Pediatric case of the day. Ewing sarcoma of pubic bone.

This i 5-year-old girl complained of intermittent left-sided groin pain for 2 years. She had no history of trauma, infection, or constitutional symptoms. Physical examination revealed fullness in the left inguinal region, but no discrete mass could be palpated. The plain radiograph of the pelvis (Fig. 1 A) revealed bony destruction of the left superior ramus and symphysis with a lamellated periosteal reaction. The bladder was displaced to the right by a large soft-tissue mass. A bone scan (Fig. 1 B) showed markedly increased uptake in the left superior and inferior rami, symphysis, and acetabulum. The extent of the tumor mass was then evaluated by MR imaging. Ti -weighted coronal (450/20) and axial (700/20) images (Figs. 1 C, 1 D, and 1 F) and T2-weighted axial (3000/80) images (Figs. 1 E and i G) showed a large soft-tissue mass encasing the left superior ramus with extension into the pelvis. The mass was isointense to muscle on Ti -weighted images and heterogeneously increased on T2-weighted images. Bladder wall invasion and bone marrow signal change in the left acetabulum were noted. An open biopsy was performed, and the histologic diagnosis was Ewing sarcoma. Ewing sarcoma is a malignant bone tumor usually seen in patients between the ages of 5 and 1 4, rarely seen in patients over the age of 30 [1 ]. Overall, it is the second most common primary malignant tumor of bone in children and accounts for 1 0% of all primary bone tumors. In the pelvic bones, it is the most common primary malignant tumor [2]. The cell of origin is unknown, but it is thought by some to arise from a stemcell precursor [3]. Clinically, there is a well-known delay in diagnosis. Patients will often have constitutional symptoms of malaise and fever with a leukocytosis suggesting an infection. When the pelvic bones are involved, poorly localized pain and a progressive limp are common [2]. Twenty percent of patients have metastases at the time of diagnosis, generally involving the lungs and other bones [4]. Plain radiography is the best imaging method for assessing the tumor and predicting the histologic diagnosis [1 , 5]. There are four types of radiographic changes: diffuse sclerosis, diffuse osteolysis, mixed sclerosis and osteolysis, and permeative osteolysis [2]. The peniosteal reaction may be larnellated or sunburst, and there may be a Codman’s triangle. The tumor can occur at any skeletal site, occurring more often in the diarnetaphyseal region of long tubular bones in patients younger than 1 8 years old and in the flat bones in older patients [i]. MR imaging is most useful in evaluating the extent of bone and soft-tissue involvement for preoperative and pretreatment planning [5]. The tumor is characteristically of decreased signal on Ti -weighted images and increased signal on T2weighted images [6]. After surgery or radiotherapy, a decreased signal on T2-weighted images has a high sensitivity for tumor sterilization. Continued increased signal on T2weighted images may indicate residual tumor, inflammatory changes from radiation, or postoperative hematoma. Gadopentetate dirneglumine induces a signal enhancement of both active tumor and inflammatory changes, adding little to longterm follow-up [5]. The differential diagnosis of this tumor should include osteomyelitis, osteosarcorna, eosinophihic granulorna, nonHodgkin lymphorna, and rnetastatic disease [2]. Survival rates have improved with aggressive adjunctive chemotherapy and megavoltage irradiation. The estimated 5year survival rate is currently 1 5%. The most important predictor of prognosis is the primary site. Primary tumors of the pelvic bone have the lowest survival rate [1].