Radiography
Findings
Chest radiographs and CT scans show direct and indirect signs of lobar collapse. Direct signs include displacement of fissures and opacification of the collapsed lobe. Indirect signs include displacement of the hilum, a mediastinal shift toward the side of collapse, loss of volume in the ipsilateral hemithorax, elevation of the ipsilateral diaphragm, crowding of the ribs, compensatory hyperlucency of the remaining lobes, and silhouetting of the diaphragm or heart border.
Complete atelectasis
Complete atelectasis of an entire lung is characterized as follows: complete collapse of a lung leads to opacification of the entire hemithorax and an ipsilateral shift of the mediastinum. The mediastinal shift separates atelectasis from a massive pleural effusion (see Images 8 and 13).
RUL collapse
The collapsed RUL shifts medially and superiorly, resulting in elevation of the right hilum and the minor fissure. The RUL may also collapse laterally, producing a pleural-based opacity that may look like a loculated pleural effusion.
The minor fissure in an RUL collapse is usually convex at its superior aspect, but it may appear concave because of an underlying mass lesion. This is called the Golden sign of S (also known as the Golden S sign and the S sign of Golden).
Tenting of the diaphragmatic pleura, called the juxtaphrenic peak sign, is another helpful sign of RUL atelectasis (see Images 2, 15, and 17).14
RML collapse
RML collapse obscures the right heart border on a posteroanterior (PA) image. The lateral view shows a triangular opacity overlying the heart because the major fissure shifts upward and the minor fissure shifts downward. With worsening collapse, the opacity diminishes in size, and it may be barely perceptible (see Images 3 and 20).
RLL collapse
The collapsed RLL shifts posteriorly and inferiorly, resulting in a triangular opacity that obscures the RLL pulmonary artery. The major fissure, normally not visible on a PA radiograph, is evident with an RLL collapse. The superior mediastinal structure shifts to the right, causing a superior triangle sign. Laterally, the collapsed RLL obliterates the posterior one third of the right hemidiaphragm and projects as an opacity over the normally lucent area (see Images 4 and 21).
Concomitant RML and RLL atelectasis may appear as an elevated right hemidiaphragm or a subpulmonic effusion. An attempt to identify the fissures usually leads to the accurate diagnosis (see Image 19).
LUL collapse
An atelectatic LUL shifts anteriorly and superiorly. In one half of the cases, a hyperexpanded superior segment of the LLL is positioned between the atelectatic upper lobe and the aortic arch. This gives the appearance of a crescent of the aerated lung, called the luftsichel sign.
On PA views, an atelectatic LUL produces a faint opacity in the left upper hemithorax, obliterating the left heart border. On lateral views, the major fissure is displaced anteriorly behind the sternum (see Images 4, 6, and 9-11).
LLL collapse
On frontal views, an increased retrocardiac opacity obliterates the LLL pulmonary artery and the left hemidiaphragm. The hilar structures shift downward, and the rotation of the heart produces flattening of the cardiac waist, which is known as the flat-waist sign. The superior mediastinum may shift and obliterate the aortic arch; this is the top-of-the-aortic-knob sign.
On the lateral radiographs, an opacity silhouettes the posterior third of the left diaphragm, and an opacity is projected over the normally lucent area (see Images 5 and 14).
Rounded atelectasis
In cases of rounded atelectasis, segmental or subsegmental atelectasis occurs secondary to visceral pleural thickening and entrapment of the lung tissue.
Rounded atelectasis manifests as a subpleural mass, and bronchovascular structures radiate out of the mass toward the hilum. An associated parietal pleural plaque may be present. The swirl appearance of the bronchovascular shadows is called the comet-tail sign and establishes the diagnosis (see Image 22).15
Degree of Confidence
Chest radiography has the highest sensitivity when direct signs of atelectasis can be detected. More specifically, the identification of a displaced fissure is of significant advantage in diagnosing lobar collapse. The presence of several indirect signs further corroborates the direct signs in the diagnosis of atelectasis.
False Positives/Negatives
Modest loss of volume may occur secondary to lobar consolidation; this may lead to the erroneous diagnosis of lobar collapse.
