pleural synovial sarcoma
Tuesday 13 September 2011
Definition: Primary pleural synovial sarcomas are very rare, more commonly representing a metastasis from a soft tissue primary site.
They can present with chest pain, dyspnoea, cough84 or pleural effusion, all typical symptoms of malignant mesothelioma.
However, they typically occur in a younger age group, the average age at diagnosis being 33 years, and they most commonly grow as a localized mass.
Histologically, they may have a monophasic or biphasic growth pattern, the latter being more common in the pleura.
Synovial sarcoma tends to be more densely cellular than sarcomatoid mesothelioma, with long fascicles of spindle cells usually displaying only a mild degree of pleomorphism, whereas mesothelioma typically shows short fascicles of less crowded spindle cells with more significant pleomorphism.
The epithelial component, if present, can be subtle and become evident only when highlighted by immunohistochemistry, or it may be more obvious, with gland formation.
Immunohistochemistry is useful in distinguishing synovial sarcoma from malignant mesothelioma.
CK immunoreactivity is generally diffusely positive in malignant mesothelioma but only focally positive in synovial sarcoma.
Synovial sarcoma is typically positive for Bcl-2, whereas malignant mesothelioma is only occasionally positive.
It should be noted that synovial sarcoma can be positive for calretinin and that CD99, often used in the diagnosis of synovial sarcoma, is positive in approximately half of all malignant mesotheliomas.
The diagnosis of synovial sarcoma can be confirmed by demonstration of the chromosomal translocation t(X;18).