Nuclear imaging of an extraskeletal retroperitoneal osteosarcoma: respective contribution of 18FDG-PET and (99m)Tc oxidronate (2005:1b).

Extraskeletal osteosarcoma (ExOs) is a rare, usually highly aggressive malignancy, which affects individuals beyond the fifth decade of life. ExOs prinicipally occurs as a soft tissue mass in a limb or retroperitoneum. We present the case of a 58-year-old man with a huge abdominal mass who underwent a complete range of clinical imaging investigations including computed tomography (CT), skeletal scintigraphy (BS) and positron emission tomography (PET). These exams showed a central calcified and ossified, strongly metabolic retroperitoneal tumour suggestive of an ExOs. This diagnosis was later confirmed by histopathology. To our knowledge, such a case has not previously been documented fully using radiological imaging correlated to modern nuclear medicine techniques such as PET.