A loculated pleural effusion or pleural effusion with passive collapse may be mistakenly identified as a collapse secondary to an endobronchial lesion. False-negative results may occur if the collapse does not involve the whole lobe; this situation may be secondary to an incompletely obstructive bronchial lesion or partial ventilation of the lobe.
Platelike atelectasis or postoperative atelectasis may often be missed on chest radiographs because it may be obscured by other thoracic structures. A false-negative diagnosis may also occur if the patient cannot take a full breath or if the anteroposterior or lateral chest radiograph is not available.
Computed Tomography
Findings
Radiographic changes of lobar collapse are more obvious on CT scans than on plain radiographs. CT scans are additionally helpful in identifying and localizing an obstructing bronchial lesion. Correlation with a chest radiograph helps in the evaluation, as does careful examination of the mediastinum, hilum, and pleura.
The primary changes of lobar collapse on CT scan are as follows:
- Irregular narrowing or occlusion of a bronchus indicates an obstructive lobar collapse.
- A lobe becomes pie shaped rather than hemispherical on cross-section.
- The lobe may be projected as a V-shaped structure where the apex is situated at the origin of the affected bronchus.
- The opacity of the lobe is increased overall.
- A mass may produce a bulge in the adjacent fissure (ie, the Golden sign of S).
- Previous pleural adhesions and fluid or air in the pleural space affect the pattern of collapse.
- The entire lobe may be infiltrated by the tumor, which gives it a lobular rather than wedge-shaped appearance.
RUL collapse
The RUL is bordered medially by the mediastinum, superiorly by the chest wall, inferiorly by the minor fissure, and posteroinferiorly by the superior portion of the oblique fissure.
On CT scanning, RUL collapse appears as a right paratracheal opacity, and the minor fissure appears concave laterally. The RUL collapses against the mediastinum, and this is identified as a wedge of uniform attenuation extending along the mediastinum to the anterior chest wall. Concomitant hyperinflation of the middle and lower lobes is present. A bulge in the contour of the collapsed RUL occurs secondary to an endobronchial tumor and gives an S-shaped configuration. Endobronchial obstruction is readily identifiable on the CT scan (see Image 18).
RML collapse
The RML is bounded medially by the right heart border; anteriorly and laterally by the chest wall; posteriorly by the major fissure; and superiorly, the minor fissure.
As the RML collapses, the minor fissure shifts downward and the oblique fissure is displaced forward. With a progressive loss of volume, the middle lobe collapses medially against the right heart border. The collapsed middle lobe is a wedge-shaped opacity that extends laterally from the hilum toward the lateral chest wall. It is bounded posteriorly by the RLL and anteriorly by the hyperinflated RUL.
On CT scans, a triangular opacity along the right heart border, with the apex pointing laterally, is a characteristic finding. This appearance resembles a tilted ice-cream cone.
RLL collapse
The RLL is bordered inferiorly by the hemidiaphragm, posteriorly and laterally by the chest wall, medially by the heart and mediastinum, and anteriorly by the major fissure.
The RLL generally collapses in a posteromedial direction against the posterior mediastinum and spine. An endobronchial lesion may result in a convex lateral contour of the collapsed RLL. The major fissure is displaced posteromedially.
LUL collapse
The LUL is bounded medially by the mediastinum, inferiorly by the left heart border, superiorly and laterally by the chest wall, and posteriorly by the major fissure.
CT scanning shows the inferior location of the collapsed lobe and the shift of the RUL across the midline. LUL collapse occurs anterosuperiorly. As opposed to the RUL, the collapsed LUL maintains more contact with the anterior and lateral chest wall. Hyperaeration of the superior segment of the LLL may cause displacement and superior movement; these changes may account for periaortic lucency or the luftsichel sign on PA images. The LUL maintains its contact with the mediastinum and remains attached to the left hilum by a wedge of collapsed tissue. The anterosuperior direction of the collapse projects a wedge-shaped triangular opacity, with the apex pointing posteriorly. Endobronchial obstruction is easily identified on CT scans.
