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                                            Safety Information Article
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       Metallic Orbital Foreign Bodies and Screening 

The case report in 1986 by Kelly, et al. regarding a patient that sustained an orbital injury from a metallic foreign body led to substantial controversy regarding the procedure required to screen patients prior to MR procedures. Notably, this incident is one of the few serious eye injuries that has occurred in the MR environment. Accordingly, the policy of performing radiographic screening for orbital foreign bodies in patients or individuals simply because of a history of occupational exposure to metallic fragments must be reconsidered.

A study by Seidenwurm, et al. (2000) evaluated the practical aspects and cost-effectiveness of using a clinical versus radiographic technique to initially screen patients for orbital foreign bodies before MR procedures. The cost of screening was determined on the basis of published reports, disability rating guides, and a practice survey. A sensitivity analysis was performed for each variable. For this analysis, the benefits of screening were avoidance of immediate, permanent, nonameliorable, or unilateral blindness.

The findings of Seidenwurm, et al. support the fact that the use of clinical screening before radiography increases the cost-effectiveness of foreign body screening by an order of magnitude (i.e. assuming base case ocular foreign body removal rates). From a clinical screening standpoint for a metallic foreign body located in the orbit, asking the patient “Did a doctor get it all out?” serves this purpose.

Seidenwurm, et al. (2000) implemented the following policy with regard to screening patients with suspected metallic foreign bodies, “If a patient reports injury from an ocular foreign body that was subsequently removed by a doctor or that resulted in negative findings on any examination, we perform MR imaging. Those persons with a history of injury and no subsequent negative eye examination are screened radiographically.” Of note is that Seidenwurm, et al. (2000) performed more than 100,000 MRI procedures under this protocol without incident.

Thus, an occupational history of exposure to metallic fragments, by itself, is insufficient to mandate radiographic orbital screening. Therefore, guidelines for foreign body screening should be based on this information and because radiographic screening before MR procedures on the basis of occupational exposure alone is neither clinically necessary nor cost-effective.

Clinical Screening Protocol. The procedure to follow with regard to patients with suspected metallic orbital foreign bodies involves asking them if they had an ocular injury. If they sustained an ocular injury, they are asked whether they had a medical examination at the time of the injury and whether they were told by the examining doctor, “It’s all out.” If they did not have an injury, if they were told their ophthalmologic examination was normal, and/or if the foreign body was removed entirely at the time of the injury, then they can proceed to MR imaging.

Radiographic Screening Protocol. Based on the results of the clinical screening protocol, patients are screened radiographically if they sustained an ocular injury related to a metallic foreign object and they were told that the eye examination revealed that the foreign body was not removed. In such a case, the MRI examination is postponed and the patient is scheduled for screening radiography.

In the event that the removal of the entire metallic foreign body cannot be verified or if there is insufficient information to confirm that there is no metallic foreign body present, screening radiography should be used prior to MRI.

SCREENING ADOLESCENTS FOR METALLIC ORBITAL FOREIGN BODIES

A case report by Elmquist and Shellock (1996) illustrates that special precautions are needed for screening adolescent patients prior to MR procedures. This article described an incident in which a 12-year-old patient accompanied by his parent completed all routine screening procedures prior to MR imaging of the lumbar spine. The patient and parent provided negative answers to all questions regarding prior injuries by metallic objects and the presence of metallic foreign bodies.

While entering the MR system room, the adolescent patient appeared to be anxious about the examination. He was placed in a feet-first, supine position on the MR system table and prepared for the procedure. As the patient was moved slowly toward the opening of a 1.5-Tesla MR system, he complained of a pressure sensation in his left eye. The MRI technologist immediately removed the patient from the MR environment.

Once again, the patient was questioned regarding a previous eye injury. The patient denied sustaining such an injury. Despite that patient’s response, a metallic foreign body in the orbit was suspected. Therefore, plain film radiographs of the orbits were obtained and revealed a metallic foreign body in the left orbit. The patient and parent were counseled regarding the implications of future MR procedures with respect to the possibility of significant eye injury related to movement or dislodgment of the metallic object. This case demonstrates that routine safety protocols may be insufficient for adolescents referred for MR procedures. Accordingly, it is recommended to provide adolescents with additional screening that includes private counseling about the hazards associated with the MR environment.

REFERENCES

Boutin RD, et al. Injuries associated with MR imaging: Survey of safety records and methods used to screen patients for metallic foreign bodies before imaging. Am J Roentgenol 1994;162:189.

Elmquist C, Shellock FG, Stoller D. Screening adolescents for metallic foreign bodies before MR procedures. J Magn Reson Imag 1996;5:784.

Elster AD, et al. Patient screening prior to MR imaging: A practical approach synthesized from protocols at 15 U.S. medical center. Am J Roentgenol 1994;162:195.

Expert Panel on MR Safety, Kanal E, Barkovich AJ, Bell C, et al. ACR guidance document on MR safe practices: 2013. J Magn Reson Imag 2013;37:501-30.

Jarvik JG, Ramsey JG. Radiographic screening for orbital foreign bodies prior to MR imaging: Is it worth it? Am J Neuroradiol 2000;21:245.

Kelly WM, et al. Ferromagnetism of intraocular foreign body causes unilateral blindness after MR study. Am J Neuroradiol 1986;7:243.

Lawrence DA, et al. Undetected intraocular metallic foreign body causing hyphema in a patient undergoing MRI: A rare occurrence demonstrating the limitations of pre-MRI safety screening. Magn Reson Imaging 2015;33:358-61.

Mani RL. In search of an effective screening system for intraocular metallic foreign bodies prior to MR - An important issue of patient safety. Am J Neuroradiol 1988;9:1032.

Murphy KJ, Brunberg JA. Orbital plain film as a prerequisite for MR imaging: Is a known history of injury sufficient screening criteria? Am J Roentgenol 1996;167:1053-5.

Seidenwurm DJ, et al. Cost utility analysis of radiographic screening for an orbital foreign body before MR imaging. AJNR 2000;21:426-233.

Shellock FG. New recommendations for screening patients for suspected orbital foreign bodies. Signals, No. 36, Issue 4, pp. 8-9, 2001.

Shellock FG, Kanal E. SMRI Safety Committee. Policies, guidelines, and recommendations for MR imaging safety and patient management. J Magn Reson Imag 1991;1:97-101.

Williams S, et al. Ferrous intraocular foreign bodies and magnetic resonance imaging. Am J Opthalmol 1998;05:398.

Zhang Y, et al. Tiny ferromagnetic intraocular foreign bodies detected by magnetic resonance imaging: A report of two cases. J Magn Reson Imag 2009;29:704-7.



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