Various Morphological Patterns of Synovial Sarcoma, their biological behaviour & prognostic value-a retrospective study of 25 cases

Abstract

Synovial sarcoma occurs at any age but peak age is between 10–35 years with slight male predominance. More than 60% occur in lower limb especially thigh, knee and ankle joints. Synovial sarcoma falls in to two main groups: Biphasic and Monophasic spindle cell type. The latter is more common depending on sampling. The other histological variants are the branching, hemangio pericytoma like pattern. Poorly differentiated with round cell morphology resembling Ewing's sarcoma. Immunohistochemically in addition to epithelial component, spindle cell component also show focal positivity for EMA and keratin. This helps in distinguishing monophasic synovial sarcoma from peripheral nerve Sheath tumor or fibrosarcoma. The aim of this retrospective study is to study the various morphologic patterns of clinically suspected synovial sarcomas, their biological behaviour and prognostic value by immunohistochemical study. A total of 25 cases of clinically suspected cases of synovial sarcoma were studied in the age group of 10–50 yrs. The most commonest age group were in children & young adults between 10–25 yrs. Among 25 cases, 20 cases were in males & 5 in females indicating male dominance. The commonest site involved was knee and ankle joints & in very few cases showed lesions over the shoulder and hip, rare cases over the anterior abdominal wall & in blood vessels. Microscopically Monophasic synovial sarcoma was the common variant seen in 16 biopsies. Presence of short and plump spindle shaped cells arranged in fascicles, compact sheets with tapering nuclei and poorly defined cytoplasm was seen in 15 biopsies, these biopsies also showed cleft like spaces. Whereas four biopsies showed myxoid change. Four cases of monophasic synovial sarcoma showed atypical mitotic figures > 15/10hpf. Four cases of monophasic synovial sarcoma showed focal positivity for epithelial membrane antigen and keratin. One case of poorly differentiated synovial sarcoma was CK7 positive. Poorly differentiated synovial sarcoma showed cytogenetically positivity for SyT-SSx1 fusion gene indicating poorer prognosis. Study of various morphlogical variants is essential to know their prognostic value & biological behaviours. Monophasic synovial sarcomas have more tendency to recur compared to the biphasic variants. Although histopathological study of synovial biopsy is one of the most valuable means for diagnosis of synovial sarcoma, it has its own limitations. In many instances corroborative clinical, radiological, immunohistochemical studies becomes essential in making an accurate histopathological diagnosis.