Monostotic femoral Caffey disease masquerading as Ewing sarcoma

We describe a rare case of monostotic infantile cortical hyperostosis (Caffey disease) involving the left femur of an infant, who presented with recent onset left thigh swelling, following vaccination. Radiological workup showed a lamellated periosteal reaction involving the left femoral diaphysis on radiographs masquerading as a bone tumour. The child underwent MRI of the left thigh, which showed extensive muscle oedema without any abnormal soft-tissue proliferation, marrow signal alteration, cortical breach or collection. The follow-up radiograph showed exuberant new bone formation in the second week. The patient was given symptomatic treatment and the parents were counselled. The child recovered well with gradual resolution of symptoms and bony remodelling on a 6-month follow-up radiograph. Here, we describe the serial changes on the radiographs in Caffey disease with monostotic involvement and the role of MRI in difficult cases to differentiate it from other common mimickers, such as infections and neoplasia.