Page 74 - JSOM Winter 2017

Diagnostic Accuracy of Emergency Bedside Ultrasonography
to Detect Cutaneous Wooden Foreign Bodies

Does Size Matter?

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M. Emily Fleming, DO *; Jason Heiner, MD ; Shane Summers, MD ;
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Michael D. April, MD, DPhil, MSc ; Eric Chin, MD 5

ABSTRACT
Background: Soft-tissue occult foreign bodies are a concerning commonly used modality to rule out foreign bodies, they have
cause of morbidity in the emergency department. The identifi- limited utility in the identification of radiolucent substances
cation of wooden foreign bodies is a unique challenge because such as wood. 5
they are often not detectable by plain radiography. The pur-
pose of this study was to determine the diagnostic accuracy Previous studies have examined the use of ultrasound to iden-
of emergency physician–performed ultrasonography to detect tify a variety of materials including wood, metal, plastic, and
wooden foreign bodies of varying sizes. We hypothesized that glass. 6–11 Many of these studies report successful use of ultra-
sonographic sensitivity would improve with increasing for- sound to identify foreign bodies despite limited ultrasound
eign body size. Methods: We conducted a blinded, prospective training. 12–14 Moreover, studies have found that ultrasound
evaluation using a previously validated, chicken, soft-tissue outperforms plain radiography 9,15,16 and computed tomogra-
model to simulate human tissue. We inserted wooden tooth- phy in identifying radiolucent foreign bodies. Beyond these
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picks of varying lengths (1mm, 2.5mm, 5mm, 7.5mm, 10mm) assertions of its superior diagnostic accuracy, ultrasound is an
to a depth of 1cm in five tissue models. Five additional models attractive option for the assessment of retained foreign bodies
were left without a foreign body to serve as controls. Fifty in wounds, given negligible radiation exposure and portability
emergency physicians with prior ultrasonography training for bedside use. 18–20
performed sonographic examinations of all 10 models and
reported on the presence or absence of wooden foreign bod- Reported sensitivity values for the use of ultrasound to detect
ies. Results: Subjects performed 10 ultrasonography examina- foreign bodies vary widely in the existing literature. Published
tions each for a total of 500 examinations. For the detection of sensitivity estimates for the detection of wooden foreign bod-
wooden foreign bodies, overall test characteristics for sonog- ies range from 50% to 100%. The reasons for this vari-
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raphy included sensitivity 48.4% (95% confidence interval ability are unclear. Potential explanations include differences
[CI], 42.1%–54.8%) and specificity 67.6% (95% CI, 61.3%– in operator skill, ultrasound machine variability, inconsistent
73.2%). Sensitivity did not change as object size increased (p = anatomic locations, differing ultrasound settings (e.g., gain,
s.709). Conclusion: Emergency physician bedside ultrasonog- depth, frequency, focal zones), and dissimilar foreign body
raphy demonstrated poor diagnostic accuracy for the detec- characteristics such as size and echogenicity.
tion of wooden foreign bodies. Accuracy did not improve with
increasing object size up to 10mm. Providers should consider The goal of this investigation was to build on the existing lit-
alternative diagnostic modalities if there is persistent clinical erature examining the use of ultrasound to detect wooden for-
concern for a retained, radiolucent, soft-tissue foreign body. eign bodies by examining the association between ultrasound
sensitivity and foreign body size. We hypothesized that sensi-
Keywords: ultrasound; foreign body; wooden object tivity would increase as wooden foreign body size increases.

Methods
Introduction
Study Design and Setting
Detection of cutaneous penetrating foreign bodies can prove We conducted a diagnostic accuracy study of the use of ul-
a difficult task in the emergency department. Failure to trasound to detect wooden foreign bodies of varying sizes in
1
identify and remove these foreign bodies can lead to compli- soft tissue. We conducted the study at San Antonio Military
cations such as infection and result in significant morbidity Medical Center, an academic tertiary care center that largely
and mortality. Historical and physical examination features treats military personnel and beneficiaries in the Greater San
2,3
often have inadequate sensitivity to rule out the existence of Antonio Metropolitan area. The Brooke Army Medical Center
a foreign body. Similarly, although plain radiographs are a Institutional Review Board approved the study.
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*Address correspondence to doc.emfleming@me.com
1 Dr Fleming is at the Department of Emergency Medicine, San Antonio Uniformed Services Health Education Consortium, San Antonio, TX.
2 Dr Heiner is at the Department of Emergency Medicine, San Antonio Uniformed Services Health Education Consortium, San Antonio, TX; the
Division of Emergency Medicine, University of Washington Medical Center, Seattle; and the Department of Emergency Medicine, PeaceHealth
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Peace Island Medical Center, Friday Harbor, WA. Dr Summers is at the Department of Emergency Medicine, San Antonio Uniformed Services
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Health Education Consortium, San Antonio, TX. Dr April is at the Department of Emergency Medicine, San Antonio Uniformed Services Health
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Education Consortium, San Antonio, TX. Dr Chin is at the Department of Emergency Medicine, San Antonio Uniformed Services Health Educa-
tion Consortium, San Antonio, TX.
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