Extraosseous Ewing Sarcoma in the Parapharyngeal Space: A Rare Presentation Posing a Diagnostic Dilemma

Ewing sarcoma (ES) is a highly malignant small round cell tumour predominantly affecting children and young adults. Head and neck involvement is rare, and occurrence within the parapharyngeal space is exceedingly rare. Extraosseous Ewing sarcoma (EES) poses a significant diagnostic challenge due to overlapping clinical and imaging features with other malignancies, particularly nasopharyngeal carcinoma and lymphoma. We report a 23-year-old female who presented with a 6-month history of nasal stuffiness, watery ear discharge, and epistaxis. Magnetic resonance imaging (MRI) revealed a well-defined heterogeneously enhancing mass in the left parapharyngeal space. Histopathology confirmed EES, with immunohistochemistry demonstrating strong membranous CD99 and vimentin positivity. ¹⁸ F-FDG PET/CT revealed an intensely FDG-avid mass confined to the left parapharyngeal region without locoregional nodal or distant metastases, enabling accurate staging and treatment planning. This case underscores the complementary roles of MRI and ¹⁸ F-FDG PET/CT in the workup, staging, and management of this rare entity.