The most frequent sites of localization of foreign bodies are: rectum,
vagina,
upper airways (i.e.
in case of aspiration),
digestive tract (ingestion) or the soft tissues.
Visualization of a foreign body in different imaging modality depends on the position,
composition and size of the object itself.
Correct identification of a possible foreign body and its location plays a crucial role since they can be burdened by complications such as infection,
inflammation and severe pain.
Although the vast majority of objects ingested or inserted through a body cavity pass through the gastrointestinal tract without significant problems,
causing only minor mucosal injury [2],
it is not uncommon that they can be responsible for intestinal obstruction or perforation,
hemorrhage,
abscess formation or even septicemia.
Perforation due to the presence of a foreign body may occur in any tract,
(i.e.
ileum,
ileocecal and rectosigmoid tracts) [3].
Other conditions that may result in the placement of a foreign body are motor vehicle accidents and gunshot wounds.
Visualization of a foreign body with different imaging modalities depends on the location,
as well as on the physical characteristics and density of the object itself.
Metallic objects,
with the exception of aluminum,
are radiopaque,
as well as foreign bodies made of most animal bones and all the glass ones,
while most of plastic and wooden foreign bodies (i.e.
cactus spines,
splinters) and fish bones are not radiopaque.
Therefore,
their visualization may be quite challenging.
In general,
we can assume that a foreign body can be seen when the contrast between it and surrounding tissues is adequate; so,
it is not rare that a foreign body could be not visualized with a technique and successfully detected with another.
Diagnosis of non-radiopaque objects can be more difficult.
In selected cases,
CT and ultrasound can visualize suspected non-radiopaque foreign bodies,
such as wood,
acrylic and bakelite.
Radiography
Plain radiography of thorax or abdomen represents the first exam in the suspect of a foreign body.
Conventional classical radiographs may allow visualization of radiopaque objects standing out from the surrounding tissues and,
although with limited spatial resolution,
they may help the radiologist to determinate whether the object is in a critical position.
Therefore,
for a better localization and definition of the foreign body,
further imaging modalities may be necessary.
Ultrasonography
Advantages in the use of ultrasound for the evaluation of foreign bodies are well-described: no exposure to ionizing radiation,
real time images and relatively inexpensive technique.
Ultrasounds have shown promising results,
particularly in the detection of radiolucent foreign bodies,
with a sensitivity of up to 95% [4].
If a foreign body is located superficially,
can be visualize and locate optimally with US,
more efficiently than CT or radiographic examination.
On US examination of superficial tissues,
foreign bodies are usually hyperechoic.
US is a very sensitive exam for localization of superficial foreign bodies,
as well as for guiding their removal.
However,
it loses its effectiveness in visualization of foreign bodies located deep inside or inside the air-filled cavities.
CT
CT can represent a diagnostic completion survey after conventional radiography.
It can be used successfully in the definition of the location,
shape and size of the foreign body.
Some authors suggest its use as a first-instance examination for the visualization of foreign bodies.
Even if a high dose of radiation is given to the patient,
CT is able to provide comprehensive information about the intrinsic characteristics of the foreign body thanks to its high spatial resolution,
allowing,
in some cases,
even the correct identification,
the location and the presence of any complications (i.e.
perforation,
occlusion,
hemorrhage).
On the other hand,
CT has some limitations in the visualization of some foreign bodies,
particularly for plastic objects that may not be highlighted,
while radiopaque foreign bodies such as bones may not be effectively visualized [5].
Sometimes they also may be misinterpreted as focal soft tissue lesion due to their unusual appearance and location.
MRI
Most foreign bodies are not clearly visualized on MRI exam,
but they can be responsible of sever artifacts.
In addition,
all patients must undergo extensive screening for foreign bodies before undergoing an MRI study [3].
The presence of ferromagnetic foreign body is one of the major contraindication for MR exam due to the potential damage.