Ultrasound for Retained Radiolucent Foreign Body in Soft Tissue

Author: Stephen Alerhand MD (EM Resident Physician, Icahn School of Medicine at Mount Sinai) (@SAlerhand) // Edited by: Alex Koyfman MD (@EMHighAK)

Situation

A 6 year-old right-handed female patient walks into your ED with her parents complaining of pain to her left hand. According to her parents, the patient began complaining of pain sometime in the afternoon while she was sitting and playing on an old wooden deck with her cousins. Since then, the pain has gotten worse, she has refrained from using the hand, and there is a little bit of redness and swelling to the palmar aspect of the base of the left hand. The parents suspect that there is a wooden splinter in the patient’s hand.

girl with splinter

On examination, the patient is reluctant to close her fist. You cannot externally visualize any splinter or foreign body (FB), although your photographic memory reminds you that 38% of retained FB in soft tissues are overlooked on initial exam [1]. The patient allows you to palpate the involved skin, although it is tender to touch. Pulses, capillary refill, and sensation are intact.

Your immediate thought is to agree with the parents, that there may be a foreign body retained in the soft tissue of the hand. The hand does not look infected at this time, but you know that the most common complication of a retained FB – soft tissue infection – may develop over time. Nerve injury, though less likely, may also occur.

You start with an x-ray of the hand, but no foreign body is visualized. Of course, your photographic memory again reminds you that only 15% or less of wooden FB are detected with radiography [1]. For reference, x-rays have been shown to detect radiopaque foreign bodies such as glass 85% of the time [2], but given the clinical history, a wooden foreign body is much more likely.

So now what?

Is it worth blindly dissecting through the skin at the bedside to locate and remove the foreign body? Should you call the Plastic Surgery team for a possible operation? Should you treat with antibiotics? Should you leave the hand (and possible foreign body) alone?

Relevant Literature

Mizel MS, Steinmetz ND, Trepman E. Detection of wooden foreign bodies in muscle tissue: experimental comparison of computed tomography, magnetic resonance imaging, and ultrasonography.
Objective: To compare CT, MRI, and US for detection of wooden FB in muscle tissue
Type of Study: Experimental
Results: Largest wooden FB (min 10 mm width) easily detected by all 3 modalities. FB of all sizes soaked in cadaver for 5 months best detected by MRI. Smallest splinters (min 1-4 mm) placed distant from bone detected most easily by US; those soaked for 5 months in cadaver best detected by US or MRI; those soaked 3 days and placed near bone not reliably detected by any method.
Conclusion: Either US or MRI may be best initial imaging modality for suspected wooden FB; depends on symptom chronicity, proximity to bone, and availability of imaging modality.

Jacobson JA, Powell A, Craig JG, Bouffard JA, van Holsbeeck MT. Wooden foreign bodies in soft tissue: detection at US. Radiology. 1998 Jan;206(1):45-8.
Objective: To evaluate US use for detection of wooden FB implanted in cadavers.
Methods: Wooden FB randomly placed in plantar soft tissues of three cadaver feet. 10 FB were 2.5 x 1.0 mm. 10 FB were 5.0 x 1.0 mm. 10 incisions made without FB. Three MSK radiologists performed blinded US.
Results: For 2.5 mm long FB, sensitivity and specificity were 86.7% and 96.7%, respectively. For 5.0 mm long FB, sensitivity and specificity were 93.3% and 96.7%, respectively.
Conclusion: US can be used to effectively locate wooden FB as small as 2.5 mm in length. Since many FBs are radiographically undetectable, accuracy and availability of US make it an excellent modality for evaluating for radiolucent FB.

Gilbert FJ, Campbell RS, Bayliss AP. The role of ultrasound in the detection of non-radiopaque foreign bodies. Clin Radiol. 1990 Feb;41(2):109-12.
Objective: To assess value of US for detecting non-radiopaque FB in extremities.
Results: US detected 21/22 FB. 3 false-positives. Sensitivity 95.4%, specificity 89.2%, PPV 87.5%, NPV 96.2%.
Conclusion: US is a reliable method for detecting non-radiopaque FBs, making significant contribution to patient management.

Crawford R, Mathewson AB. Clinical value of ultrasonography in the detection and removal of radiolucent foreign bodies. Injury. 1989 Nov;20(6):341-3.
Objective: To evaluate the use of US for diagnosing FB in the hand
Methods: 39 patients with suspected retained FB in hand in whom plain films were negative were assessed by US.
Results: US localized 19/20 radiolucent FB. 2 false-positives.
Conclusion: US is sensitive and accurate for diagnosing FBs otherwise difficult to find by conventional radiographic techniques. Provides accurate 3D localization, which is valuable to surgeon at operation.

