METALLIC FOREIGN-BODIES IN THE ORBITS OF PATIENTS UNDERGOING MR-IMAGING - PREVALENCE AND VALUE OF RADIOGRAPHY AND CT BEFORE MR

OBJECTIVE. The purpose of this study was to measure the prevalence of metallic foreign bodies in the orbits of 15,024 patients who were sche duled for MR imaging during a 4-year period and to determine if screen ing by plain radiography, CT, or both before MR imaging is efficacious . MATERIALS AND METHODS. Records of 15,024 patients scheduled for MR i maging were reviewed. A total of 1593 patients who had identified them selves as being at risk for an intraorbital metallic foreign body had undergone plain radiography or CT of the orbits. Plain radiographs and /or CT scans of patients reported as having orbital metal were reviewe d to confirm the presence of a metallic foreign body and to identify i ts location. RESULTS. Metallic foreign bodies were discovered in 40 pa tients. Six of these patients had impaired vision in the involved eye. Ten patients had a metallic foreign body in or near the orbit but wel l away from the globe and were thought to be at low risk for movement of the foreign body as a result of MR imaging. The other 24 patients h ad metallic foreign bodies adjacent to or within the globe and were th ought to be at risk for movement of the metallic foreign body as a res ult of MR imaging. CONCLUSION. The prevalence of intraorbital metallic foreign bodies in our study population was low (0.27%). Even in those patients identified as being at risk, the prevalence was only 2.5%. B ased on the number of MR examinations performed annually in the United States and on data indicating that no radiographic screening is perfo rmed at 5% of institutions, we extrapolate that more than 2400 patient s with intraorbital metallic foreign bodies have undergone MR imaging since 1986 without report of injury. These data allow us to infer that the risk of eye damage for patients who have intraorbital metal is lo w and that radiographic screening before MR imaging is not needed as o ften as it is done.