Discussion
Synovial sarcomas are rare soft tissue malignancies mostly affecting the large joints of the extremities; other locations include the chest wall, mediastinum, pleura, or heart [1]. Pleural synovial sarcoma (PSS) is a subtype comprising only 0.1%-0.5% of primary lung malignancies [2].
PSSs typically occur in adolescents and adults between the ages of 15 and 40 years without sex predilection. Symptoms can include dyspnoea, chest pain, and cough. The histogenesis of PSS is uncertain, though they are hypothesised to arise from primitive pluripotent mesenchyme and can differentiate into spindle and/or epithelial cells [2, 3]. Many subtypes exist, including liposarcoma, chondrosarcoma, osteosarcoma, and malignant schwannoma [2]. PSS was only first described in literature in 2009. Detailed history, imaging, histology, immunochemistry, and cytogenetics are useful for accurate diagnosis. It is important to distinguish PSS from histologically similar spindle cell tumours since they are often mistaken for malignant mesothelioma [3], but PSS is aggressive with a high rate of recurrence [1].
PSS has sharp borders with round or lobulated contours [2]. On chest radiographs, PSS is homogenous, pleural-based soft-tissue mass, usually without calcifications, cavitation, or associated lymphadenopathy [4]. It is most often peripheral with ipsilateral pleural effusion [4]. On CT and MR, PSS heterogeneously enhances with nodular soft-tissue elements and occasional septa; the enhancement pattern is secondary to haemorrhage and necrosis [5]. It occasionally has thin rim enhancement. PSS is isointense to surrounding musculature on T1-weighted sequences [5] with intermediate to high signal intensity on T2-weighted sequences [5, 2]. Fluid-fluid levels can be seen on T1 and T2-weighted sequences due to haemorrhage [2]. Good history and clinical evaluation are necessary to rule out other malignancies like fibrosarcoma, mesothelioma, and leimoyosarcoma as PSS is difficult to diagnose on imaging [2]. Intravenous contrast helps to characterise more cystic PSS from other malignancies [5].
Treatment includes chemotherapy and radiation therapy, although resection is most curative [2, 1]. Synovial sarcomas are extremely sensitive to ifosfamide-based chemotherapy with a 5-year survival rate up to 60% [2]. Although the prognosis is poor in PSS [4], more targeted chemotherapy to a t(X;18)(p11.2;q11.2) translocation in 80-90% of these tumours and specific fusion proteins may improve prognosis [2, 3].
Our case emphasises the importance of synovial sarcomas as a possible primary pleural malignancy, especially in a young patient. It is important to assess for underlying malignancy in settings of unilateral pleural effusion, especially in immunocompromised patients.
