Is methylene diphosphonate bone scan necessary for initial staging of Ewing sarcoma if 18F-FDG PET/CT is performed?

OBJECTIVE: The purpose of this study was to determine whether methylene diphosphonate (MDP) bone scans are necessary during initial staging in patients with Ewing sarcoma (ES) in whom (18)F-FDG PET/CT is performed.

MATERIALS AND METHODS: A retrospective review was performed of patients who underwent FDG PET/CT and MDP bone scan before treatment of newly diagnosed ES from January 2004 to November 2012. Studies were reviewed to document suspected primary and metastatic malignancy. Pathology and imaging follow-up were used to determine the presence or absence of disease at suspected sites.

RESULTS: Sixty patients were identified in whom FDG PET/CT and MDP bone scans were performed before treatment of newly diagnosed ES. Forty-four primary malignancies had a lytic CT appearance, three were sclerotic, and 13 involved only soft tissue. In 11 of 12 patients with osseous metastases, these were detected on PET/CT, with the one false-negative occurring in a sclerotic primary tumor; in nine of 12 patients with osseous metastases, these were detected on MDP bone scan, with the three false-negatives occurring in patients with lytic primary tumors. Only one of 13 patients with a soft-tissue primary malignancy had bone metastases on both bone scan and PET/CT. PET/CT also showed that eight patients had lung metastases and three patients had lymph node metastases, which were not evident on MDP bone scan.

CONCLUSION: When ES is lytic, MDP bone scan does not add to staging performed by FDG PET/CT; thus, MDP bone scanning may be omitted. However, when ES is sclerotic, MDP bone scan may detect osseous metastases not detected by FDG PET/CT.