Original Research Article DOI: 10.18231/2394-6792.2018.0058 Indian Journal of Pathology and Oncology, April-June, 2018;5(2):308-313 308 Ewing sarcoma of proximal tibial epiphysis: An unusual presentation with review of literature Ruchi Sinha 1 , Iffat Jamal 2,* , Amar Kumar 3 , Anup Kumar 4 1,4 Addtional Professor, 2 Senior Resident, 3 Tutor, 1-3 Dept. of Pathology/Lab Medicine, 4 Dept. of Orthopaedics, All India Institute of Medical Sciences, (AIIMS) Patna, Bihar, India *Corresponding Author: Email: iffatjamal111@gmail.com Received: 17 th July, 2017 Accepted: 11 th November, 2017 Abstract 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. Keywords: Ewing tumor, Primitive neuroectodermal tumor, Metadiaphysis, Epiphysis, Metaphyseal, Chondroblastoma. Introduction Ewing sarcoma is the second most common primary malignant bone tumour of childhood and adolescence following osteosarcoma. 1 Diaphysis of the long bones (femur, tibia and humerus), flat bones like ribs, scapula and pelvis are the preferred sites of ES. 2 Involvement of proximal metaphysis of tibia is rare with a reported incidence of 4-11 %. 3 Rarely 1%-2% of ES may involve epiphysis. 4 Clinically ES may present as a localized, painful mass or with systemic symptoms such as fever, malaise, weight loss, leucocytosis and increased erythrocyte sedimentation rate. 5 Radiologically, the most common finding in ES is a lytic lesion but there may be regions of increased density due to stimulation of new bone formation. As the tumor invades through the cortex, it often elevates the periosteum gradually. This elevation produces the characteristic multiple layers of subperiosteal reactive new bone, which produces the onionskin appearance. 6 The differential diagnosis of epiphyseal bone lesions in children include infections, enchondroma, chondroblastoma, giant cell tumor, clear cell chondrosarcoma and langerhans cell histiocytosis. 7 Malignant lesions of epiphysis are rare. A large series of 2758 tumor cases from a German tumor registry in 1996 found no cases of primary malignant bone tumor of the epiphysis and fewer than 10 cases of primary osteosarcoma of the epiphysis. No case of ES was found. 7,8 This article presents a case of primary ES/PNET of the proximal tibial epiphysis in a 16 year old boy. Epiphyseal location of Ewing’s tumour is a very rare occurrence and only 1% to 2% of cases have been reported so far in English literature which makes our case worth reporting. Case Report A 16 year old boy presented with pain around knee joint for 6 months with restricted mobility of the joint and associated persisting low grade fever. Magnetic resonance imaging (MRI) showed a large, 4.6x1.9 cm lesion in the centre of tibial epiphysis showing hypointense signal on T1 & T2W1, extending from the articular surface through the epiphyseal plate into the upper metaphyseal region. (Fig. 1) MRI findings was reported as an infective pathology like Brodie’s abscess with a differential diagnosis of chondroblastoma. Based on the imaging characteristics, the patient’s age, and the lesion’s location, a presumptive clinical diagnosis of chondroblastoma was made. Debridement and curettage was done and the tissue was sent for histopathology. Grossly, multiple dark brown soft tissue bits admixed with bony fragments altogether measuring 3.5x2.5x1.5 cm were received. Microscopy revealed presence of