British Journal of Radiology (2005) 78, 858-861
© 2005 British Institute of Radiology
doi: 10.1259/bjr/19513813
Incidental localized (solitary) mediastinal malignant mesothelioma
E Erdogan, MD1,
F B Demirkaz
k, MD1,
M Gulsun, MD1,
M Aryurek, MD1,
S Emri, MD2 and
S D Sak, MD3
Departments of 1 Radiology and 2 Chest Diseases, Hacettepe University School of Medicine, 06100 Ankara, Turkey and 3 Department of Pathology, Ankara University, Ankara, Turkey
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Abstract
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Primary mediastinal mesotheliomas are rare tumours. The mesothelial lining cells of the the pericardium are suggested as the most probable cells of origin. Most of these tumours appear either as a diffuse or nodular thickening of the pericardium that encase and even invade the heart. Localized mediastinal mesotheliomas are distinctly uncommon. We report the imaging findings of a solitary malignant mediastinal mesothelioma that presented mainly as a cystic anterior mediastinal mass. On chest radiography, the tumour appeared as a right paramediastinal soft tissue mass located adjacent to the right middle and lower lobes. On CT, a large, well-circumscribed, right anterior mediastinal mass with a central zone of fluid attenuation was observed. This mass had a thin, smooth wall of uniform thickness as well as a small component that demonstrated soft tissue attenuation. There was no plane of separation between the tumour and aorta/superior vena cava. At surgery the tumour could be dissected easily free from the pericardium and great vessels and it was removed totally. Histopathological examination of the tumour revealed a malignant epitheloid mesothelioma.
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Introduction
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Localized mesothelioma of the mediastinum is a very rare condition with little published on imaging features. Most of the cases reported in previous literature were diffusely infiltrating pericardial mesothelioma cases. Only a few number of cases of localized malignant pericardial mesothelioma have been reported so far [1]. We present the imaging findings of this very rare occurrence.
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Case report
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A 74-year-old male was admitted to our hospital for the evaluation of loss of appetite, fatigue and generalized bone pain. He also had a weight loss of 5 kg in the past 3 months. His past medical history was uneventful except for coronary bypass surgery and gout.
The patient had smoked for 6 years about 40 years ago and had not smoked since. He was a retired internist and gave a negative history for both environmental and occupational asbestos exposure. His physical examination was unremarkable except for the decreased breath sounds by auscultation and dullness by percussion at the lower half of the right lung. The laboratory findings were normal except for markedly elevated erythrocyte sedimentation rate (120 mm h–1), blood urea nitrogen (37 mg dl–1), and anaemia (haemoglobin: 9 g dl–1). Posteranterior (PA) chest radiograph showed a lobulated paramediastinal soft tissue density in the right mid and lower chest (Figure 1
). Contrast enhanced thorax CT showed a 6 cm x 5 cm x 4 cm right anterior mediastinal mass with a predominant cystic appearing component (Figure 2a,b). A smooth, well-defined wall of uniform thickness surrounded the cystic appearing component. The mass also had a soft tissue component that was in close relation with the ascending aorta. There was no plane of separation between the tumour and aorta. The tumour was located besides the right atrial appendage and superior vena cava but there were no signs of invasion to these structures on CT. There was focal thickening of the pericardium adjacent to the mass, suggesting that the mass might have originated from the pericardium (Figure 2c). There was no accompanying pleural or pericardial effusion. The left hemithorax was completely normal. The tumour could be freed and dissected from the pericardium and other mediastinal structures and could be removed totally. Histological examination revealed atypical epithelial cells with vesicular nuclei and prominent nucleoli forming papillary and glandular structures and sheets (Figure 3a). Using immunohistochemistry, the tumour cells showed strong cytoplasmic positivity for pancytokeratin and vimentin. The epithelial membrane antigen yielded positive staining of the cell membranes. Mesothelin staining of the tumour showed membranous staining with apical accentuation (Figure 3b,c). With the above mentioned histopathological and immunohistochemical findings, the tumour was diagnosed as malignant epitheloid mesothelioma in spite of the unusual clinical findings. The post-operative period was uneventful. However, follow up CT after 3 months showed recurrent mass at the same site (Figure 4a,b). This mass was mainly of soft tissue attenuation without a remarkable cystic component. Contrast enhanced MRI (Figure 4c–e) showed that the mass was hyperintense on both T1 and T2 weighted sequences. Diffuse and homogeneous contrast enhancement of the mass was noted. CT-guided transthoracic biopsy confirmed the diagnosis of recurrent malignant epitheloid mesothelioma. The patient was not given any treatment for the recurrent tumour. Follow-up chest radiographs showed that the tumour size continued to increase gradually, however the tumour remained localized.
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Figure 1. A lobulated paramediastinal soft tissue density in the right mid and lower chest was observed on chest radiography.
