Ewing sarcoma of proximal tibial epiphysis: An unusual presentation with review of literature

Ewing's sarcoma/Primitive neuroectodermal tumor (ES/PNET) of bone is a rare childhood tumor most commonly located in the metadiaphysis. It is more commonly seen in the appendicular skeleton and typically involves femur, tibia, humerus or fibula. Within the long bones, the tumor is always metaphyseal or diaphyseal (mid-diaphysis: 33%, metadiaphysis: 44%, metaphyseal: 15%). Rarely 1%-2% of ES may involve epiphysis. In skeletally immature patients, lesions of the epiphysis are rarely malignant, with the most common diagnosis benign chondroblastoma. We report a case of ES of the tibial epiphysis in a 16 year old boy presenting with complaints of pain around right knee joint for six months associated with fever and restricted mobility of knee joint. Magnetic resonance imaging (MRI) of the patient's right knee revealed a large lesion in the centre of upper tibial epiphysis showing hypointense signal on T1 & T2W1 extending from the articular surface through the epiphyseal plate into the upper metaphyseal region. MRI findings suggested an infective pathology with differential diagnosis of Brodie's abscess and chondroblastoma. Based on the imaging characteristics, the patient's age and the lesion's location a preliminary diagnosis of chondroblastoma was made. Debridement and curettage of the lesion was performed and sent for histopathological examination. Microscopy and subsequent immunohistochemistry confirmed it to be a case of ES. An extensive research of literature was done and very few reports Of ES at epiphyseal location were found which make our case worth reporting. This case highlights the rarity of epiphyseally located Ewing sarcoma cases and thus suggesting that the diagnosis of ES should also be considered for pediatric epiphyseal tumors.