AJR 2001; 176:1155-1159
© American Roentgen Ray Society
Sonography and Radiography of Soft-Tissue Foreign Bodies
L. Kimberlee Horton1,
Jon A. Jacobson1,
Alex Powell2,
David P. Fessell1 and
Curtis W. Hayes1
1
Department of Radiology, University of Michigan Medical Center, 1500 E.
Medical Center Dr., TC-2910G, Ann Arbor, MI 48109-0326.
2
Miami Cardiac and Vascular Institute, Baptist Hospital, 8900 N. Kendall Dr.,
Miami, FL 33176.
Received September 1, 2000;
accepted after revision October 5, 2000.
Address correspondence to J. A. Jacobson.
Introduction
The identification of soft-tissue foreign bodies is not always a
straightforward pursuit. Although routine radiography is the preferred imaging
modality for the initial workup, several types of soft-tissue foreign bodies
are not radiopaque and therefore remain undetected. Because a retained foreign
body may cause infection and inflammation, detection and removal are
imperative [1]. Sonography is
playing an increasing role in the diagnostic process, not only for the
detection of non-opaque foreign bodies but also for the accurate localization
of all types of soft-tissue foreign bodies. Accurate localization can be
valuable in minimizing surgical exploration, or, alternatively, real-time
sonographic visualization can guide percutaneous removal of a soft-tissue
foreign body [2]. Sonography
can also be used to evaluate associated soft-tissue abscess, neurovascular
abnormality, and tendon disorders. This pictorial essay will define the
imaging characteristics of various soft-tissue foreign bodies, comparing their
appearances on sonography and radiography. Familiarity with the imaging
appearances of soft-tissue foreign bodies is critical for an accurate
diagnosis.
Materials and Methods
Foreign bodies of various sizes, shapes, and compositions were placed in
the heel pad of freshly thawed cadaveric specimens. A 5-mm plantar incision
was made with a scalpel and the foreign body was manually inserted through the
incision. The foreign body was placed at a random depth and orientation. The
feet underwent radiography, and then sonography (Model 5200; Acoustic Imaging,
Phoenix, AZ) was performed using a 7-10—MHz linear transducer without a
standoff pad.
General Comments
All soft-tissue foreign bodies are initially hyperechoic on sonography
[1]. However, wooden foreign
bodies may become less echogenic over time
[1]. The conspicuity of
soft-tissue foreign bodies on sonography is increased by a surrounding
hypoechoic halo of granulation tissue, edema, or hemorrhage
[1,
3]. This in vivo response was
not present in the cadaveric specimens used in this study.
Glass does not have to contain lead to be radiopaque—all glass
material is radiopaque to some degree on radiographs
[4]. The higher density and the
effective atomic number of glass compared with the surrounding soft tissue are
the factors responsible for its radiographic appearance
[4]. Common glass products such
as a drinking glass, a light bulb, and the two types of glass used in our
study (the windshield and bottle glasses) contain no lead and yet are
radiopaque [4].
Sonographic artifacts from soft-tissue foreign bodies aid in their
identification. Such artifacts are seen deep in relation to the foreign bodies
on sonography and are not related to the composition of the material; the
surface characteristics of the object influence the type of artifacts
produced, particularly "clean" versus "dirty"
shadowing [5]. Objects with a
small radius of curvature or a rough surface (i.e., a wooden toothpick and
pencil) resulted in clean shadowing
[5]. Objects with a large
radius of curvature or smooth surface (i.e., glass and metal) result in dirty
shadowing and reverberation artifacts
[5,
6].
Windshield Glass
A 5-mm fragment of glass from a domestic automobile was examined
(Fig. 1A). On radiography, the
glass appeared radiopaque (Fig.
1B). On sonography, the glass appeared hyperechoic with posterior
shadowing intermixed with a small amount of reverberation artifact
(Fig. 1C).
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Fig. 1C. —Windshield glass from automobile. Sonogram of plantar surface
of foot reveals hyperechoic glass fragment (solid arrow). Note
posterior acoustic shadowing (open arrows) and reverberation
(arrowhead). C = calcaneus.
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Bottle Glass
A 5-mm piece of glass was obtained from an amber-colored bottle (Anchor
Steam, San Francisco, CA) (Fig.
