(Radiology. 2000;216:478-480.)
© RSNA, 2000
Pseudochylous Pleural Effusion with Fat-Fluid Levels: Report of Six Cases1
Jae-Woo Song, MD,
Jung-Gi Im, MD,
Jin Mo Goo, MD,
Hyae Young Kim, MD,
Chi Sung Song, MD and
Jeong Sang Lee, MD
1 From the Departments of Radiology (J.W.S., C.S.S.) and Thoracic Surgery (J.S.L.), Seoul Municipal Boramae Hospital Affiliated to Seoul National University Hospital, #395 Shindaebang-dong, Tongjak-ku, Seoul 156-012, Korea; the Department of Radiology, Seoul National University College of Medicine (J.G.I., J.M.G.); and the Department of Radiology, Ewha Woman's University Mokdong Hospital, Seoul, Korea (H.Y.K.). Received May 3, 1999; revision requested July 14; revision received November 17; accepted December 7. Address correspondence to J.W.S. (e-mail: jwsong@medikorea.net).
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ABSTRACT
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The authors report the clinical and computed tomographic (CT) findings in six patients with chyliform pleural effusion. All six patients had a medical history of pleurisy before presentation; five of them had tuberculous pleural effusion. The CT scans of all six patients showed variable amounts of pleural fluid collection with a layering of fat at the nondependent site.
Index terms: Pleura, fluid, 60.234 • Thorax, CT, 60.12112 • Thorax, diseases, 60.234 • Tuberculosis, 60.234
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INTRODUCTION
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Chyliform pleural effusion, often called pseudochylous or cholesterol effusion, is a high-lipid effusion that is not chylous (1). The chyliform pleural effusion is formed on the basis of a chronic pleural effusion surrounded by thickened and fibrotic pleurae (2). The most common cause of this pleural reaction is tuberculous pleurisy, but it has also been described in association with rheumatoid arthritis (1–3). The presence of a fat-fluid level within the pleural space is unique to pseudochylous effusion. However, to the best of our knowledge, there has been no previous report in which the presence of a fat-fluid level at computed tomography (CT) has been described. We report six cases of chyliform pleural effusion in six consecutive patients who presented with a loculated pleural fluid collection that contained a fat-fluid or fat-calcium level at CT.
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Case Reports
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Clinical Information
Six patients (four men, two women; mean age, 54.3 years; age range, 37–74 years) who had a loculated pleural fluid collection that contained a fat-fluid or fat-calcium level at CT were included in this study. All six patients had a medical history of pleurisy—of 17–33 years before presentation in four patients and for an unknown period in two patients. Five patients had tuberculous pleural effusion and one had pleuropulmonary paragonimiasis. All five patients with tuberculous effusion had clinical symptoms related to the pleural lesions: dyspnea in one patient and chest pain or discomfort in four. The patient who had paragonimiasis did not have any clinical symptoms. The clinical histories of the six patients are summarized in Table 1.
Decortication (n = 2) or pleuropneumonectomy with decortication (n = 2) was performed in four of the five patients who had tuberculous effusion. Histopathologic examination of the surgical specimens from the empyemic cavity wall demonstrated chronic granulomatous inflammation with fibrosis and some foci of caseation necrosis. However, the stained and cultured surgical specimens were negative for microorganisms, including Mycobacterium species, in all four patients. In one patient (case 3) with tuberculous empyema, CT-guided aspiration of the fatty layer was performed. The aspirate was a thick, yellow, and clear fluid that looked like motor oil. We did not determine the chemical composition of this material, but it was evident that this was nonchylous lipid that had formed within the body.
CT Examinations
CT examinations were performed in the six patients in the supine position for the evaluation of masslike pleural lesions that were seen on chest radiographs by using a CT 9800 scanner (GE Medical Systems, Milwaukee, Wis) with contiguous 10-mm-thick sections after the bolus injection of 100 mL of contrast material (iopromide [Ultravist]; Schering, Berlin, Germany). In three patients, additional scans were obtained with the patients in the lateral decubitus position.
