Synovial sarcoma (SS) is a malignant soft tissue tumor characterized by partial epithelial differentiation. It is most commonly seen in young individuals and can arise in almost any anatomical region (1, 2). SS accounts for approximately 10% of all soft tissue sarcomas (STS) (3, 4). In the pediatric population, SS is the most prevalent non-rhabdomyosarcoma STS (5, 6). It is often located near large joints such as the knee and ankle (7), but it can also occur in internal organs (e.g., heart, lungs, pleura, kidney), the oral cavity, mediastinum, retroperitoneum, peritoneum, central nervous system, and peripheral nerves (8). Compared to SS in other anatomical regions, head and neck synovial sarcoma (HNSS) is thought to have a higher likelihood of metastasis, typically spreading hematogenously (9, 10). Only 3%–5% of SS cases occur in the head and neck region (HNR), with SS originating from the tonsils being particularly rare; only two well-documented cases have been reported in the HNR in the English literature (11, 12). The first pediatric case of tonsillar synovial sarcoma was described by Yalçin et al. in 2020 (13). Given its rare localization, the management of tonsillar SS is primarily based on case reports (12, 13). We report what is, to the best of our knowledge, the second pediatric tonsillar SS case in the literature (14). This case, with its unusual location and treatment approach, may add valuable insight to the existing literature.

A 5-year-old girl presented with a 1.5-month history of fever and difficulty swallowing. The physical examination revealed a mass in the right tonsil that narrowed the oropharynx. The right tonsil appeared enlarged with a smooth surface and showed no signs of ulceration. Her medical history was otherwise unremarkable. Contrast-enhanced magnetic resonance imaging (MRI) revealed a solitary mass measuring 30 × 30 × 30 mm in the right lateral oropharynx, extending to the hypopharynx, and irregularly narrowing the oropharyngeal lumen. Given the absence of obvious liquid components within the mass, peritonsillitis or an early peritonsillar (non-organised) abscess was initially suspected (Figure 1). An 18F-Fluorodeoxyglucose-Positron Emission Tomography/Computed Tomography (18F-FDG-PET-CT) scan showed metabolic activity (SUV max: 5.5) in the region of the right tonsil. No distant metastases were observed on the PET scan. PET-CT was performed to exclude the possibility of systemic disease and to guide further diagnostic and therapeutic planning, as the mass was initially suspected to represent an infectious or neoplastic lesion. An incisional biopsy of the right tonsil was performed, and histopathological examination confirmed the diagnosis of biphasic synovial sarcoma.

Synovial sarcoma is a rare soft tissue malignancy, accounting for approximately 8%–10% of all soft tissue neoplasms (15). It typically occurs near large joints, but its presence in the head and neck—an area with limited synovial tissue—is rare (16). Given its rarity, especially in the tonsils, management of tonsillar SS primarily relies on case reports (12, 13). The first pediatric case of tonsillar SS was reported by Yalçin et al. in 2020, who described the successful surgical resection and adjuvant chemotherapy of a similar case (13). We present the second documented case of pediatric tonsillar SS, to the best of our knowledge.

Treatment for SS generally involves surgical excision with negative margins, complemented by chemotherapy and radiotherapy based on the patient's and tumor's characteristics (17). Prognosis for localized SS is generally favorable, with most patients being long-term survivors. However, those with metastatic disease have a poorer prognosis. Tumors larger than 5 cm, invasion, and a high histological grade are associated with worse outcomes (18, 19). In our case, the localized SS was smaller than 5 cm, leading us to believe the prognosis is favorable, though we continued close monitoring for potential metastasis. The role of chemotherapy in pediatric synovial sarcoma remains unclear, with some cases showing good responses only to chemotherapy without the need for surgery (20).

In typical synovial sarcoma cases, complete surgical resection with negative margins remains the cornerstone of therapy. However, in head and neck localizations, achieving clear surgical margins is often limited by anatomical constraints, which necessitates the use of multimodal approaches, including chemotherapy and radiotherapy (21).

This case contributes to the limited literature on the successful management of pediatric tonsillar synovial sarcoma with chemotherapy alone. In our patient, tonsillectomy was not performed at diagnosis due to the risk of perioperative complications, given the tumor size and infiltration of adjacent structures. Instead, a limited incisional biopsy was chosen to obtain tissue for diagnosis. Following chemotherapy, tonsillectomy was not performed as the tumor showed marked regression and complete excision would have entailed significant morbidity.

Compared with the previously reported pediatric tonsillar SS case, where surgery combined with adjuvant chemotherapy achieved remission, our case demonstrates that chemotherapy alone may also provide favorable outcomes when surgery is not feasible. This highlights the importance of tailoring treatment to tumor localization and individual patient risks.

Furthermore, although the tumor was <5 cm and localized, it was classified as FNCLCC grade 3. High-grade histology is usually associated with poorer outcomes, underscoring the need for close surveillance despite the patient's favorable clinical course.

Long-term follow-up is also essential in pediatric patients, not only for recurrence surveillance but also for monitoring potential late effects of chemotherapy, such as cardiotoxicity and impacts on growth or fertility. Multidisciplinary follow-up involving pediatric oncology, cardiology, and endocrinology teams is therefore recommended.

In conclusion, tonsillar synovial sarcoma is an extremely rare malignancy in the pediatric population. Further studies and accumulated case reports are necessary to establish evidence-based treatment strategies and prognostic factors for this tumor. We believe that the management of such rare tumors requires a multidisciplinary approach. Our case highlights the potential role of chemotherapy alone when surgery is not feasible and adds valuable insight into the limited literature on pediatric tonsillar synovial sarcoma.