A biphasic tumor of the mediastinum with features of synovial sarcoma. A report of four cases

Our plain-English summary of A biphasic tumor of the mediastinum with features of synovial sarcoma. A report of four cases, by G.B. Witkin, M. Miettinen, J. Rosai (The American Journal of Surgical Pathology, 1989).

The study

• Authors: G.B. Witkin, M. Miettinen, J. Rosai
• Journal: The American Journal of Surgical Pathology
• Published: 1989;13(6):490-9
• Cited by: 80 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

Four cases of a biphasic mediastinal tumor histologically identical to synovial sarcoma of soft tissue were observed. The tumors presented as solitary mediastinal masses. Although the tumors were frequently adherent to adjacent pleura or pericardium, none appeared to be arising from a mesothelial surface. All cases were composed of an intimate admixture of keratin-positive epithelial cells and vimentin-positive spindle cells with areas of transition, hyalinization, and calcification. Follow-up was available on three patients, who died of their disease 10 months, 14 months, and 4 years after diagnosis, respectively. Although synovial sarcoma usually occurs in deep soft tissues near joints in the extremities, it has been reported in locations removed from synovial, tendon sheath, and bursal structures. This report adds a previously unrecognized location for synovial sarcoma, the mediastinum. Occurrence in this location further supports an origin from pluripotential mesenchyme as opposed to synovium. The differential diagnosis includes mesothelioma, thymoma, germ cell tumors, malignant peripheral nerve sheath tumor with glandular differentiation, and metastatic carcinoma.

In plain English

This case series described four tumors of the mediastinum, the space in the middle of the chest. Under the microscope they resembled synovial sarcoma, a cancer usually found near joints of the limbs. Three cases came from one author's consultation files and one from the University of Helsinki. All four patients were adult men aged 40 to 73. No case had a reported history of asbestos exposure. The tumors measured 5 to 12 cm. All contained a mix of keratin-positive epithelial cells and vimentin-positive spindle cells. Some tumors were stuck to the pleura or pericardium, but none appeared to arise from a mesothelial surface. The three patients with follow-up died of the disease 10 months to 4 years after diagnosis. The authors wrote that telling a localized biphasic mesothelioma with a synovial sarcoma-like pattern apart from synovial sarcoma may be impossible. For a solitary mass without clear evidence of mesothelial origin and a pattern identical to synovial sarcoma, they favored synovial sarcoma. The authors concluded that this site supports an origin from pluripotential mesenchyme, not synovium.

We wrote this plain-English summary from the full article with the help of AI, and a second AI model checked each sentence against the article. It is not the authors' wording; the abstract and the article are their own account.

What the study did and found

• Design: case series (report of four cases), pathology study of tissue slides, special stains and immunostaining
• Who was studied: Four adult men, aged 40, 46, 47 and 73, each with a single mediastinal mass. Three cases came from the consultation files of one author (J.R., Yale) and one from the files of the University of Helsinki. Dates of diagnosis are not given.
• Exposure: Asbestos was not the subject of the study. The authors report that no case had a reported history of asbestos exposure.
• Main results:
  • The tumors ranged in size from 5 to 12 cm.
  • All four cases showed keratin staining in the epithelial component. Vimentin staining, limited to the spindle cell component, was seen in all cases, but the recurrent tumor in case 2 was negative for vimentin.
  • Apart from sticking to the pleura or pericardium, and invading the lung in case 1, none of the tumors appeared to arise from a mesothelial surface.
  • All three patients with follow-up died 10 months to 4 years after diagnosis. Follow-up was not available for case 4.
  • The authors considered mesothelioma the hardest diagnosis to exclude. For a solitary mass without clear evidence of mesothelial origin and an appearance identical to synovial sarcoma, they favored synovial sarcoma.
• The authors' conclusion: The authors concluded that the occurrence of synovial sarcoma in the mediastinum, another site removed from synovial structures, supports an origin from pluripotential mesenchyme rather than from synovium.
• Limitations the authors state:
  • The authors state that telling a localized biphasic mesothelioma with a synovial sarcoma-like pattern apart from synovial sarcoma may be impossible.
  • Electron microscopy was available only for the recurrent tumor in case 2.
  • No autopsies were performed in any case.

Topics

Medical terms in this study, explained in our Lexicon: Biphasic Mesothelioma, Mediastinum, Synovial Sarcoma, Pleura, Pericardium, Spindle Cell, Differential Diagnosis, Mesothelioma.

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• Solitary fibrous tumor of the mediastinum — N. Weidner (1991)
• Solitary fibrous tumor of the mediastinum. A report of 14 cases — G.B. Witkin, J. Rosai (1989)
• Synovial sarcoma of the pleura and its differentiation from other primary pleural tumours: a clinicopathological and immunohistochemical review of three cases — A.G. Nicholson, P. Goldstraw, et al. (1998)
• Challenges and controversies in the diagnosis of malignant mesothelioma: Part 2. Malignant mesothelioma subtypes, pleural synovial sarcoma, molecular and prognostic aspects of mesothelioma, BAP1, aquaporin-1 and microRNA — D.W. Henderson, G. Reid, et al. (2013)

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