DOI: 10.1148/radiol.2431041658
(Radiology 2007;243:297-298.)
© RSNA, 2007
The Split Pleura Sign1
Guenther J. Kraus, MD
1 From the Department of Radiology, General Hospital Graz-West, Graz, Austria. Received September 30, 2004; revision requested December 2, 2004; revision received December 10, 2004; final version accepted January 17, 2005.
Address correspondence to the author, Diagnoztikzentrum Urania, Laurenzerberg 2, 1010 Vienna, Austria (e-mail: krausgj{at}hotmail.com).
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APPEARANCE
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The split pleura sign is seen on contrast material–enhanced chest computed tomographic (CT) images. There is enhancement of the thickened inner visceral and outer parietal pleura, with separation by a collection of pleural fluid (Figure) (1).
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EXPLANATION
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Thoracic empyema is defined as purulent content in the pleural cavity (1).
Empyema most commonly occurs in the setting of bacterial pneumonia. It typically develops from transformation of a parapneumonic effusion (not infected) into a complicated effusion (features of infection but not purulent) and then into empyema (frank pus) (2,3).
In parapneumonic effusion, fluid moves in the interpleural space due to increased capillary vascular permeability. Proinflammatory cytokines facilitate the fluid entry into the pleural cavity and cause hyperemia. With increasing fluid accumulation and bacterial invasion through the damaged endothelium, transudative effusion progresses to empyema (3). As empyema progresses, a fibrin peel coats the surfaces of the visceral and parietal pleural layers with ingrowth of capillaries and fibroblasts and subsequent thickening. This forms the basis of the split pleura sign: thickened visceral and parietal pleural layers separated by empyema (1).
The fibrin peel can organize as early as 7 days after the onset of the disease (4).
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DISCUSSION
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In one major study (1), pleural separation ("split pleura") was seen in 68% (39 of 57) of empyema patients. In another study (5), patients with empyema showed enhancement of the pleura in 86% (30 of 35) of all cases, predominantly of the parietal pleura. Thickening and enhancement can be seen with exsudative effusions in 61% (36 of 59), but not with transudative effusions (5). Empyema is often accompanied by swelling of the extrapleural subcostal tissue (60%, 21 of 35), and increased attenuation of the extrapleural fat can appear (34%, 12 of 35) (6).
CT has been reported as having a high accuracy (100%, 70 of 70) in differentiating empyema from a lung abscess (1).
Pleural changes similar to those of empyema can be seen with malignant effusions (especially after talc pleurodesis), mesothelioma, and hemothorax and after lobectomy (2,7).
About half of empyemas are caused by Gram-positive bacteria (Staphylococcus aureus, Streptococcus pneumoniae); the remainder are Gram-negative organisms commonly growing together with other Gram-negative organisms or anaerobes (1,3).
In summary, the split pleura sign refers to thickening and increased contrast enhancement of the visceral and the parietal pleura separated by empyema or an exsudative effusion.
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FOOTNOTES
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Author stated no financial relationship to disclose.
| A trainee (resident or fellow) wishing to submit a manuscript for Signs in Imaging should first write to the Editor for approval of the sign to be prepared, to avoid duplicate preparation of the same sign.
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References
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- Stark DD, Federle MP, Goodman PC, Podrasky AE, Webb WR. Differentiating lung abscess and empyema: radiography and computed tomography. AJR Am J Roentgenol 1983;141:163–137.[Abstract/Free Full Text]
- Aquino SL, Webb WR, Gushiken BJ. Pleural exudates and transudates: diagnosis with contrast-enhanced CT. Radiology 1994;192:803–808.[Abstract/Free Full Text]
- Davies CW, Gleeson FV, Davies RJ; Pleural Diseases Group, Standards of Care Committee, British Thoracic Society. BTS guidelines for the management of pleural infection. Thorax 2003;58(suppl 2):ii18–ii28.[Free Full Text]
- Alexander JC, Wolfe WG. Lung abscess and empyema of the thorax. Surg Clin North Am 1980;60:835–849.[Medline]
- Waite RJ, Carbonneau RJ, Balikian JP, et al. Parietal pleural changes in empyema: appearances at CT. Radiology 1990;175:145–150.[Abstract/Free Full Text]
- Takasugi JE, Godwin JD, Teefey SA. The extrapleural fat in empyema: CT appearance. Br J Radiol 1991;64:580–583.[Abstract/Free Full Text]
- Collins J. CT signs and patterns of lung disease. Radiol Clin North Am 2001;39:1115–1135.[CrossRef][Medline]
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