LLL collapse
The LLL is bordered inferiorly by the hemidiaphragm, posteriorly and laterally by the chest wall, medially by the heart and mediastinum, and anteriorly by the major fissure. The LLL collapses medially toward the mediastinum and maintains contact with the hemidiaphragms. The major fissure moves posteriorly. The LLL has an opacity situated against the posterior mediastinum. CT scanning shows the atelectatic LLL in the inferior posterior location (see Image 12).
Passive atelectasis
Passive atelectasis is likely the most common form of atelectasis. It occurs secondary to the presence of air or fluid in the pleural space. The CT scan easily depicts pleural effusion and the underlying collapsed lung. Differentiation may be made easier with the use of contrast medium. The pattern of collapse secondary to an endobronchial lesion is distorted in the presence of pleural fluid. CT scanning may be of some help in distinguishing benign causes from malignant causes of pleural effusion. An irregular or nodular pleural surface may indicate an underlying malignancy.
Cicatrization atelectasis
Scarring or fibrosis from an inflammatory disease may lead to cicatrization collapse, the most common example being previous tuberculosis.
In cicatrization atelectasis, an endobronchial lesion is not seen and the bronchial tree in the collapsed lobe is hidden. Marked volume loss is present, and bronchiectatic changes frequently occur in the involved lobe.
Chronic middle-lobe syndrome results in a patent bronchus. Significant bronchiectasis and scarring may be observed in the collapsed lobe.
Adhesive atelectasis
Adhesive atelectasis occurs secondary to the loss of surfactant. A common cause is lung collapse due to radiation pneumonitis. The CT scan appearance is a sharp line demarcating the normal pulmonary parenchyma from the irradiated lung, which is generally paramediastinal.
Replacement atelectasis
Replacement atelectasis is a form of volume loss in which the pulmonary parenchyma is replaced by tumor infiltration. In this situation, the CT scan shows uniform attenuation throughout the involved lobe. This finding generally mimics consolidation. The tumor may grow into the edges and structures, such as the chest wall or mediastinum.
Rounded atelectasis
Rounded atelectasis is a form of chronic atelectasis that may appear as a mass lesion on chest radiographs. Although this form is most commonly associated with asbestos exposure, other benign conditions may also be present. These conditions include tuberculosis, uremic pleuritis, pulmonary infarction, and other causes of pleuritis. Because of adhesions between the visceral pleura and parietal pleura, the atelectatic lung becomes trapped and folds onto itself.
In cases of rounded atelectasis, the CT scan results are diagnostic and definitive; therefore, further investigations to exclude lung cancer are not required.. The CT scan findings are a peripheral oval or wedge-shaped attenuating area with smooth lateral edges and a medial irregular or ill-defined border that points to the hilum. Distortion and displacement of the blood vessels and bronchi appear in a characteristic curvilinear configuration that leads to the rounded atelectasis (ie, comet-tail sign). In most cases, bronchograms are seen on the CT scan, and calcification is also common.
Degree of Confidence
The common etiologies of lobar collapse include central endobronchial tumor, long-standing infection, pleural disease, and previous irradiation. CT scanning may play an important role in differentiating obstructive endobronchial lesions from other forms of collapse. By identifying the exact location of an endobronchial lesion and the presence of peribronchial spread, CT scans may be helpful in planning bronchoscopy and transbronchial biopsy. Evaluation of the mediastinum, pleura, chest wall, and adrenal glands plays a role in the staging process.
In evaluating patients with radiographically atypical forms of collapse, CT scans further help in accurately delineating the collapse and in identifying any additional pathology.16,17 CT scans are particularly helpful in patients who have a pleural effusion associated with atelectasis, and these images have a significant advantage over plain radiographs in the assessment of pleural malignancy. Finally, CT scans are especially useful in evaluating patients with cicatrization atelectasis. These patients have underlying bronchiectasis and present with atypical plain radiographic findings.
False Positives/Negatives
Determining the cause of an endobronchial obstruction on the basis of CT scans alone may be difficult. CT scans may not be useful in distinguishing among an endobronchial malignancy, a benign tumor, mucus plug, blood clot, and another nonopaque foreign body. Significant lung collapse associated with pleural effusion may not have the characteristic findings of lobar collapse; therefore, discerning whether an endobronchial lesion is present may be difficult.
