>Detection of Foreign Bodies in Soft Tissue – A PoCUS-Guided Approach

 

Medical Student Clinical Pearl

Sophia Miao, CC4

MD Candidate, Class of 2021

Dalhousie University

 

Reviewed & Edited by Dr David Lewis (@e_med_doc)

All case histories are illustrative and not based on any individual.


 

Case Report

A 33-year-old woman presents to the ED with pain and swelling over the third digit of her right hand.  One week prior to this, she had shattered a jar and a small glass splinter lodged into her finger.  This was promptly removed at home, and the puncture wound healed without intervention.

She presented to the emergency room 7 days later with new pain and swelling surrounding the initial puncture wound.  There is no significant past medical history and most recent Td booster was given 2 years ago.  On examination, there was some mild erythema, swelling, and tenderness on palpation of the lateral aspect of the middle phalanx of the right hand.  She is otherwise well.  You wonder about the possibility of a retained foreign body.


 

PoCUS-Guided Approach to the Detection of Foreign Bodies in Soft Tissue

Foreign bodies in soft tissue are a common complaint in the emergency department, with open wounds comprising 5.7 million (or 4.5% of total) visits to the ED in 2010.[1]  Foreign bodies were found in up to 15% of wounds.[2]  If retained, complications of these include allergic reaction, inflammation, delayed wound healing, damage to adjacent tissue structures, neurovascular damage, tetanus, and infectious complications including cellulitis, necrotizing fasciitis, synovitis, and abscess formation.[3],[4]  Proper detection, and subsequent removal, of retained foreign bodies is therefore essential to evaluate the wound and prevent associated complications.

Diagnosis of a retained FB requires a high index of suspicion.  Clinical suspicion should be raised when there is a compelling history and physical exam.  The latter may include signs of inflammation and/or infection, including warmth, swelling, erythema, tenderness, abscess formation, and discharging wound).[5],[6]

Conventional radiography is known to commonly miss radiolucent materials such as wood and plastic.  It has been shown that plain radiographs have only a 7.4% sensitivity in the detection of wood foreign bodies.5  Remarkably, even glass – a radiopaque material – has been demonstrated to have been missed in up to 35% of x-ray film studies.[7]  There is increasingly compelling evidence for the clinical usefulness and accuracy of bedside ultrasonography in the detection of soft-tissue foreign bodies.  It has been shown to have a specificity of 92% (95% CI = 88%-95%) and sensitivity ranging from 83.3% to 100%.[8],[9]


PoCUS Technique

Probe selection: the use of a high-frequency ultrasound probe is recommended.  This allows for greater axial resolution at the expense of less penetration, which is suitable for the detection of small foreign bodies, as they typically lodge in superficial tissues.[10]

If the wound is open, a transparent covering such as a Tegaderm or probe cover can be used to cover either the wound or probe before scanning.[11]

Medium: standard technique for assessment of soft-tissue structures by ultrasound involves the use of a standoff pad or gel mound.  However, this is not always possible due to the irregular curvature of extremities such as fingers and feet, which may result in poor contact between the probe and skin, decreased field of view, and patient discomfort.  A water-bath technique can circumvent this and has been shown to be superior in such cases.[12]

Method: the area of interest should be scanned in both longitudinal and transverse planes.  Foreign bodies are best detected when the transducer aligns with the longitudinal axis of the foreign body, and therefore revealing the span of the object.[13]  As foreign bodies tend to embed less than 2 cm below the surface of the skin, the depth of field should remain superficial in order to avoid false positives.

US Probe: Ultrasound Water Bath for Distal Extremity Evaluation

 


Findings

Ultrasonography and plain film findings of foreign bodies in soft tissue are summarized in the table below.

Table 1. Ultrasound and x-ray findings of foreign bodies.6,[14],[15],[16]

Material Ultrasound findings X-ray findings
Wood Hyperechoic; may become isoechoic with surrounding tissue as it denatures over time

Posterior acoustic shadowing

Radiolucent, often undetectable
Glass Hyperechoic, bright

Posterior acoustic shadowing

± Posterior comet tail reverberation, diffuse beam scattering

Radiopaque
Plastic Hyperechoic

Posterior acoustic shadowing

Radiolucent, often undetectable
Metal Hyperechoic, bright

Posterior acoustic shadowing

± Posterior comet tail reverberation

Radiopaque

 

Foreign bodies may also display a straight or regular contour.6

 

Image 1 – Wood splinter in volar aspect digit, mildly hyperechoic, surrounding hypoechoic halo, irregular acoustic shadowing