2A). On radiography, the glass was opaque
(Fig. 2B). On sonography, the
glass was hyperechoic and showed a posterior reverberation artifact and
shadowing from the edges (Fig.
2C).
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Fig. 2C. —Bottle glass. Sonogram of plantar surface of foot reveals
hyperechoic glass fragment (solid arrow). Note posterior
reverberation artifact (arrowhead) and shadowing visible at edges
(open arrows). C = calcaneus.
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Wooden Toothpick
A 5-mm toothpick was selected as an example of a wooden foreign body
(Fig. 3A). On radiography, the
toothpick was not visualized (Fig.
3B), and on sonography it appeared hyperechoic with complete
posterior shadowing (Fig. 3C).
The oblique orientation of the toothpick did not affect the degree of
posterior shadowing. Sonography of a 2.5-mm wooden foreign body shows similar
characteristics (Fig. 3D).
Sonography can reveal wooden foreign bodies as small as 2.5 mm in length with
87% sensitivity and 97% specificity
[1].
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Fig. 3C. —Wooden toothpick. Sonogram of plantar surface of foot reveals
hyperechoic wooden toothpick (in long axis) (solid arrow). Note
complete posterior acoustic shadowing (open arrows). Inset image is
magnification view of foreign body.
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Fig. 3D. —Wooden toothpick. Sonogram of plantar surface of foot after
insertion of 2.5-mm wooden toothpick fragment reveals hyperechoic foreign body
(solid arrow). Note complete posterior acoustic shadowing (open
arrows).
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Pencil Fragment
A fragment from a standard #2 pencil containing wood and graphite was
examined (Fig. 4A). On
radiography, the 4-cm fragment appeared centrally radiopaque, which
represented the graphite, surrounded by the more radiolucent wood
(Fig. 4B). On sonography, the
pencil was hyperechoic and showed complete posterior shadowing
(Fig. 4C).
Sewing Needle
A 15-mm metal sewing needle was examined
(Fig. 5A). On radiography, the
needle appeared opaque (Fig.
5B). On sonography, the small diameter of the needle made it
difficult to identify; however, a bright echo could be seen on close scrutiny
(Fig. 5C). Posterior acoustic
shadowing further aided in localization of the echogenic needle.
Galvanized Steel
A 3 x 7 mm piece of 28-gauge galvanized steel was obtained from a
pipe of a forced-air heating system (Fig.
6A). On radiography, it appeared radiopaque
(Fig. 6B). On sonography, a
bright linear echo was revealed with posterior reverberation artifact caused
by its smooth surface (Fig.
6C).
BB Shot Pellet
A 4-mm zinc-plated steel BB shot pellet
(Fig. 7A) appeared radiopaque
on radiography (Fig. 7B). On
sonography, a bright echo was seen with posterior reverberation artifact
(Fig. 7C).
Stone
A 9-mm common roadside stone was radiopaque on radiography (Figs.
8A and
8B) and showed a bright
irregular echo with posterior acoustic shadowing and minimal reverberation
artifact on sonography (Fig.
8C).
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Fig. 8C. —Stone. Sonogram of plantar surface of foot shows stone as
hyperechoic (solid arrow). Note posterior acoustic shadowing
(open arrows) and minimal reverberation artifact
(arrowhead). C = calcaneus.
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Plastic
A 15 x 6 mm fragment of plastic from an automobile radio was examined
(Fig. 9A). The plastic was not
identifiable on radiography (Fig.
9B). On sonography, the plastic was less echogenic than the other
foreign bodies studied, which may have been a result of its orientation not
being perpendicular to the transducer beam
(Fig. 9C). The plastic foreign
body also showed marked posterior acoustic shadowing, which assisted in
localization of the plastic fragment.
Conclusion
Several soft-tissue foreign bodies, such as wood and plastic, are not
radiopaque and may remain undetected on radiography; however, all foreign
bodies are hyperechoic on sonography. Sonographic artifacts deep in relation
to soft-tissue foreign bodies are related to the surface attributes rather
than the composition of the foreign body and aid in their identification
[1].
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Introduction
Materials and Methods