CT Findings
The CT scans of all six patients showed variable amounts of pleural fluid collection. A layering of fat at the nondependent site also was seen in all the patients: at the fat-fluid level in four patients (Fig 1) and at the fat-calcium level in two patients (Fig 2). The CT numbers of the fatty areas ranged from -90.0 to -115.0 HU (mean, -98.5 HU). The CT scans obtained in three patients in the lateral decubitus position showed the change at the fat-fluid or fat-calcium level along the line of gravity (Fig 1c). The parietal pleura encasing the pleural collection had thickened to 4–10 mm in five patients with tuberculous empyema and to 2 mm in the patient with pleuropulmonary paragonimiasis. There was nodular or curvilinear calcification in the wall of the empyemic sac in all five patients with tuberculous empyema. In three of four patients with a pleural fluid collection containing a fat-fluid level, the attenuation of the collection was heterogenous because of a varying amount of caseation material within the chronic tuberculous empyemic cavity. The major CT findings are summarized in Table 2.
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Figure 1a. Case 3. Images of the thorax in a 46-year-old woman with a history of tuberculous pleurisy for 33 years who presented with slowly progressive dyspnea. Histopathologic examination of the surgical specimen from the empyemic wall demonstrated chronic granulomatous inflammation with fibrosis and some foci of caseation necrosis. However, stained and cultured surgical and sputum specimens were negative for microorganisms, including Mycobacterium species. (a) Frontal chest radiograph shows nearly complete opacification of the right hemithorax, with a mediastinal shift to the contralateral hemithorax. (b) Contrast material-enhanced transverse CT scan shows diffuse pleural thickening with enhancement and multifocal calcifications in the wall of the empyemic cavity. Note the fat-fluid level (arrows) within the empyemic cavity. The CT number of the low-attenuating area is -90 HU, which is slightly lower than that of the subcutaneous fat (-75 HU). (c) Contrast-enhanced transverse CT scan obtained in the left lateral decubitus position shows shifting of the fat-fluid level (arrows), as expected.
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Figure 1b. Case 3. Images of the thorax in a 46-year-old woman with a history of tuberculous pleurisy for 33 years who presented with slowly progressive dyspnea. Histopathologic examination of the surgical specimen from the empyemic wall demonstrated chronic granulomatous inflammation with fibrosis and some foci of caseation necrosis. However, stained and cultured surgical and sputum specimens were negative for microorganisms, including Mycobacterium species. (a) Frontal chest radiograph shows nearly complete opacification of the right hemithorax, with a mediastinal shift to the contralateral hemithorax. (b) Contrast material-enhanced transverse CT scan shows diffuse pleural thickening with enhancement and multifocal calcifications in the wall of the empyemic cavity. Note the fat-fluid level (arrows) within the empyemic cavity. The CT number of the low-attenuating area is -90 HU, which is slightly lower than that of the subcutaneous fat (-75 HU). (c) Contrast-enhanced transverse CT scan obtained in the left lateral decubitus position shows shifting of the fat-fluid level (arrows), as expected.
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Figure 1c. Case 3. Images of the thorax in a 46-year-old woman with a history of tuberculous pleurisy for 33 years who presented with slowly progressive dyspnea. Histopathologic examination of the surgical specimen from the empyemic wall demonstrated chronic granulomatous inflammation with fibrosis and some foci of caseation necrosis. However, stained and cultured surgical and sputum specimens were negative for microorganisms, including Mycobacterium species. (a) Frontal chest radiograph shows nearly complete opacification of the right hemithorax, with a mediastinal shift to the contralateral hemithorax. (b) Contrast material-enhanced transverse CT scan shows diffuse pleural thickening with enhancement and multifocal calcifications in the wall of the empyemic cavity. Note the fat-fluid level (arrows) within the empyemic cavity. The CT number of the low-attenuating area is -90 HU, which is slightly lower than that of the subcutaneous fat (-75 HU). (c) Contrast-enhanced transverse CT scan obtained in the left lateral decubitus position shows shifting of the fat-fluid level (arrows), as expected.
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Figure 2a. Case 4. Images of the thorax in a 55-year-old woman with a history of tuberculous pleurisy and spondylitis for 30 years who presented with chest discomfort for 2 years. (a) Frontal chest radiograph shows homogeneous, increased opacification in the left lower hemithorax, which suggests pleural effusion. (b) Contrast-enhanced transverse CT scan obtained at the level of the diaphragmatic dome (window width, 400 HU; window level, 20 HU) shows a fat-calcium level (open arrow) in the left pleural space. The CT number of the low-attenuating area is -94 HU, and that of the high-attenuating area ranges from 164 to 273 HU. Note the volume loss in the left hemithorax and the accumulation of fat (solid arrows) in the extrapleural space, which indicates the long-standing nature of this process. (c) Contrast-enhanced transverse CT scan obtained at a different window and anatomic level (window width, 1,500 HU; window level, -50 HU) shows nodular and linear calcifications (arrows) in the thickened surrounding pleura.
