MB-07: PRIMARY EWING SARCOMA OF THE SCALP WITH APPARENT EPIDURAL EXTENSION: CASE ILLUSTRATION

INTRODUCTION: Ewing sarcoma is an aggressive, rapidly growing, malignant tumor originating from postganglionic parasympathetic neural crest cells, most commonly originating in the pelvis and long bones. We describe a rare case of primary Ewing sarcoma of the scalp, in which imaging was suggestive of intracranial extension not seen on operative exploration. CASE REPORT: An 11 year old boy with a rapidly growing subcutaneous mass on the forehead was diagnosed with Ewing sarcoma by needle biopsy. Brain CT and MRI showed an extracranial mass with a smaller corresponding epidural lesion. Metastatic evaluation was negative. The patient was treated with chemotherapy to shrink the lesion, followed by surgical resection of the residual mass. In surgery, only partial-thickness erosion of the extracranial tumor mass through the bone was observed. The involved area of skull with margins was removed as a single bone flap. The inner table of the bone and epidural space appeared grossly normal, and there was no subdural mass on ultrasound. The patient subsequently completed further chemotherapy and radiation, and has remained disease-free. No residual or recurrent abnormal tissue has been seen on surveillance imaging. DISCUSSION: Ewing sarcoma of the scalp is a rarely reported disease entity, relatively less common than primary disease of the skull. Good outcomes have been reported when wide local excision is carried out. The phenomenon of radiographic epidural pseudoextension has not previously been described and does not seem to have adversely affected outcome in this case. CONCLUSIONS: MRI may overestimate extent of disease in cases adjacent to the epidural space. In cases of localized disease, wide local excision combined with chemotherapy and radiation can offer significant progression-free survival.