The idea that the body naturally expels retained foreign objects is a common misperception. In reality, once a projectile or its fragments lodge within soft tissues or bone, the vast majority remain in place indefinitely, becoming a permanent part of the individual’s anatomy. The body’s primary biological mechanism is isolation, which effectively walls off the inert material. The fate of a retained projectile depends on immediate surgical decisions, the body’s long-term immune response, and the rare possibility of future migration.
Why Projectiles Are Often Left In
Surgeons often decide to leave a bullet or its fragments inside the body when the risk of surgical removal outweighs the risk of retention. This risk-benefit analysis prioritizes the immediate preservation of life and function. A projectile lodged deep within the torso, for instance, may be situated near major neurovascular structures, such as large blood vessels or significant nerve bundles.
Retrieving a bullet from these locations requires extensive dissection that could cause iatrogenic injury, potentially leading to paralysis or uncontrollable hemorrhage. A deeply embedded projectile near major vessels is often safer to leave alone, as surgical exploration could destabilize the patient. Furthermore, high-velocity rounds often shatter upon impact, leaving numerous small fragments that are impossible to retrieve without causing extensive tissue damage.
Initial trauma management focuses on repairing the damage caused by the projectile’s trajectory, not necessarily removing the projectile itself. Once the immediate threat of bleeding or organ damage is addressed, the metallic object is considered inert. If the patient is unstable, or if the bullet is in a region where retrieval would worsen the wound, the surgical team opts for conservative management.
The Body’s Response to Retained Foreign Objects
When a metallic projectile comes to rest in the body, it immediately triggers the foreign body reaction (FBR). This is the immune system’s attempt to neutralize and isolate material it cannot degrade or absorb. The initial phase involves recruiting inflammatory cells, particularly macrophages, to the site.
Since the bullet is too large to engulf, macrophages fuse together to form multinucleated foreign body giant cells (FBGCs). The presence of these cells signals the chronic phase of the reaction, characterized by the recruitment of specialized fibroblasts. These fibroblasts activate into myofibroblasts and begin depositing a dense matrix of collagen fibers around the object.
This collagen deposition leads to the formation of a thick, protective fibrous capsule, effectively walling off the projectile from surrounding viable tissue. The encapsulation stabilizes the projectile, preventing movement and rendering it biologically inert. This scar tissue layer can undergo calcification over time, making the sequestration permanent.
Migration and Spontaneous Ejection
While permanent encapsulation is the standard outcome, the spontaneous movement or ejection of a projectile is an extremely rare phenomenon. Migration typically occurs when the projectile is lodged in a dynamic or fluid-filled environment, rather than being fixed in muscle or bone. One mechanism involves movement within the vascular system, where small fragments can enter a vein or artery and travel with blood flow, potentially leading to arterial embolism.
Movement can also occur in the central nervous system, particularly if a bullet enters the brain’s ventricular system. Here, gravity, the pulsation of cerebrospinal fluid (CSF), and the softening of brain tissue can cause the projectile to slowly sink or move to a new location. Intracranial migration has been reported to occur days to months after the initial injury.
Extremely rarely, a small, superficially lodged fragment may undergo spontaneous cutaneous extrusion, meaning it is slowly pushed out through the skin. This process is driven by chronic inflammation and the body’s persistent attempt to expel material resting close to the surface. However, most movement occurs early after the injury before the fibrous capsule fully forms, and migration is not a typical late-stage outcome.
Chronic Health Risks of Retained Bullets
The long-term presence of a retained projectile, particularly those made of lead or lead alloys, introduces the risk of chronic medical complications. The primary concern is lead toxicity, or plumbism, which arises when lead metal leaches into the bloodstream. This leaching process is accelerated when the projectile is in direct contact with certain body fluids that act as a solvent.
Synovial fluid (which lubricates joints) and cerebrospinal fluid have an acidic pH that promotes the dissolution of lead from the projectile’s surface. When a bullet is lodged in a joint capsule, it can cause lead arthropathy, leading to joint destruction and chronic arthritis alongside systemic lead poisoning. Symptoms of plumbism can be insidious, taking months or years to manifest as fatigue, abdominal pain, or neurological impairment.
The presence of a retained bullet can also cause mechanical interference, even if it is fully encapsulated. A projectile resting within a joint space, for example, can cause chronic pain and severely limit mobility. While most modern projectiles are not strongly magnetic, the presence of metal can interfere with future medical imaging, such as magnetic resonance imaging (MRI), by creating signal artifacts that obscure nearby tissue.