Ewing’s sarcoma accounts for 4–6% of primary malignant bone tumors and it affects the head and neck in only 1–4% cases. It is a rare undifferentiated, round and small-cells tumor of uncertain histogenesis. A 16-year-old female patient presented extrusion, accentuated mobility and slightly sintomatology at 36 tooth. Radiographically radiolucent round areas involving the apical region of 36 tooth were observed. The CBCT exam showed hypodense area with destruction of lingual plate nearby to the 36 tooth. Exploratory surgery was performed with lingual access discovering an empty cavity. Twenty days afterwards, the patient returned without mobility at the teeth, suggesting the diagnostic of Simple Bone Cyst. After thirty days, the patient presented vestibular growth, pain, considerable dental mobility (36 and 37 teeth), regional lymphadenopathy suggesting cyst’s secondary infection. CBCT exam showed enlargement of hypodense area of approximately 1 cm of the initial appearance, the lesion was submitted to a surgical curettage and the involved teeth were removed. Microscopically, it was showed tumor fibers and isolated islands formed predominantly by small round cell, with wide hyperchromatic and well-defined nucleus, eosinophilic or vacuolated cytoplasm with ill-defined margins, consistent with the diagnosis of primitive neuroectodermal tumor/Ewing sarcoma. Immunohistochemical panel showed PAS without positive diastase, strong and diffuse coloration (approximately 100% of tumor cells) for vimentina and positivity for S-100, NSE and CD99. CT and PET scan of the patient did not detect other foci of tumoral invasion beyond jaw. The patient held antineopasic therapy.

Conflict of interest: None declared.