[Retroperitoneal extraskeletal Ewing'ｓ sarcoma difficult to differentiate from adrenocortical carcinoma : a case report].

A 15-year-old man complained of left upper abdominal distention. Ultrasonography, computed tomography, and magnetic resonance imaging (MRI) revealed a large multilocular tumor measuring 15×10×14 cm in the left retroperitoneal space. MRI showed the high intensity tumor on the T1 and T2 weighted images and enhanced septum above the left kidney. Positron emission tomography revealed high uptake(SUV max 7.9) in the marginal region. Because the left adrenal gland could not be identified on images, we diagnosed the tumor as adrenocortical carcinoma, preoperatively. In February 2010, tumor excision combined with left nephrectomy and adrenalectomy was performed via transperitoneal approach. Left adrenal gland was identified separately from the tumor, but a small tumor was observed in the gland. The pathological specimen showed sheet-like monotonous proliferation of small round cells which had glycogen. Immunostaining technique showed highly positive CD-99 and neuron specific enolase (NSE). Fluorescence in situ hybridization (FISH) showed translocation of EWS gene. Similar pathological findings were observed in the left adrenal tumor. We diagnosed the tumor as retroperitoneal extraskeletal Ewing' s sarcoma with metastasis to the left adrenal gland. Considering it a high risk, we started adjuvant VAIA(vincristine, dactinomycin, ifosfamide, and doxorubicin) chemotherapy soon after the operation. However, there was left retroperitoneal recurrence 9 months after the operation. We changed the chemotherapy regimen to gemcitabine and docetaxel and are continuing chemotherapy.