CT scans may not be accurate in identifying benign and malignant causes of pleural effusion. CT scanning is also limited in differentiating a consolidation secondary to an infectious cause from a replacement collapse in which a tumor has infiltrated the entire lobe.
CT scans do not obviate bronchoscopy, which is a mandatory procedure to accurately localize an endobronchial lesion and to characterize its nature. Bronchoscopy may also serve a therapeutic role.
Magnetic Resonance Imaging
Findings
The role of MRI in differentiating a central obstructing tumor from a peripheral collapsed lung has been evaluated. T2-weighted sequences are useful in identifying an endobronchial lesion.13 Because lipid-laden macrophages accumulate in the subacute phase of lobar collapse, progressive lymphocytic infiltration and collagen deposition occur within the pulmonary interstitium. In these situations in which the ratio of lung to fat in the collapsed lung is greater than 1, T2-weighted MRIs are most useful in differentiating a tumor from lung collapse.
MRI may have a role in the evaluation of adhesive atelectasis. T2-weighted sequences may help in differentiating fibrosis secondary to an endobronchial obstruction from radiation-induced pneumonitis. Furthermore, MRI may have a role in diagnosing rounded atelectasis because MRIs may more accurately depict curvilinear vessels in the folded lung.
Degree of Confidence
MRI is an excellent imaging modality in situations in which intravenous contrast material cannot be administered. MRIs may delineate the extent and the location of a tumor; this modality may also have a role when CT scans are not helpful in differentiating between a tumor and a collapsed lung.
False Positives/Negatives
In a study of 10 patients, MRI was useful in identifying a tumor due to a collapsed lung in 5 (50%) patients, as compared with CT scanning. In the same study, CT scanning successfully differentiated between tumor and lung collapse in 8 (80%) of 10 patients. Interestingly, MRI was successful in 2 cases in which differentiation was not possible with CT scanning.
Ultrasonography
Findings
Ultrasonography has a limited role in the evaluation of atelectasis. The only potential role for this modality is in differentiating a basal lung collapse from a loculated pleural effusion. However, there are data to support the use of bedside ultrasonography in cases in which the clinical history and findings as well as the radiologic studies of critically ill patients are inconclusive.18,19
Degree of Confidence
CT scanning is preferred to ultrasonography because CT scanning is more accurate, delineates the surrounding structures better, and is also more useful in identifying the cause of atelectasis.
More on Atelectasis, Lobar |
| Overview: Atelectasis, Lobar |
 Imaging: Atelectasis, Lobar |
| Follow-up: Atelectasis, Lobar |
| Multimedia: Atelectasis, Lobar |
| References |
| « Previous Page | Next Page » |
References
Qureshi NR, Gleeson FV. Imaging of pleural disease. Clin Chest Med. Jun 2006;27(2):193-213. [Medline].
Ashizawa K, Hayashi K, Aso N, Minami K. Lobar atelectasis: diagnostic pitfalls on chest radiography. Br J Radiol. Jan 2001;74(877):89-97. [Medline]. [Full Text].
Woodring JH, Reed JC. Radiographic manifestations of lobar atelectasis. J Thorac Imaging. 1996;11(2):109-44. [Medline]. [Full Text].
Stark P, Leung A. Effects of lobar atelectasis on the distribution of pleural effusion and pneumothorax. J Thorac Imaging. 1996;11(2):145-9. [Medline].
Proto AV, Tocino I. Radiographic manifestations of lobar collapse. Semin Roentgenol. Apr 1980;15(2):117-73. [Medline].
McHugh K, Blaquiere RM. CT features of rounded atelectasis. AJR Am J Roentgenol. Aug 1989;153(2):257-60. [Medline]. [Full Text].
Westcott JL, Cole S. Plate atelectasis. Radiology. Apr 1985;155(1):1-9. [Medline]. [Full Text].
Molina PL, Hiken JN, Glazer HS. Imaging evaluation of obstructive atelectasis. J Thorac Imaging. 1996;11(3):176-86. [Medline].
