Eosinophilic granuloma of femoral shaft masquerading as ewing sarcoma: a case report and review of the literature

Introduction: Eosinophilic granuloma (EG) of bone is a rare tumor comprising less than 1% of all bone tumors. The nonspecific clinical and radiological pictures often make the diagnosis difficult. We report a case of EG of Femoral diaphysis that masquerades as Ewing sarcoma.
Case presentation: A 7-year-old child presented with right thigh pain and swelling for 2 months. Radiograph of thigh showed a lytic mid-diaphyseal lesion with endosteal cortical erosion and diffuse circumscribed laminated periosetal reaction with neobone formation (onion skin appearance). Magnetic resonance images revealed hypointense T1W and hyperintense T2W medullary lesion with circumscribed periosteal reaction and neobone formation. Considering the clinical and radiologic features, the provisional diagnosis of Ewing sarcoma was made. But biopsy of the lesion proved it to be an Eosinophilic granuloma of bone. The child was also investigated for other sites to evaluate associated lesions. There was no evidence of any other organ involvement. The solitary bony Eosinophilic granuloma was managed conservatively with regular evaluation of the lesion. At 15-months follow up, the lesion has completely healed and the child is asymptomatic.
Conclusion: Isolated EG of bone in children often arises a radiological confusion with subacute osteomyelitis and Ewing sarcoma. Conclusive diagnosis is established after histological examination of the lesion. The lesion may show spontaneous resolution, and hence a regular clinical and radiological follow up is needed to look for the behaviour of the lesion.