Identification and topographic localization of metallic foreign bodies by metal detector

https://doi.org/10.1016/j.jpedsurg.2004.04.011Get rights and content

Abstract

Objective

Exact localization of ingested metal objects is necessary to guide therapy. This study prospectively evaluates the accuracy of foreign body (FB) identification and localization by metal detector (MTD) in a systematic topographic fashion.

Methods

Patients who presented after an alleged or witnessed metal FB ingestion were scanned with an MTD. In case of a positive signal, the location was recorded in a topographic diagram, and radiographs were obtained. The diagnostic accuracy of the MTD scan for FB identification and topographic localization was determined by χ2 analysis, and concordance was calculated by the McNemar test and expressed as κ.

Results

A total of 70 MTD examinations were performed on 65 patients (age 6 months to 16 years); 5 patients were scanned twice on different days. The majority had swallowed coins and button batteries (n = 41). Of these, 29 items were correctly identified, and 11 of 12 were correctly ruled out (coins and button batteries: sensitivity, 100% [95% Confidence Interval 95% to 100%]; specificity, 91.7% [95% CI 76% to 100%], κ = 0.94). When all metallic objects were included, 41 of 46 were correctly identified, and 22 of 24 were correctly ruled out (sensitivity, 89.1% [95% CI 80% to 98%]; specificity, 91.7% [95% CI 81% to 100%], κ = 0.78). Five miscellaneous objects were not identified (sensitivity for items other than coins and button batteries 71% [95% CI 49% to 92%], κ = 0.56). Localization by MTD was correct in 30 of 41 identified objects (73%). The error rates of junior and senior pediatric surgery residents did not differ significantly (P = .82).

Conclusions

Ingested coins and button batteries can be safely and accurately found by metal detector. For these indications, the MTD is a radiation-free diagnostic alternative to conventional radiographs. Other items, however, cannot be ruled out reliably by MTD. In these cases, radiographic imaging is still indicated.

Section snippets

Materials and methods

Patients who presented to our emergency department after an alleged or witnessed ingestion of a metal foreign object were prospectively and consecutively enrolled. Exclusion criteria were respiratory compromise, presence of metallic hardware, or previous diagnostic imaging for the current FB ingestion. Informed consent was obtained from the accompanying parent or guardian for participation in the study. Figure 1 schematically demonstrates the principles of how an MTD works.

The pediatric

Results

A total of 70 MTD examinations were performed on 65 patients (age 6 months to 16 years, mean 4.1 years) over a period of 20 months; 5 patients were scanned twice on different days of presentation by different individuals. One patient’s family refused to participate in the study because of “lack of time.” The majority of objects reported by the caregiver to have been potentially or actually swallowed were coins and button batteries followed by other items including jewelry, tools, needles, and

Discussion

Lewis7 described the first clinical application of metal detection to identify a swallowed coin in 1980. Since then, MTDs have been used by otolaryngologists,8 radiologists before MRI studies9 and forensic experts and trauma surgeons to look for bullets and missile shrapnel.10, 11, 12

Several controlled studies using an MTD to identify swallowed metal objects have been performed in the pediatric population, with reported sensitivities exceeding 96% and specificities above 81%.2, 3, 6, 13, 14

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