Image 2 – Plastic FB, within tendon sheath, volar aspect digit, brightly hyperechoic, long axis

Image 3 – Plastic FB, within tendon sheath, volar aspect digit, brightly hyperechoic, short axis

 

Image 4 – Glass FB – brightly echogenic, posterior reverberation, FB long axis

 

Image 5 – Metal FB – brightly echogenic, posterior reverberation, FB long axis

 

 

It is important to note that the acoustic shadowing may be complete or partial, as this is dependent on the angle of sonography and foreign body material.[17]  It is also possible to see a hypoechoic halo around the FB, which may be suggest edema, abscess formation, granulation tissue, or other inflammatory process.[18]  As the inflammatory reaction develops, the halo effect becomes more apparent; therefore the foreign body is therefore best visualized by PoCUS several days after the initial injury.6


PoCUS-Guided Foreign Body Removal

There are several options for removal of a foreign body with PoCUS:[19]

  1. Needle localization. Once the foreign body has been identified on PoCUS, a hollow injection needle can be inserted under ultrasound guidance and local anesthetic is delivered through this.  This can be done in either the transverse or longitudinal plane.  The ultrasound probe is then removed, and an incision is made along the needle.  Through the incision site, tweezers or forceps can be used to remove the foreign body.
  2. Real-time ultrasound-guided extraction. This technique is similar to the needle localization method. However, rather than removing the transducer following the needle insertion, the entire procedure is done under direct ultrasound visualization.  The probe is held in the longitudinal plane to visualize both the forceps and the foreign body during the extraction process.

 

There is a risk of obscuring the view of the foreign body on ultrasound with air as a result of the incision itself or through anesthetic delivery.  Saline may be used to irrigate and therefore mitigate the issue.19

The patient’s tetanus status should be verified and updated, if required.  Antibiotic therapy may also be provided, should the risk of infection justify it.


Limitations

There is the possibility of false positives.  Foreign bodies must be differentiated from other hyperechoic body structures, including ossified cartilage, sesamoid bones, scar tissue, gas bubbles, and intermuscular fascia.14  Visualization is therefore important in both longitudinal and transverse planes, as well as comparison with the opposite side.  Acoustic shadowing, hypoechoic halo, and posterior comet tails, if present, can also be indicative of a FB rather than organic body tissue.

Traumatic air injection as a result of penetrating injury can create a scatter artifact on ultrasound, which can be misinterpreted as an acoustic shadow associated with a foreign body.  To differentiate this from a true acoustic shadow, pressure may be applied through the transducer to displace the scatter artifact.6

As is commonplace with all emergency ultrasonography, limitations also include the technical skill of the operator.[20]  A foreign body may also be too small to be detectable by ultrasound.  It is therefore important to remember that a negative scan does not necessarily rule out the possibility of a retained foreign body, and the history and physical examination must be considered in conjunction with the ultrasound findings.

 


 

References

[1] National Center for Health Statistics. Emergency Department Visits. Available from: http://www.cdc.gov/nchs/fastats/emergency-department.htm.

[2] Steele MT, Tran LV, Watson WA, Muelleman RL. Retained glass foreign bodies in wounds: predictive value of wound characteristics, patient perception, and wound exploration. Am J Emerg Med. 1998 Nov;16(7):627-30. DOI: 10.1016/s0735-6757(98)90161-9. PMID: 9827733.

[3] Skinner EJ, Morrison CA. Wound Foreign Body Removal. In:StatPearls. Treasure Island (FL): StatPearls Publishing; 2020. Available from: https://www.ncbi.nlm.nih.gov/books/NBK554447/.

[4] Ebrahimi A, Radmanesh M, Rabiei S, Kavoussi H. Surgical removal of neglected soft tissue foreign bodies by needle-guided technique. Iran J Otorhinolaryngol. 2013 Winter;25(70):29-36. PMID: 24303416; PMCID: PMC3846242.

[5] Levine MR, Gorman SM, Young CF, Courtney DM. Clinical characteristics and management of wound foreign bodies in the ED. Am J Emerg Med. 2008 Oct;26(8):918-22. DOI: 10.1016/j.ajem.2007.11.026. PMID: 18926353.

[6] Atkinson P, Bowra J, Harris T, Jarman B, Lewis D. Point of Care Ultrasound for Emergency Medicine and Resuscitation. Oxford, United Kingdom: Oxford University Press; 2019. DOI: 10.1093/med/9780198777540.001.0001.