Lee KS, Logan PM, Primack SL, Müller NL. Combined lobar atelectasis of the right lung: imaging findings. AJR Am J Roentgenol. Jul 1994;163(1):43-7. [Medline]. [Full Text].
Woodring JH. Determining the cause of pulmonary atelectasis: a comparison of plain radiography and CT. AJR Am J Roentgenol. Apr 1988;150(4):757-63. [Medline]. [Full Text].
Khoury MB, Godwin JD, Halvorsen RA Jr, Putman CE. CT of obstructive lobar collapse. Invest Radiol. Oct 1985;20(7):708-16. [Medline].
Naidich DP, McCauley DI, Khouri NF, et al. Computed tomography of lobar collapse: 1. Endobronchial obstruction. J Comput Assist Tomogr. Oct 1983;7(5):745-57. [Medline].
Herold CJ, Kuhlman JE, Zerhouni EA. Pulmonary atelectasis: signal patterns with MR imaging. Radiology. Mar 1991;178(3):715-20. [Medline]. [Full Text].
Kattan KR, Eyler WR, Felson B. The juxtaphrenic peak in upper lobe collapse. Semin Roentgenol. Apr 1980;15(2):187-93. [Medline].
Partap VA. The comet tail sign. Radiology. Nov 1999;213(2):553-4. [Medline]. [Full Text].
Gurney JW. Atypical manifestations of pulmonary atelectasis. J Thorac Imaging. 1996;11(3):165-75. [Medline].
Franken EA Jr, Klatte EC. Atypical (peripheral) upper lobe collapse. Ann Radiol (Paris). Jan-Feb 1977;20(1):87-93. [Medline].
Alptekin B, Tran DT, Lisbon A, Kaynar AM. Bedside ultrasonography in the differential diagnosis of pulmonary pathologies in the intensive care unit. J Clin Anesth. Nov 2006;18(7):534-6. [Medline].
Volpicelli G, Mussa A, Garofalo G, et al. Bedside lung ultrasound in the assessment of alveolar-interstitial syndrome. Am J Emerg Med. Oct 2006;24(6):689-96. [Medline].
Wu KH, Lin CF, Huang CJ, Chen CC. Rigid ventilation bronchoscopy under general anesthesia for treatment of pediatric pulmonary atelectasis caused by pneumonia: a review of 33 cases. Int Surg. Sep-Oct 2006;91(5):291-4. [Medline].
Cai H, Gong H, Zhang L, Wang Y, Tian Y. Effect of low tidal volume ventilation on atelectasis in patients during general anesthesia: a computed tomographic scan. J Clin Anesth. Mar 2007;19(2):125-9. [Medline].
Mahmut M, Nishitani H. Evaluation of pulmonary lobe variations using multidetector row computed tomography. J Comput Assist Tomogr. Nov-Dec 2007;31(6):956-60. [Medline].
Proto AV. Lobar collapse: basic concepts. Eur J Radiol. Aug 1996;23(1):9-22. [Medline].
Stark P. Round atelectasis: another pulmonary pseudotumor. Am Rev Respir Dis. Feb 1982;125(2):248-50. [Medline].
Toyoshima M, Maeoka Y, Kawahara H, Maegaki Y, Ohno K. [Pulmonary atelectasis in patients with neurological or muscular disease; gravity-related lung compression by the heart and intra-abdominal organs on persistent supine position] [Japanese]. No To Hattatsu. Nov 2006;38(6):419-24. [Medline].
Further Reading
Keywords
obstructive atelectasis, nonobstructive atelectasis, platelike atelectasis, discoid atelectasis, subsegmental atelectasis postoperative atelectasis, cicatrization atelectasis, rounded atelectasis, folded-lung syndrome, Blesovsky syndrome, Blesovsky's syndrome, replacement atelectasis, incomplete expansion, diminished lung volume, pulmonary volume deficiency, lung foreign body, lung tumor, mucus plugging, pleural effusion, right middle lobe syndrome, atelectatic lung tissue, bronchial obstruction, pneumothorax lobar collapse, pneumothorax, airless lung
