Tumefaction of the Parotid Region in a 10-Month-Old Infant Revealing a Synovial Sarcoma: A Diagnostic Challenge, Case Report, and Review of the Literature.

Synovial sarcoma (SS) is a malignant mesenchymal proliferation most commonly found near the large joints and bursae of the lower extremities. It is rarely found in the head and neck region. The objective of our study is to report a female infant with SS of the right parotid gland. She did not present any particular pathological history and presented with a right laterocervical tumefaction rapidly increasing in size. Clinical examination showed a non-pulsatile, non-tender, and firm mass in the right parotid region measuring 7 cm x 5 cm with no local signs of aggression. Facial CT and MRI scans showed a lesion centred on the right parotid region, which was locally aggressive and displaced adjacent structures without invading them. Microscopic examination of the surgical biopsy revealed a spindle cell tumor proliferation, heterogeneous in cell density, not very atypical, with the presence of a few tubes and clusters of epithelial cells that resembled the ducts and acini of the normal parotid gland. After an immunohistochemical study, the diagnosis made was that of a SS with a double fusocellular and epithelial component. Molecular confirmation was obtained by searching for the SS18 gene translocation characteristic of synovial sarcoma using the Fluorescence in Situ Hybridization (FISH) technique, the result of which was positive. SS is an aggressive type of sarcoma and is considered the leading cause of non-rhabdomyosarcoma soft tissue sarcomas in children and adolescents. Diagnosis is obtained by histological and immunohistochemical analysis of the tumor, complemented by a search for the specific t(X;18) translocation, found in over 90% of cases. The treatment of SS differs according to age. The use of perioperative chemotherapy followed by surgery and then radiotherapy is more common in pediatrics and may improve the prognosis and reduce the risk of recurrence and metastasis.