Primary Malignant Synovial Tumor in the Mediastinum.

Primary mediastinal synovial sarcomas constitute a rare subset of mediastinal tumors. The diagnosis is often delayed at the time of presentation impacting the five-year survival rate due to its highly aggressive natural history. We report a 22-year old female with a monophasic variant of the primary mediastinal synovial sarcoma. A 22-year-old female, with a two-month history of productive cough, fever, breathlessness, was referred to our center in view of persistent right-sided hydropneumothorax despite multiple thoracocenteses. Examination revealed reduced right-sided air entry with a succussion splash. Imaging suggested a well-defined cystic lesion with fluid, air foci, and multiple septations. A provisional diagnosis of a ruptured hydatid cyst was made and exploratory thoracotomy was planned. Intraoperatively, a well-defined cystic lesion with 350 mL of hemorrhagic fluid, densely adherent to the lung and diaphragm, was found. The biopsy revealed a monophasic spindle cell variant of the primary synovial sarcoma. Follow-up positron emission tomography (PET) on postoperative day 20 showed no residual disease and evidence of metastasis. However, the patient was lost to follow up following one cycle of chemotherapy with ifosfamide. Primary mediastinal synovial sarcomas are aggressive tumors that warrant an early diagnosis for prompt treatment. They usually present with non-specific respiratory symptoms. The gold standard of diagnostic modalities is a molecular panel looking for the translocation - t(X;18)(p11;q11). However, in low-middle income countries, a biopsy may be more practical, as they are cost-effective. The treatment is surgical resection, with combined chemotherapy and radiotherapy if metastases are present. Our case emphasizes the early detection of this lesion, its mimicry with other lesions, and the impact of early diagnosis.