by Tim B. Hunter, MD and Mihra S. Taljanovic, MD, PhD
Foreign Body Injuries
Even the most sheltered individual has a life filled with a multitude of minor injuries, including falls, cuts, abrasions, scratches, and burns. Everyone has suffered puncture wounds from splinters, needles, and thorns and has been cut with glass. The entire range of possible foreign body injuries cannot be covered herein. However, it is possible to illustrate many common types of accidents and point out general principles concerning these injuries (Table).
Jewelry, clothing, and items lying on a patient, or in a patient's clothing may simulate a foreign body (figures: materials simulating foreign bodies). When viewing or interpreting imaging studies, one should always take care to identify all objects seemingly in or on a patient, including medical devices, foreign bodies, and generally innocuous items which simulate a medical device or foreign body.
Foreign Body Injuries: general principles
Category
Description
General Principles
Diagnosis may be difficult and require CT, US, or other techniques to identify nonopaque foreign bodies
Predisposed Patients
Children and mentally incompetent adults
individuals with a history of recent trauma who cannot furnish a history
individuals who undergo instrumentation, surgery, or non-conventional medical treatments
individuals who have "unusual" sexual practices, engage in wizardry or sorcery, abuse drugs or alcohol, or engage in criminal activities
victims of physical abuse or terrorist attack; military personnel; individual with hazardous occupations - police and fire protection, heavy industry, construction, mining
Complications
Pain, swelling, tenderness, cellulitis, abscess formation, sepsis, migration of foreign object to distant locations with potential vascular or nerve injury
Bullets
Bullet wounds are far too common in the United States (figures: foreign body injuries I). A detailed review of these injuries is beyond the scope of this discussion except for a few general comments from more extensive reviews on the subject (Wilson, 1999; Hollerman, 1994; Dodd, 1990). Handguns usually fire relatively "low-velocity" single bullets with speeds less than 2000 ft/sec (610 m/sec). Rifles typically fire high-velocity solitary bullets with speeds above 2000 ft/sec (610 m/sec). Shotguns usually fire multiple metallic pellets (BBs, buckshot, or birdshot). The most common shotguns are 12 and 20 gauge. Gauge describes the number of lead balls fitting the shotgun barrel that total one pound (0.45 kg) in weight in a 0.410 inch bore (internal diameter) barrel (Dodd, 1990).
Bullets are often described by their caliber, which is a measurement of their diameter in inches or in millimeters or the internal diameter (bore) of the gun barrel holding the bullet, such as 22 (5.6), 32 (8.1), 38 (9.7), and 45 (11.4) calibers representing, respectively, the hundredths of an inch or (mm) of the bore (Dodd, 1990). Although the caliber of a bullet is important, it has only a loose relationship to the weight of the bullet and the size of its charge. Its velocity is also a very important parameter, as its kinetic energy varies by the square of the bullet velocity. Kinetic energy relates directly to how much tissue damage a bullet causes.
Bullets are most commonly composed of lead. They may be fully or partially covered by an outer metal jacket (full metal jacket) that is usually composed of copper. If a bullet has a hollow cavity at its tip (hollow-point bullet), it will deform more on impact and produce more tissue damage. When it comes to rest, a hollow-point bullet typically has a mushroom shape. Bullets are not sterile, and gunshot wounds can deposit live bacteria and other contaminants deep into the body.
Shotgun pellets are measured by their gauge: the larger the number, the smaller the pellet size. Because the pellets are round, they do not travel through air or tissue as well as the more aerodynamically shaped bullets. However, the combined mass of multiple pellets striking someone at a small distance from the gun barrel can cause severe soft-tissue and bone damage - a relatively large mass is decelerated over a short distance, and its kinetic energy is deposited in a small volume of tissue (figure: accidental shotgun injury).
Shotgun pellets used for hunting were formerly composed of lead. Nowadays, they often have a composition of steel, bismuth, and tungsten. Lead is not ferromagnetic. However, lead pellets left in the environment produce considerable toxic effects on waterfowl. Because steel composite pellets may be ferromagnetic, they may undergo dangerous motion if a patient with embedded steel shotgun pellets is exposed to a strong magnetic field; therefore, MR imaging may be contraindicated in such patients (Eshed, 2010).
