Xanthogranulomatous osteomyelitis of femur masquerading as neoplasm

Xanthogranulomatous osteomyelitis (XO) is a very rare chronic granulomatous inflammation. It can mimic malignant bone tumors on its clinical presentation, gross features, and radiological imaging. However, histopathological examination can differentiate it from malignancy. We describe the case of a 20-year-old male presented with fever and pain in the right knee joint for 4 months. Plain radiography and magnetic resonance imaging of the right knee joint revealed osteolytic lesion in the lower metaphyseal region of femur. With this clinical presentation and radiological imaging, a diagnosis of primary bone tumor was made. However, XO was confirmed by histopathological examination. This case highlights the rare occurrence and also it can mimic as bone tumor.