Ganglioneuroblastoma arising within a retroperitoneal mature cystic teratoma

We discuss an extremely rare case of ganglioneuroblastoma arising within a retroperitoneal mature cystic teratoma. Radiological examinations showed a cystic tumor sandwiched between the pancreas and left kidney. Surgery was scheduled because the tumor seemed to have originated from the pancreas. En-block resection of the tumor with distal pancreatectomy, splenectomy, and left adrenalectomy was performed. In terms of macroscopic appearance, the tumor mainly consisted of a unilocular cystic mass, but the presence of a smaller, solid mass was also noted within the tumor. Histopathologic examination confirmed that the cystic mass was consistent with a mature cystic teratoma of the retroperitoneum, and in addition, a ganglioneuroblastoma was evident in the solid component. Histopathologically, the ganglioneuroblastomatous area was intimately associated with dermoid tissue of the mature cystic teratoma, thus this case was diagnosed to be a mature cystic teratoma with malignant transformation. To best of our knowledge, this is the first reported case of ganglioneuroblastoma arising in a mature cystic teratoma.