It is sometimes possible to distinguish steel and lead pellets from one another at radiography (Wilson, 1999). Lead pellets tend to be deformed and fragmented by impact with soft tissues and bone. Steel pellets usually remains round. Unjacketed bullets are composed of lead and should not cause any problems for MR imaging. On the other hand, some bullet jackets are composed of steel rather than copper. If the nature of the bullet injury is unknown, it may not be safe to perform MR imaging on a bullet wound victim if radiographic findings suggest that the embedded bullets are jacketed (Eshed, 2010; MRI Safety Information; MRIMaster.com; RadiologyInfo.org). The major problem in deciding whether to use MRI for a paitent with a gunshot wound is accurate identification of the bullet composition. Usually the bullet itself or its jacket are not available (Fountain, 2020).
Future sophisticated dual energy CT routines look promising for diffentiation between steel containing and non-steel containing jackets of bullets composed of lead for the triage of gunshot victims for MRI examination (Gascho, 2019). Also, work by Fountain (2020) suggests bullets that fragment on entry with a narrow metallic debris trail on radiography or CT and limited penetration are composed of nonferromagnetic material and pose little risk for MRI. On the other hand, nondeformed bullets without a debris trail could be solid or jacketed and could be composed of steel, nickel, or copper. In this situation, it is best to consider these bullets to be ferromagnetic until proven otherwise (Fountain, 2020).
BB guns are air powered guns which shoot metallic ball projectiles (BBs), which vary in size but are often 4.3-4.4 mm in diameter. The balls are composed of steel and are zinc or copper plated to resist corrosion. They have low penetrating power and usually do not deform. They are generally found in subcutaneous tissue or muscle. BBs have no significant torque at MRI and are safe for most imaging applications, though their steel composition does produce MRI distortion (Fountain, 2020).
Most lead bullet fragments can be left in place. They usually become encapsulated with fibrous tissue (figure: bullet in breast). Lead toxicity is a potential problem if the lead fragments are in a joint space, bursal space, or disc space (figure: lead fragments in joint) (Marquez, 2018). Lead fragments left in a joint space also can lead to a severe, destructive synovitis (Hollerman, 1994).
Materials Simulating Foreign Bodies or Medical Apparatus
Underwear simulating pelvic foreign body
"Buckshot bra"
Decorative design on underwear simulates a vaginal or bladder foreign body
A woman's bra is packed with metallic shot to make her breasts appear larger. (Courtesy Ken Sandock, MD)
e-cigarette
Earrings: lateral view
Earrings: AP view
64 year-old woman who had postoperative bowel obstruction. A supine view of the abdomen shows an e-cigarette the patient had hidden in her hospital gown.
These earrings resemble cervical spine apparatus on the lateral view.
Foreign Body Injuries: I
Bullet in foot
Shrapnel in hand
Bullet debris
Young man shot in the foot with a handgun. There is a fifth metatarsal fracture and deformed bullet fragment. The BB overlying the cuboid is from a remote injury.
Young man with multiple pieces of shrapnel in the hand after gunshot injury.
Young man shot in the knee with multiple bullet debris in the soft tissues about the knee as well as in the knee joint.
Shotgun injury
Bullet in liver on ultrasound
Bullet in breast
Young man who accidentally shot himself in the chest and right arm with a shogun. The scout view from a chest CT shows multiple pellets in the right shoulder and right chest wall with contusion of the right upper lobe. A right chest tube, an endotracheal tube, and a nasogastric tube are in place. A CT image of the lower portion of the chest shows an inferior pellet in the right ventricle. It had penetrated the right subclavian vein and embolized to the right ventricle. It was visible bouncing in the right ventricle when fluoroscopy was performed during right upper extremity angiography. The pellet was successfully removed at cardiac catheterization. (Courtesy Michael Rosellini, MD)
Transverse ultrasound image of an elderly man with a bullet (arrow) in his liver. He had a history of a gunshot wound many years previously, and the bullet was an incidental finding. From Hunter, 2003. Permission granted for use of images in this article by Radiological Society of North America (RSNA)
A bullet in the left breast from an old injury was incidentally noted on mammography. From Hunter, 1994
