The Imaging Spectrum of Synovial Sarcomas: A Pictorial Review From a Single-Centre Tertiary Referral Institution.

Synovial sarcomas are malignant soft-tissue tumors that typically affect young patients. They can arise from nearly anywhere in the body, most commonly the extremities, head and neck, and thorax. The imaging features are highly variable and depend on the anatomic origin. Most lesions present as large aggressive heterogeneous masses containing hemorrhagic and cystic foci, often with calcification. However, up to one-third of lesions have commonly benign features and can appear homogeneously solid or cystic. Especially in these cases, their innocuous imaging and clinical presentation can lead to delayed diagnosis. Therefore, knowledge of the imaging spectrum is crucial to ensuring adequate follow-up or timely pathologic sampling. We reviewed 30 pathologically proven cases in various anatomic sites from our institution to illustrate these characteristics.

Sox9, a master regulator of chondrogenesis, distinguishes mesenchymal chondrosarcoma from other small blue round cell tumors.

Over the last decade, a number of "master regulator" genes that control distinct pathways of mesenchymal differentiation have been discovered. These genes are expressed early during embryogenesis and initiate a cascade of gene expression responsible for specific cell lineage commitment. Thus, identification of their products may allow the classification of seemingly primitive, morphologically uncommitted tumors such as small blue round cell tumors. The transcription factor Sox9 has been demonstrated to be a master regulator of the differentiation of mesenchymal cells into chondrocytes. For this reason, we examined the utility of Sox9 in distinguishing mesenchymal chondrosarcoma (a small cell malignancy thought to be derived from primitive chondroprogenitor cells) from other primitive small cell malignancies. Representative sections from 90 cases of small blue round cell tumors (22 mesenchymal chodrosarcoma, 10 neuroblastomas, 11 rhabdomyosarcomas, 9 Ewing's sarcomas/primitive neuroectodermal tumors, 5 desmoplastic small round cell tumors, 7 small cell carcinomas, 6 Merkel cell carcinomas, 6 small cell osteosarcomas, 7 diffuse large B-cell lymphomas, 7 lymphoblastic leukemias/lymphomas, and 5 extraskeletal myxoid chondrosarcomas) were immunohistochemically stained with antibodies to Sox9 protein. All but 1 mesenchymal chondrosarcoma showed positive nuclear staining in both primitive mesenchymal and cartilaginous components of the tumor. All other types of small blue round cell tumors, as well as the lymphomas and leukemias, were negative for Sox9 protein. These findings confirm that mesenchymal chondrosarcoma has phenotypic features corresponding to the early condensational phase of cartilaginous differentiation. More important, Sox9 may serve as a useful tool in the differentiation of small cell malignancies.