Extraosseous Ewing's Sarcoma Masquerading as Adolescent Neck Mass-a Case Report and Review of Literature.

Ewing sarcoma (ES) is a rare type of malignant bone tumor that arises from mesenchymal stem cells. It commonly occurs in the diaphysis and diaphyseal-metaphyseal portions of long bones, pelvis, and ribs, although any bone can be affected. A minority of the Ewing sarcoma also arise in soft tissues, and a primary tumor in the neck with metastasis is extremely uncommon. We are reporting the case of a 12-year-old female with a history of fever for 4 months and a neck mass for 3 months. Given the broad range of inflammatory and neoplastic etiologies, an extensive laboratory and imaging workup was conducted. Cervical lymph node biopsy for histopathology showed sheets of round blue cells consistent with the diagnosis of Ewing sarcoma in the neck, while a positive immunohistochemical assays for NKX2.2, and negative assay for PAX-5, TdT markers neurofilament, neuron-specific enolase, and S100 protein ruled out the alternative etiologies such as rhabdomyosarcoma and lymphoma. After surgical excision of tumor, chemoradiotherapy was initiated. Despite the typically benign nature of extraosseous Ewing tumors, they can rarely metastasize in less than 20% of cases, as exemplified by this rare case. Accurate diagnosis requires a combined clinic-radio-immunohistochemical approach, and general practitioners should be aware of this clinical entity in neck masses considering its variable clinical presentation and poor prognosis in certain patient's population.