[7] Kaiser, C. William MD; Slowick, Timothy MBA; Spurling, Kathleen Pfeifer RN, JD; Friedman, Sissie MA. Retained Foreign Bodies, The Journal of Trauma: Injury, Infection, and Critical Care: July 1997 – Volume 43 – Issue 1 – p 107-111.

[8] Davis J, Czerniski B, Au A, Adhikari S, Farrell I, Fields JM. Diagnostic Accuracy of Ultrasonography in Retained Soft Tissue Foreign Bodies: A Systematic Review and Meta-analysis. Acad Emerg Med. 2015 Jul;22(7):777-87. DOI: 10.1111/acem.12714. Epub 2015 Jun 25. PMID: 26111545.

[9] Atkinson P, Madan R, Kendall R, Fraser J, Lewis D. Detection of soft tissue foreign bodies by nurse practitioner-performed ultrasound. Crit Ultrasound J. 2014 Jan 29;6(1):2. DOI: 10.1186/2036-7902-6-2. PMID: 24476553; PMCID: PMC3922659.

[10] Dean AJ, Gronczewski CA, Costantino TG. Technique for emergency medicine bedside ultrasound identification of a radiolucent foreign body. The Journal of Emergency Medicine. 2003;24(3):303–8. DOI: 10.1016/S0736-4679(02)00765-5.

[11] Chen KC, Lin AC, Chong CF, Wang TL. An overview of point-of-care ultrasound for soft tissue and musculoskeletal applications in the emergency department. J Intensive Care. 2016 Aug 15;4:55. DOI: 10.1186/s40560-016-0173-0. PMID: 27529031; PMCID: PMC4983782.

[12] Krishnamurthy R, Yoo JH, Thapa M, Callahan MJ. Water-bath method for sonographic evaluation of superficial structures of the extremities in children. Pediatr Radiol. 2013 Mar;43 Suppl 1:S41-7. DOI: 10.1007/s00247-012-2592-y. Epub 2013 Mar 12. PMID: 23478918.

[13] Rooks VJ, Shiels WE 3rd, Murakami JW. Soft tissue foreign bodies: A training manual for sonographic diagnosis and guided removal. J Clin Ultrasound. 2020 Jul;48(6):330-336. DOI: 10.1002/jcu.22856. Epub 2020 May 8. PMID: 32385865.

[14] Mohammadi A, Ghasemi-Rad M, Khodabakhsh M. Non-opaque soft tissue foreign body: sonographic findings. BMC Med Imaging. 2011 Apr 10;11:9. DOI: 10.1186/1471-2342-11-9. PMID: 21477360; PMCID: PMC3079678.

[15] Lewis D, Jivraj A, Atkinson P, Jarman R. My patient is injured: identifying foreign bodies with ultrasound. Ultrasound. 2015 Aug;23(3):174-80. DOI: 10.1177/1742271X15579950. Epub 2015 Mar 26. PMID: 27433254; PMCID: PMC4760591.

[16] Campbell EA, Wilbert CD. Foreign Body Imaging. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2020. Available from: https://www.ncbi.nlm.nih.gov/books/NBK470294/.

[17] Anderson MA, Newmeyer WL 3rd, Kilgore ES Jr. Diagnosis and treatment of retained foreign bodies in the hand. Am J Surg. 1982 Jul;144(1):63-7. DOI: 10.1016/0002-9610(82)90603-1. PMID: 7091533.

[18] Little CM, Parker MG, Callowich MC, Sartori JC. The ultrasonic detection of soft tissue foreign bodies. Invest Radiol. 1986 Mar;21(3):275-7. DOI: 10.1097/00004424-198603000-00014. PMID: 3514541.

[19] Paziana K, Fields JM, Rotte M, Au A, Ku B. Soft tissue foreign body removal technique using portable ultrasonography. Wilderness Environ Med. 2012 Dec;23(4):343-8. DOI: 10.1016/j.wem.2012.04.006. Epub 2012 Jul 25. PMID: 22835803.

[20] Pinto A, Pinto F, Faggian A, Rubini G, Caranci F, Macarini L, Genovese EA, Brunese L. Sources of error in emergency ultrasonography. Crit Ultrasound J. 2013 Jul 15;5 Suppl 1(Suppl 1):S1. DOI: 10.1186/2036-7902-5-S1-S1. Epub 2013 Jul 15. PMID: 23902656; PMCID: PMC3711733.

Print Friendly, PDF & Email