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 with suspected orbital foreign bodies prior to MR procedures. Notably, this incident is the only serious eye-related injury that has occurred in the MR environment (i.e., based on a review of the peer-reviewed literature). In consideration of this, the standard policy of performing radiographic screening for orbital foreign bodies in patients or individuals simply because of a history of occupational exposure to metallic fragments needs to be reconsidered.

A study by Seidenwurm et al. evaluated the cost-effectiveness of using a clinical versus radiographic technique to initially screen patients for orbital foreign bodies before MR procedures. The costs of screening were 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. 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. has 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 a patient with suspected metallic orbital foreign bodies involves asking them if they have 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 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 preparation for 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 MRI 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 that adolescents be provided with additional screening that includes private counseling about the hazards associated with the MR environment.

REFERENCES
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