This 17 y/o female was referred for abdomino-pelvic CT for evaluation of a mass. Selected images are shown above. There is a large heterogeneous abdomino-pelvic mass with septated low attenuation regions and areas of heterogeneous soft tissue attenuation with calcification formation. There is irregularity of the peritoneal surfaces consistent with tumor implantation. Note is made of dilitation of the right renal pelvis consistent with urinary obstruction. Surgical resection of the mass with extensive sampling of the peritoneal implants was performed. The peritoneal implants were shown to be mature glial elements. A final pathologic diagnosis of grade 1 immature teratoma with gliomatosis peritonei was established.