL, Carvalho AC, Godoy MC. Reversed halo sign on computed tomography: state-of-the-art review. Lung. 2012 Aug;190(4):389-94. doi: 10.1007/s00408-012-9392-x [PubMed]
- 24782557 Maturu VN, Agarwal R. Reversed halo sign: a systematic review. Respir Care. 2014 Sep;59(9):1440-9. doi: 10.4187/respcare.03020 [PubMed]
- 28212835 Raju S, Ghosh S, Mehta AC. Chest CT Signs in Pulmonary Disease: A Pictorial Review. Chest. 2017 Jun;151(6):1356-1374. doi: 10.1016/j.chest.2016.12.033 [PubMed]
- 31704148 Gruden JF, Naidich DP, Machnicki SC, Cohen SL, Girvin F, Raoof S. An Algorithmic Approach to the Interpretation of Diffuse Lung Disease on Chest CT Imaging: A Theory of Almost Everything. Chest. 2020 Mar;157(3):612-635. doi: 10.1016/j.chest.2019.10.017 [PubMed]
- 31812209 Pidcock W, Chau-Etchapare F, Murin S. A 65-Year-Old Man with Pulmonary Opacities and Worsening Cough. Chest. 2019 Dec;156(6):e117-e120. doi: 10.1016/j.chest.2019.05.041 [PubMed]
- 32386651 Yamamoto K, Ando K, Tanaka M, Yura H, Sakamoto N, Zaizen Y, Ashizawa K, Fukuoka J, Miyazaki Y, Mukae H. A 71-Year-Old Man With Dyspnea and Cough During Chemotherapy. Chest. 2020 May;157(5):e165-e171. doi: 10.1016/j.chest.2019.12.008 [PubMed]
- 35857938 Marchiori E, Hochhegger B, Zanetti G. Hypodense consolidation. J Bras Pneumol. 2022 Jul 15;46(3):e20200004. doi: 10.36416/1806-3756/e20200004 [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.