Hill R, Conron R, Greissinger P, Heller M. Ultrasound for the detection of foreign bodies in human tissue. Ann Emerg Med. 1997 Mar;29(3):353-6.
Objective: To determine the accuracy of detection of wood and plastic FB in human tissue by relatively experienced clinicians.
Methods: Blinder scanner searched for FB in tissue in which uniform wood and plastic FB were placed.
Results: N=80 punctures. US detected 44 of 53 FB (83% sensitivity). Wood FB detected 25/27 (93%) and plastic FB detected 19/26 (73%) (p=13). 11 False-positive readings (59% specificity).
Conclusion: US imperfect but may be useful in screening for superficial FB in human tissue.

Bray PW, Mahoney JL, Campbell JP. Sensitivity and specificity of ultrasound in the diagnosis of foreign bodies in the hand. J Hand Surg AM. 1995 Jul;20(4):661-6.
Objective: To determine sensitivity/specificity of US in diagnosis of FB in hand.
Methods: 15 cadaver hands. Two sizes of three different materials (wood, glass, metal). FB assigned to 50% of hands. Scans by blinded radiologist.
Results: Of 166 FB inserted, 156 detected by US. 10 false-negatives (sensitivity 94%). 1 false-positive and 148 true negatives (specificity 99%).
Conclusion: High specificity of US allows FB presence to be confirmed given a positive result. A combo of US and x-ray should allow diagnosis and localization of virtually all FBs in hand.

Blyme PJ, Lind T, Schantz K, Lavard P. Ultrasonographic detection of foreign bodies in soft tissue. A human cadaver study. Arch Orthop Trauma Surg. 1990;110(1):24-5.
Objective: To assess usefulness of US in detecting FB.
Methods: Blind study in human cadavers using glass, plastic, and wood FB.
Results: Of 65 FB in 102 cadavers, 58 were found. Sensitivity 89%, specificity 93%.
Conclusion: US is a useful clinical tool for detecting soft tissue FBs.

Manthey DE, Storrow AB, Milbourn JM, Wagner BJ. Ultrasound versus radiography in the detection of soft-tissue foreign bodies. Ann Emerg Med. 1996 Jul;28(1):7-9.
Objective: To determine the usefulness of US and x-rays in detecting FB in soft-tissue models.
Type of Study: Randomized, blinded descriptive study. 120 chicken thighs evaluated for FB by two radiologists using 2-view radiography and linear US transducer. FB of all types inserted into 60 thighs.
Results: US sensitivities: gravel 40%, metal 45%, glass 50%, cactus spine 30%, wood 50%, plastic 40%. Overall US sensitivity 43%, specificity 70%, false-negative 50%, false-positive 30%. X-rays detected radiopaque FB (gravel, glass, metal) 98% of time, but never radiolucent FB (wood, plastic, cactus spine). False-negative 50%, false-positive 1.6%.
Conclusion: US detection of FBs by skilled operators showed poor sensitivity and specificity. US should not be relied on to rule out retained FB in distal extremities. Radiography highly sensitive for FBs that are radiopaque only.

How to Perform Ultrasound of Soft Tissue to Visualize A Retained Foreign Body
  • Use linear transducer (7.5 to 10 MHz) to scan in both longitudinal and transverse orientations.
  • Water bath can enhance visualization.
    • water bath
    • Screen Shot 2016-06-20 at 3.22.23 PM
    • (portrayal of visual enhacement)
    • http://emedicine.medscape.com/article/826498-workup
  • The FB appears hyperechoic with surrounding hypoechoic rim (inflammatory reaction if retained for > 24 hours).
  • Wood or plastic FB usually produce posterior shadowing.
    • Screen Shot 2016-06-20 at 3.10.18 PMhttps://www.acep.org/content.aspx?id=83271
    • Metal FB usually produces reverberation or comet tail artifact.
      • Screen Shot 2016-06-20 at 3.19.00 PMhttp://www.sonoguide.com/foreign_bodies.html
  • Visualization is more difficult if FB is adjacent to bone or deep to subcutaneous tissue
  • False positives: calcification, scar tissue, fresh hematoma, air trapped in soft tissues. However, these can often be correlated clinically.
  • Measure the depth of FB from skin surface.
  • Mark the skin for FB removal if indicated, while noting surrounding vessels and nerves.

 

Further References

  1. Anderson MA, Newmeyer WL, Kilgore ES. Diagnosis and treatment of retained foreign bodies in the hand. Am J Surg 1982;144:63-67.
  2. Cambridge textbook of accident and emergency medicine. Cambridge University Press. ISBN:0521433797.
  3. http://radiopaedia.org/articles/glass-foreign-bodies
  4. http://pubs.rsna.org/doi/pdf/10.1148/radiographics.21.5.g01se271251
  5. www.sonoguide.com/foreign_bodies.html

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