A 13 year old boy referred to the Oral and Maxillofacial Surgery Department from the Paediatrics Department for 4 days of asymptomatic swelling of the right cheek. He reported no other symptoms and no weight loss.
Physical examination revealed a solid, elliptical mass between the body of the malar bone and the anterosuperior part of the right maxillary bone. There was a boundary between the lesion and the surrounding muscle and it did not infiltrate the skin. Intraoral examination revealed a firm, mobile and painless mass in the gingiva at the bottom of the vestibule of the right upper hemiarch. No other findings were found on examination of the head and neck.
A biopsy was performed with intraoral access. Histologically, the mass consisted mostly of a compact proliferation of small cells. At higher magnification these cells consisted of round, uniform nuclei, revealing granular chromatin with peripheral condensation, as well as scanty, slightly eosinophilic cytoplasm. The stroma was sparse with occasional fibrous tissue tracts. Immunohistochemical analysis showed positivity for CD-99.

Subsequent magnetic resonance imaging (MRI) showed the presence of a well-demarcated, encapsulated solid tumour measuring approximately 24 × 13 mm located anterior to the right maxillary sinus, with anterior displacement of the zygomatic musculature. The lesion did not show infiltration of neighbouring structures and showed intense gadolinium enhancement after gadolinium administration, suggesting high cellularity of the lesion. No underlying bone changes or significant adenopathic growths were identified.

Prior to treatment, distant metastases were ruled out by biopsy and bone marrow aspiration, in addition to a full-body PET-CT scan.
Treatment for ESS was administered following the Euro-EWING 99 protocol. The control MRI showed disappearance of the lesion, although with persistent thickening involving the affected facial musculature (inferior aspect of the orbicularis oculi and levator labii superioris), together with minimal enhancement after contrast administration.
Surgical treatment of the remaining lesion was then performed, with extensive resection of the affected facial musculature and soft tissue. The maxillary bone plane was approached, without resection, as no tumour infiltration was observed either clinically or radiographically.
The patient was discharged on the second postoperative day in good general condition with no postoperative complications.
Histological analysis of the surgical specimen revealed absence of malignant cells and negative margins.
The control MRI findings were described as postoperative changes from the baseline study, with no criteria for underlying tumour recurrence or recurrence.