Metal Detectors and Foreign Bodies: Parlor Trick or Diagnostic Tool?
Source: Younger RM, et al. Handheld metal detector confirmation of radiopaque foreign bodies in the esophagus. Arch Otolaryngol Head Neck Surg 2001;127:1371-1374.
The authors undertook a prospective study of patients to answer a simple question: Can a handheld metal detector be used to assess the progress of an ingested metal object through the gastrointestinal (GI) tract? The authors studied 139 consecutive children presenting to a tertiary pediatric referral center after metallic foreign body ingestion. The initial diagnosis was obtained with a plain radiograph. When it was determined that the foreign body was lodged in the esophagus and would require endoscopic removal, the handheld metal detector (Garrett Super Scanner, Garret Security Systems, Garland, Texas) was passed in a slow, zig-zag fashion across the ventral and dorsal aspects of the chest and abdomen. The suspected location was marked on the skin. All patients underwent both radiographic evaluation and handheld metal detector scanning of the chest and abdomen on presentation and immediately before endoscopic removal. The locations as determined by all these methods were compared.
Twenty-six of 139 children met eligibility criteria and completed the study protocol. The authors required a delay of at least six hours from the time of diagnosis to the time of endoscopic removal for inclusion in the study. This was to permit adequate time for spontaneous passage past the gastroesophageal (GE) junction. The handheld scanner correctly identified the location of the object in all 26 patients. All foreign bodies were coins; 24 were lodged at the sternal notch, one was below the sternum, and one was at the GE junction. In addition, one patient was excluded because no radiograph had been obtained prior to endoscopy, but handheld scanning correctly identified that the coin had passed into the stomach. The authors conclude that handheld metal detectors accurately can assess the progress of coins through the esophagus prior to endoscopy without additional radiographs. Initial radiographs still are indicated for appropriate diagnosis of the type and location of the foreign body.
Commentary by Richard J. Hamilton, MD, FAAEM, ABMT
The initial radiographic study of foreign body ingestions yields valuable information including size, shape, orientation, location, and type (coin, battery, toy, etc.) of foreign body, as well as mediastinal or thoracic complications from resultant esophageal perforations. However, many esophageal foreign bodies pass uneventfully through the gastrointestinal tract, and having to reassess patients with repeat radiographs to determine the progress of the object introduces additional radiation exposure and delays in disposition. A technique such as this would be extremely useful in assessing progress of the coin at frequent intervals and avoiding endoscopy if the coin has passed into the stomach.
Handheld metal detectors offer other, distinct advantages in the assessment of the metallic foreign body in the GI tract. Case reports describe successful identification of thin or aluminum foreign bodies that radiographs have missed—such as thin razor blades, pins, or aluminum pop-top tabs. Sensitivity and specificity are 90-100%, and the negative predictive value has been at or near 100% in a number of studies. No study has assessed the value of using the metal detector as an initial tool in determining location of metallic foreign body, but many of my colleagues claim success in differentiating between foreign bodies lodged in the esophagus vs. in the stomach or intestine. A formal study of this technique in patients who have asymptomatic coin ingestions would be interesting.
I had viewed this particular technique with some suspicion, as I was not confident that the location by metal detector would be anatomically accurate. This study has changed my mind to some extent. I think that once a radiograph has been obtained to identify the location and type of object ingested, this technique can be used to assess progress of that object, avert delayed radiographs, and allow for more rapid discharge from the ED.
Dr. Hamilton, Associate Professor of Emergency Medicine, Program Director, Emergency Medicine, MCP, Hahnemann University, Philadelphia, PA, is on the Editorial Board of Emergency Medicine Alert.
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