Intraosseous synovial sarcoma of the distal ulna: a case report and review of the literature

Abstract

Background: Synovial sarcoma is a relatively rare type of soft tissue sarcoma. The commonly observed symptom is a deep-seated palpable mass accompanied by pain or tenderness. Thus, it is considered a soft tissue sarcoma and rarely occurs primarily in bone. However, only few studies have been reported on intraosseous synovial sarcoma, and reports on cases with cytogenetic or molecular confirmation are even rarer. We report a case of intraosseous synovial sarcoma of the distal ulna that has been confirmed using histopathological examination and molecular analysis.

Case presentation: A 77-year-old female was referred to our hospital with a 1-month history of right wrist pain after housework. Clinical and imaging findings suggested a benign bone tumor that was enhanced by Gd-DTPA. It was thought that the tumor was possibly an enchondroma. Initially, we planned to evaluate the benignancy of the tumor with intraoperative frozen section, followed by curettage and bone graft at one stage However, when considering carefully, characteristics of the tumor did not perfectly match those of any diagnostic categories including enchondroma. Therefore, an incisional biopsy was performed and revealed that the tumor was synovial sarcoma. Following an elaborate plan, the patient underwent a wide resection of the tumor at the distal part of the right ulna. Reverse transcription-polymerase chain reaction (RT-PCR) from the resected specimen and sequencing of RT-PCR products demonstrated a chimeric SYT-SSX1 transcript, confirming the diagnosis of synovial sarcoma.

Conclusions: Synovial sarcoma is seldom considered in differential diagnosis of bone tumors because it is difficult to line up such an unusual diagnosis as a differential diagnosis. When the lesion does not perfectly fit into any diagnostic category, when the initial image diagnosis appears unconvincing, biopsy and pathology are indicated, recalling Jaffe's triangle. According to these diagnostic processes, the patient successfully completed the treatment for this rare intraosseous synovial sarcoma, following a careful plan based on the preoperative diagnosis.

Keywords: Bone tumor; SYT-SSX fusion gene; Synovial sarcoma.

Fig. 1

An anteroposterior plain radiograph of the right wrist. There is a comparatively well outlined osteolytic lesion at the distal end of the ulna

Fig. 2

MRI of the lesion of the distal ulna. a The mass showed iso-intensity on T1-WI, b almost homogenous high intensity on T2-WI, a low intensity line in the proximal end of the lesion suggesting sclerotic rim, and c. was enhanced heterogeneously by Gd.-DTPA. The lesion stayed inside the distal ulna bone; there were no extraosseous masses

Fig. 3

PET-CT imaging. a Whole body scan did not show any distant metastasis nor abnormal FDG uptake in the distal ulna. b Scan of forearm showed no abnormal FDG uptake in the lesion

Fig. 4

Histopathological appearance of the tumor. The specimen was composed of fascicles of spindle cells in a palisading pattern. Most of the lesion showed less aggressive pattern (the left side of a.); however, there was an area that showed partial high cellularity and nuclear atypia (the right side of a, b). Histologic features and immunohistochemistry results suggested a synovial sarcoma. Original magnification; a. × 100, b. × 400

Fig. 5

Postoperative analysis of resected tumor. a Histopathologically, the tumor consisted of spindle cells in a palisading pattern, and occupied the distal end of the ulna. Original magnification; × 200, b Molecular analysis definitely demonstrated the diagnosis of synovial sarcoma by confirming the SYT-SSX fusion gene. The DNA sequence data was identical to the alignment of SYT-SSX fusion gene, including the SSX1 breakpoint