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Figure 2b. Case 4. Images of the thorax in a 55-year-old woman with a history of tuberculous pleurisy and spondylitis for 30 years who presented with chest discomfort for 2 years. (a) Frontal chest radiograph shows homogeneous, increased opacification in the left lower hemithorax, which suggests pleural effusion. (b) Contrast-enhanced transverse CT scan obtained at the level of the diaphragmatic dome (window width, 400 HU; window level, 20 HU) shows a fat-calcium level (open arrow) in the left pleural space. The CT number of the low-attenuating area is -94 HU, and that of the high-attenuating area ranges from 164 to 273 HU. Note the volume loss in the left hemithorax and the accumulation of fat (solid arrows) in the extrapleural space, which indicates the long-standing nature of this process. (c) Contrast-enhanced transverse CT scan obtained at a different window and anatomic level (window width, 1,500 HU; window level, -50 HU) shows nodular and linear calcifications (arrows) in the thickened surrounding pleura.
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Figure 2c. Case 4. Images of the thorax in a 55-year-old woman with a history of tuberculous pleurisy and spondylitis for 30 years who presented with chest discomfort for 2 years. (a) Frontal chest radiograph shows homogeneous, increased opacification in the left lower hemithorax, which suggests pleural effusion. (b) Contrast-enhanced transverse CT scan obtained at the level of the diaphragmatic dome (window width, 400 HU; window level, 20 HU) shows a fat-calcium level (open arrow) in the left pleural space. The CT number of the low-attenuating area is -94 HU, and that of the high-attenuating area ranges from 164 to 273 HU. Note the volume loss in the left hemithorax and the accumulation of fat (solid arrows) in the extrapleural space, which indicates the long-standing nature of this process. (c) Contrast-enhanced transverse CT scan obtained at a different window and anatomic level (window width, 1,500 HU; window level, -50 HU) shows nodular and linear calcifications (arrows) in the thickened surrounding pleura.
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Discussion
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A chyliform pleural effusion, or pseudochyle, which was so named because it is not related to the disruption of the thoracic duct, is turbid or milky because of a high lipid content (1). In other words, all high-lipid nonchylous effusions can be called chyliform or pseudochylous pleural effusions. Pseudochylothoraces are much less common than chylothoraces. In a series of 53 nontraumatic, high-lipid effusions, only six (11%) were chyliform pleural effusions (1).
Chyliform pleural effusions have been recognized for more than a century. However, the precise pathogenesis of chyliform pleural effusions is unknown. The origin of the lipids in these effusions is thought to be degenerating red and white blood cells in the pleural fluid (4). The process is apparently initiated by pleurisy with thickened and sometimes calcified pleura. The diseased pleura may result in an abnormally slow transfer of cholesterol and other lipids out of the pleural space and lead to the accumulation of cholesterol in the pleural fluid (2,5). Tuberculosis is the most common disease associated with the onset of chronic pleurisy that eventually leads to chyliform effusion. Other reported underlying diseases include rheumatoid lung disease, alcoholism, syphilis, diabetes, Meigs syndrome, malignancy, paragonimiasis, and trauma or hemothorax (5).
The mean duration of pleural effusion before it turns chyliform is 5 years, but a few chyliform effusions have been known to develop within a year of onset (1). The radiographic features of chyliform effusion, with the exceptionof a loculated pleural collection or pleural thickening, which may be indicative of the long duration of the lesion, are nonspecific and not so different from those of chylous or other forms of pleural effusion. To our knowledge, the CT findings of chyliform effusion had not been reported before the present study.
In conclusion, the presence of a fat-fluid or fat-calcium level at CT is a unique finding of chyliform pleural effusion and is most commonly caused by tuberculous empyema.
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FOOTNOTES
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Author contributions: Guarantors of integrity of entire study, J.W.S., J.G.I., C.S.S.; study concepts; all authors; study design, J.W.S.; definition of intellectual content, all authors; literature research, J.W.S.; clinical studies, all authors; data acquisition, J.W.S., J.S.L.; data analysis, J.W.S., J.G.I., J.M.G., H.Y.K.; manuscript preparation, J.W.S.; manuscript editing, J.W.S., J.G.I.; manuscript review, all authors.
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Hamm H, Pfalzer B, Fabel H. Lipoprotein analysis in a chyliform pleural effusion: implications for pathogenesis and diagnosis. Respiration 1991; 58:294- 300.[Medline]
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ABSTRACT
INTRODUCTION
