Mucinous, gland predominant synovial sarcoma of a large peripheral nerve: a rare case closely mimicking metastatic mucinous carcinoma.

Synovial sarcoma is a distinctive soft tissue neoplasm with monophasic and biphasic forms. It is typically a deep-seated soft tissue tumour of the extremities of young adults and occasional cases have been described in large peripheral nerves. A rare example has a predominance of the glandular component and may mimic metastatic carcinoma. Here, a unique synovial sarcoma with <1% spindle cell component involving the posterior tibial nerve is decribed. In addition to having only small bands or islands of stroma, there was also mucin dissection of the surrounding soft tissue. Isolated glands were seen "floating" in pools of mucin. There was abundant intracellular mucin present as well. These latter two findings have not been described in synovial sarcoma thus far, to our knowledge. The diagnosis was confirmed by molecular detection of the t(X;18) by reverse transcription-PCR and confirmed by dual colour break apart fluorescence in situ hybridisation, in a second laboratory. Mucinous, gland predominant synovial sarcoma must be recognised to avoid misdiagnosis of metastatic carcinoma or a glandular malignant peripheral nerve sheath tumour when occurring in a peripheral nerve.