Primary renal synovial sarcoma: A case report

BACKGROUND: Synovial sarcoma, a rare mesenchymal tumor type with unclear histological origin and direction of differentiation, accounts for 6%–10% of soft tissue tumors. It is mainly located near the joints and tendons of the limbs, and occurs primarily in children or young adults. Primary renal synovial sarcoma (PRSS) is very rare, accounting for approximately 1% of synovial sarcomas. It is a spindle cell tumor type affecting mesenchymal tissue, and has morphological, genetic, and clinical characteristics, and a certain degree of epithelial differentiation. It is highly malignant and has the fourth highest incidence among soft tissue sarcomas. Here, we report a case of PRSS and share some valuable information about the disease. CASE SUMMARY: A 54-year-old male patient was admitted to the hospital for a space-occupying lesion in the right kidney for 2 d upon ultrasound examination. The patient had no cold or fever; no frequency, urgency or pain of urination; and no other discomfort. The results of a hemogram, blood biochemistry, and tumor markers were in the normal range. The patient was examined by computed tomography (CT), which indicated the presence of a soft tissue density shadow with a diameter of approximately 6.8 cm in the right renal pelvis area, showing uneven enhancement. Ultrasound indicated a cystic solid mass of approximately 6.8 cm × 6.5 cm in the right kidney, with an unclear boundary and irregular shape. Meanwhile, color Doppler flow imaging showed dotted blood flow signals in the periphery and interior. Contrast-enhanced ultrasound (CEUS) showed "slow in and fast out" hyperenhancement of the right renal mass after contrast agent injection. The postoperative pathological diagnosis was (right kidney) synovial sarcoma. Despite postoperative adjuvant chemotherapy, tumor recurrence was detected two years later. CONCLUSION: PRSS is a rare malignant tumor. To date, no characteristic imaging findings have been observed. The diagnosis is confirmed primarily through postoperative pathological immunohistochemistry and SS18 (SYT) gene detection. In this case, CEUS was used preoperatively. We found that PRSS has the characteristic of "slow in and fast out" hyperenhancement, and its particular characteristics have diagnostic value. Postoperative adjuvant chemotherapy is not very effective.