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Background
Foreign bodies (FBs) often challenge diagnosis, as the unaccustomed objects can be incidentally found on imaging studies, or patients may present with complications related to harmful position of a FB that compromises organ activity and function. Children, the incapacitated, retarded or mentally ill patients and alcohol, drug or sexual abusers are among the individuals who are prone to unjustified retention of FBs. In terms of location, FBs can gain access to any system of the body via various routes and mechanisms that can cause serious physical or chemical injury. For example, FBs can enter the orifices of the gastrointestinal (GI) tract through swallowing, ingestion, insertion, iatrogenic misplacement, or because of inherent pathologic conditions. Items can be found in the genitourinary (GU) system following voluntary introduction by the patient, penetrating injury, or after a medical procedure. FBs can enter the respiratory system after aspiration, inhalation, or insertion, and may as well be seen lodged in the ear, throat or nose. Not infrequently, FBs are detected in soft tissue owing to traumatic injury or migration. As much as the variety of FBs is endless, a myriad of complications may ensue associated with impaction, obstruction, perforation, hemorrhage, embolization, chemical dissolution of the material and poisoning, and sepsis. With a clinical presentation triggering amusing and gossipy comments to urgent and life-threatening conditions, the radiologist will assess the imaging findings and set the alarm for intervention. Whether unintentionally or intentionally placed, or incidentally or purposefully discovered, FBs need to be carefully scrutinized because the detection, presumed mechanism of acquisition, and proper management may have medicolegal consequences.

Educational Goals / Teaching Points
We review variability in the imaging presentations of FBs, and illustrate case examples of foreign objects discovered in the GI tract, GU system, respiratory system, and soft tissue.

Key Anatomic/Physiologic Issues and Imaging Findings/Techniques
Radiography plays an important role in the detection of opaque FBs, including metallic objects and pieces of bone or glass. Other, commonly encountered FBs including fish bones, wooden objects and plastic items are not visible on radiographs, and these need to be investigated by fluoroscopy, sonography, or CT.

Conclusion
Radiologists play a key role in the investigation of suspected FBs. Once discovered, FBs need to be characterized in detail, with regard to the anatomic location, type, shape, and chemical composition of the object. Relationships of FBs to adjacent tissues may need to be determined, and serial imaging can be pursued to assess changes in location and orientation until the foreign object is eventually expulsed. Most importantly, on the basis of the imaging findings, radiologists may predict the clinical significance of FBs, ranging from uneventful passage of the object to intended removal by the patient or medical staff, or the occurrence of serious complications including death.