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Figure 2. (a) Contrast enhanced thorax CT showed a 6 cm x 5 cm x 4 cm mass with a predominant cystic component The cyst was surrounded by a smooth, well defined wall of uniform thickness. (b) A solid component of soft tissue attenuation with borders that were not separable from the ascending aorta was also observed. (c) At the level of left atrium, the mass appears to have no solid component at all.
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Figure 3. (a) Haematoxylin and eosin staining of the tumour revealed atypical epithelial cells with vesicular nuclei and prominent nucleoli forming papillary and glandular structures and sheets. (b, c) Mesothelin staining of the tumour showing membraneous staining with apical accentuation.
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Figure 4. (a, b) CT obtained 3 months after total tumour excision shows a smaller contrast enhancing mass of soft tissue attenuation without remarkable cystic component at the same location as the original tumour. Biopsy from this mass revealed tumour recurrence. (c) Post contrast T1 weighted, (b) T2 weighted axial, and (e) pre-contrast T1 weighted sagittal images obtained within few days as the CT in (a, b) demonstrate the recurrent contrast enhancing anterior mediastinal tumour.
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Discussion
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Malignant mediastinal mesotheliomas are rare tumours. They are considered to arise mainly from the mesothelial cells of the pericardium. Thus, cases have been reported in the literature mainly as "pericardial mesothelioma". Pericardial mesotheliomas comprise less than 5% of all mesotheliomas [2]. They present either as an encasing mass involving the whole pericardium [3], or less frequently as a localized tumour associated with pericardial effusion [4]. Occasionally, invasion of the cardiac chambers and even more rarely distant metastasis of pericardial mesotheliomas have been reported [5, 6]. Localized pericardial mesothelioma is considered as a rare variant of malignant mesothelioma. Only a few number of cases have been reported so far in the English literature [1, 7–9].
Pericardial mesotheliomas are usually difficult to diagnose unless they cause haemodynamic disturbances due to cardiac encasement and/or invasion. The insidious onset of symptoms of pericardial mesotheliomas may mimic symptoms secondary to benign pericardial constriction. Localized cases and cases with mild pericardial involvement are usually diagnosed incidentally while the patient is evaluated for another reason. On the other hand, advanced cases can present with haemodynamic disturbances suggesting pericardial tamponade or constrictive pericarditis. In the present case, the patient did not have a respiratory or haemodynamic disturbance and the mass was found incidentally on chest radiography.
Pericardial mesotheliomas may present as an enlarged cardiac silhouette with or without accompanying pleural effusion on chest radiography. Sometimes a mediastinal mass adjacent to the heart can be the only finding, as it is the case of our patient. CT and echocardiography can show the abnormally thickened pericardium encasing the heart. Usually, pericardial, and sometimes pleural, effusion accompanies the thickened pericardium. In our case, there was no diffuse pericardial thickening and pleural or pericardial effusion. The mass in our case was mainly cystic in appearance with relatively smaller soft tissue component, located on the right side of the anterior mediastinum.
The mainly cystic appearance of the initial tumour on CT in this case together with the histopathological diagnosis of mesothelioma led us to consider that the tumour might be cystic malignant mesothelioma, but histopathological examination of the tumour revealed solid cords of epitheloid mesothelial cells without any cystic areas. This indicated that the tumour was an epitheloid type malignant mesothelioma, not a malignant cystic mesothelioma. The latter is characterized histopathologically by multilocular cystic cavities whose walls are lined by huge numbers of atypical mesothelial cells [2]. With all these radiological and histopathological findings we concluded that the tumour was a localized malignant mediastinal mesothelioma and the pericardium was the most probable site of origin There is one case report of a malignant epithelial mesothelioma that presented as an anterior mediastinal mass of soft tissue density similar to our case; however, the possible site of origin for this lesion has not been mentioned [10]. The appearance of the large round cystic mass with a smooth, well-defined, intensely enhancing wall cannot be precisely explained, but tumour necrosis at the centre of this large mass seems to be the most likely explanation.
The radiological differential diagnosis of localized malignant mesothelioma of the pericardium includes solitary fibrous tumour of the pericardium [11], synovial sarcoma of the heart and pericardium [12, 13], epitheloid angiosarcoma [14] and adenomatoid tumour [15]. Since the initial tumour in our case had a cystic component on CT, cystic thymoma and pericardial cysts should be considered in the differential diagnosis. Imaging findings are generally not helpful for differential diagnosis and these tumours can only be differentiated by histopathological examination.
Because of the lack of specific symptoms, these tumours are usually detected late in the course of the disease. The tumour in the present case recurred shortly after total excision. The recurrent mass was a mainly solid mass of soft tissue attenuation without a remarkable cystic component.
In conclusion, we demonstrated a very unusual, mainly cystic localized mediastinal mesothelioma, which might have originated from the pericardium. The atypical presentation of this very rare tumour should be considered in the differential diagnosis of a cystic mediastinal mass.
Received for publication November 4, 2004.
Revision received March 29, 2005.
Accepted for publication April 14, 2005.
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References
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Abstract
Introduction
