This week’s VOTW is brought to you by Dr. DeStefano and Dr. Wong!
A 3 year old female was brought into the ED a week after a she slid down a wooden pillar and suffered a splinter into her right thigh. A POCUS of the area showed…
Clip 1 is a POCUS of the posterior thigh that shows a small echogenic object with posterior acoustic shadowing. As the they scan through the area, we can tell that the object is linear, about 1cm in length and that its trajectory courses from the dermis to the subcutaneous layer and ends just before entering the muscle. There is no reverbration artifact which is consistent with wood. There is no surrounding signs of abscess of cellulitis.
POCUS for Foreign Bodies
Soft tissue foreign bodies can be imaged by x-ray, CT or ultrasound. Many of us reach for X-rays first but is that really the right move?
X-rays have poor sensitivity for foreign bodies especially for radiolucent objects such as plastic and wood(1).
Ultrasound on the other hand is highly sensitive for foreign bodies, regardless of what the composition, and has the following advantages over X-rays including:
No radiation
Can map out the shape, trajectory, depth of the object at bedside
Evaluate for involvement of tendons, muscles, joints
Evaluate or complications such as cellulitis or abscess
Guide removal of the object in real time (see videos below)
Characteristics of common foreign bodies on US
Glass: hyperechoic, + shadow, + reverb artifact
Metal: hyperechoic, + shadow, + reverb artifact
Wood: hyperechoic, + shadow, - reverb artifact
Plastic: hyperechoic, + shadow, - reverb artifact
Here is an example of metal which is hyperechoic with reverberation artifact (repeated hyperechoic horizontal lines extending deep to the object)
Metal foreign body with reverberation artifact
Technique
Use a linear probe.
Scan the area of interest in both transverse and sagittal.
Look for a hyperechoic structure with posterior shadowing +/- reverbration artifact.
Identify the shape, length, trajectory and surrounding structures.
For very supericial foregin bodies, try using a water bath to increase the distance between the probe and foreign body (this brings the object closer to the "focal point", the part of image with the best "two-point discrimination" or resolution, which is closer to midway down the screen). Water also provides a great acoustic window.
Foreign body removal using ultrasound-guidance
Check out these great videos on how to use ultrasound to assist w/ foregin body removal
Back to the patient:
The team identified the splinter in the soft tissue with no evidence of celluitis or abscess. The team approrpiately did not order an x-ray and saved the patient from unecessary radiation! The patient was referred to outpatient general surgery for evaluation for removal of the object.
References:
Pattamapaspong N et al. Accuracy of radiography, computed tomography and magnetic resonance imaging in diagnosing foreign bodies in the foot. Radiol Med. 2013
https://sjrhem.ca/detection-of-foreign-bodies-in-soft-tissue-a-pocus-guided-approach/