The complex cytological features of synovial sarcoma in fine needle aspirates, an analysis of four illustrative cases

Objective:  The cytological features of conventional monophasic spindle cell and biphasic synovial sarcoma have been defined in detail in several large series. The cytology of rare morphological variants, especially the subtypes of poorly differentiated synovial sarcoma, are insufficiently evaluated and diagnostically difficult to define. The objective of the present study was to call attention to the variable cytology of rare variants of synovial sarcoma. Furthermore, adjunctive diagnostic methods, necessary for a correct diagnosis, are discussed. Methods:  Aspirates from four synovial sarcomas, with cytological features, which differed from those of conventional synovial sarcoma and from each other, were retrieved from our files and re‐evaluated. Results:  In three of the cases a correct diagnosis was not obtained from routinely stained aspirates. In the fourth case, the correct diagnosis was established by a combination of cytomorphology, immunocytochemistry and fluorescence in situ hybridization (FISH) performed on the aspirated material. Conclusion:  Ancillary diagnostic methods are necessary in the examination of aspiration smears from synovial sarcoma, especially of morphological variants with a cytomorphology that differs from conventional spindle‐cell monophasic and biphasic tumours. Immunocytochemistry and molecular genetic examinations (reverse transcriptase polymerase chain reaction or FISH) are the methods of choice.