[Metastatic alveolar soft tissue sarcoma of the central nervous system: a clinicopathological analysis of four cases].

Background and objective: Metastatic alveolar soft tissue sarcoma (ASTS) of the central nervous system is rare and is easy to be misdiagnosed as other primary tumors of central nervous system. This study was to analyze the clinical and pathological features of four patients with ASTS of the central nervous system and to clarify their differential diagnosis as well as prognosis.

Methods: HE slices and clinical data of the four cases were reviewed and immunohistochemical staining was performed. Antibodies included Vimentin, Myosin, Myoglobin, S-100, Actin, Desmin, CgA, Syn, NSE, and CK.

Results: All four patients had a skin nodule of the extremities removed previously. Clinical symptoms included headache and sight blurring. The metastatic lesions were located in the posterior cranial fossa, closely associated with the meninges. The tumor cells had clear or eosinophilic cytoplasm and prominent nucleoli, arranged in alveolar structures, which were surrounded by delicate blood sinuses. The immunohistochemical staining results showed that the positive stainings of Actin, Desmin and S-100 were in 2 cases; the weakly positive stainings of NSE and Vimentin were in 1 case; the positive staining of PAS was in all four cases. The follow-up data showed that one case died during one year after surgery, two cases died during three years. The fourth case had half year after operation and had been alive without tumour.

Conclusion: ASTS of the central nervous system was mostly metastatic and should be differentiated from other CNS tumors such as meningioma, melonocytic tumor, rhabdomyosarcoma and paraganglioma. Metastatic ASTS of the central nervous system had poor prognosis and the five-year survival rate was low.