Recurrent Primary Intracranial Ewing Sarcoma With Parietal Bone Involvement: A Case Report.

Introduction: Ewing sarcoma is a rare, aggressive malignancy of small round blue cells that typically arises from bone or soft tissue. Primary intracranial involvement is exceedingly uncommon, particularly in adults, and is associated with diagnostic challenges, high recurrence rates, and poor prognosis. Limited data exist regarding optimal management strategies for recurrent intracranial Ewing sarcoma in adult patients. Case Summary: We report the case of a 24-year-old pregnant female who presented with progressive headaches, vomiting, and left parietal swelling. MRI revealed a ring-enhancing lesion in the left parietal region with surrounding edema. She underwent surgical resection, and histopathology demonstrated sheets of small round blue cells with strong CD99 positivity. Fluorescence in situ hybridization using an EWSR1 break-apart probe confirmed EWSR1 gene rearrangement; however, fusion partner identification was not available. Based on the morphologic and immunohistochemical features in conjunction with EWSR1 rearrangement, a diagnosis of EWSR1-rearranged round cell sarcoma consistent with Ewing sarcoma was made. Adjuvant therapy was delayed due to pregnancy. Despite subsequent multimodal treatment including surgery, VAC-IE chemotherapy, and radiotherapy, the patient developed local recurrence involving the parietal bone within one year and died four months after recurrence. Conclusion: This case highlights the aggressive nature and high recurrence risk of primary intracranial Ewing sarcoma in adults. Diagnostic confirmation requires histopathological and molecular analysis, as radiological findings may mimic other central nervous system tumors. Early diagnosis, timely multimodal therapy, and close surveillance are critical; however, outcomes remain poor, underscoring the need for improved and individualized treatment strategies for adult intracranial Ewing sarcoma.