99 mTc-MDP Bone Scan Staging of Vertebral Chordoma.

RATIONALE AND OBJECTIVES: This study aims to evaluate planar 99 mTc-MDP bone scan in vertebral chordoma staging and compare scintigraphy with computed tomography (CT) morphology. MATERIALS AND METHODS: An IRB-approved retrospective review was performed for patients with biopsy-proven chordoma who underwent planar 99 mTc-MDP bone scan and CT within three months of diagnosis. Lesion location, degree of primary uptake, foci of additional uptake, size, and CT morphology were recorded. RESULTS: Fifty-six patients (31 M, 25 F, mean age 56.8 ± 16.3 years) with 43 sacrococcygeal, 8 lumbar, and 5 cervical spine lesions had mean tumor dimensions of 7.1 ± 5.2 cm. On CT, lesions demonstrated characteristics including occult, purely lytic, lytic with surrounding reactive/sclerotic bone, and mixed lytic/sclerotic. On bone scan, lesions demonstrated uptake, ranging from photopenic to marked uptake. There was no association between the pattern of bone involvement and degree (p = 0.45) or presence (p = 0.29) of uptake, or lesion size and degree (p = 0.381) or presence (p = 0.092) of uptake. 17 patients had focal uptake on bone scan suspicious for osseous metastasis, but further workup confirmed true metastasis in only one patient. Alternative etiologies for bone scan uptake were most commonly due to primary benign bone lesions, degenerative changes, and fracture. CONCLUSION: A considerable proportion of vertebral chordomas are occult on planar 99 mTc-MDP bone scan, irrespective of their pattern of bone involvement on CT. Osseous metastases from chordoma are uncommon at initial staging, and bone scan is prone to false positive findings. These results question the routine use of bone scan in staging vertebral chordoma.